AN ECOSYSTEM VIEW OF MANAGEMEN RESEARCH

IN

THE MYAKKA RIVER

- , Review of Phase I and Phase 11 Reports

Review of Draft Report on Evaluation of Water Quality Impacts

Review of Ecosystem Models on Estuarine Management Problems

Proposed Work

Joan A. Browder Miami Laboratory

Southeast Fisheries Center National Marine Fisheries Service

Miami, Florida

July, 1987

In t roduc t ion " .

The p r i n c i p a l purpose of t h e Phase I and Phase I1 s t u d i e s was to gain

information f o r eva lua t ing t h e p o t e n t i a l impacts on r i v e r ecosystems and

resources o f decreased runoff to the Myakka River. Despi te t h i s emphasis,

cons iderable information was c o l l e c t e d t h a t a l s o w i l l be u s e f u l in eva-

l u a t i n g t h e p o t e n t i a l impacts of i nc reas ing t h e n u t r i e n t load of the Myakka

River , which i s another major management concern. The r e p o r t s support t h e

development of a conceptual framework with which t o eva lua te the response

o f t h e n a t u r a l resources of the r i v e r to land use and water manage-

ment changes of a l l types; t hey c o n t r i b u t e to an understanding of the r i v e r

a s an ecosystem. Developing such an understanding should be the f i r s t

s t e p in eva lua t ing impacts. The Phase I and Phase I1 r e p o r t s suggested

that s a l i n i t y has a major in f luence on the d i s t r i b u t i o n of benth ic orga-

nisms and f i s h in the r iver - the i r occurrence and dens i ty . Fu tu re inves t i -

g a t i v e w r k i n the r i v e r w i l l b e n e f i t from the emphasis on the s p a t i a l

d i s t r i b u t i o n of p l a n t s , animals , and s a l i n i t y t h a t was given in the Phase

I and Phase I1 repor t s .

C lea r ly , s a l i n i t y is an important v a r i a b l e a f f e c t i n g p l an t and animal

d i s t r i b u t i o n s ; t h i s mst be recognized in any a n a l y s i s of the p o t e n t i a l

e f f e c t on the r i v e r of water management o r land use changes. S a l i n i t y

e f f e c t s on b i o l o g i c a l organisms w i l l have to be taken i n t o account in exa-

mination of the e f f e c t of changes in n u t r i e n t load. The s a l i n i t y p r o f i l e

o f t h e r i v e r w i l l he lp desc r ibe how n u t r i e n t concent ra t ions change a s r i v e r

water mixes wi th Char lo t t e Harbor water. Phys ica l condi t ions in the- r i v e r

such as tu rbulence , bottom scouring, and c i r c u l a t i o n and the mixing of

1

water masses, undoubtedly change s i m i l a r l y t o changes in s a l i n i t y ; corre la-

t i o n of these condi t ions with s a l i n i t y w i l l help us to descr ibe t h e i r . * . v a r i a t i o n in the r i v e r over t i m e and t o evalua te poss ib le impacts of these

changes on r i v e r organisms.

Nutr ients such a s n i t rogen a r e d r iv ing fo rces in primary production

and the t r a n s f e r of energy through aqua t i c food webs. Concentrat ions of

n u t r i e n t s may vary both a s a funct ion of r i v e r flow and independently of

it. These r e l a t i o n s h i p s , a s wel l a s s a l i n i t y e f f e c t s , need to be addressed

i n eva lua t ing p o t e n t i a l impacts of a l t e r i n g freshwater inflow t o the system.

My review of the Phase I and Phase I1 r e p o r t s has been from the point

o f view of t r y i n g to learn the mst important a spec t s of the s t r u c t u r e of

t h e system in terms of forc ing funct ions , components ( o r compartments), and

major energy flows. For t h i s reason, I have been i n t e r e s t e d in determining

(1) dominant primary producers-types and species ; (2 ) dominant species of

f i s h and t h e i r genera l food hab i t s ; ( 3 ) dens i ty and biomass dens i ty of f i s h

and inve r t eb ra te spec ies and t h e i r v a r i a t i o n over time and space; (4) major

r i v e r zones and h a b i t a t s ; and (5) s p a t i a l and temporal va r i a t ion in major

environmental va r i ab les such a s s a l i n i t y and n u t r i e n t concentrat ions. Of

major importance is the determination of how s a l i n i t y and n u t r i e n t con-

c e n t r a t i o n s vary in r e l a t i o n s h i p t o r i v e r flow a d , then , how t h e o v e r a l l

abundance and biomass of n a t u r a l resources i s a f f e c t e d by s a l i n i t y and

n u t r i e n t concentrat ions. Another t o p i c of i n t e r e s t is how physica l con-

d i t i o n s in t h e r i v e r , such a s scouring, turbulence , etc., vary with r i v e r

f low and how p l a n t s and animals of the r i v e r respond t o v a r i a t i o n in physi-

c a l condftions. Information on mst of these s u b j e c t s was contained in the

r e p o r t s a t various l e v e l s of d e t a i l .

I ob ta ined a genera l idea of food h a b i t s of dominant f i s h spec ie s of

t h e r i v e r by a cursory l i t e r a t u r e review. Lacking biomass da ta , which was

beyond the scope of the Phase ; and Phase I1 s t u d i e s , I used q u a l i t a t i v e

information on vegeta t ion w v e r a g e and dens i ty e s t i m a t e s on f i s h and

-benthic i n v e r t e b r a t e s to approach these topics . . Futu re work t h a t I propose i s based on the ecosystem pe r spec t ive I

have gained from the Phase I and Phase I1 r e p o r t s w d my a n c e l l a r y inves t i -

g a t i v e e f f o r t s . The work inc ludes w d e l i n g . Although t h e study could be

conducted without models, m d e l i n g can i n t e g r a t e a l l t h e elements of the

s tudy and make r e s u l t s w r e meaningful. Quantifying a prel iminary w d e l is

t h e b e s t way I know to estimate in advance whether suspected e f f e c t s a r e of

s u f f i c i e n t magnitude to be important. Seen from the pe r spec t ive t h a t pre-

l iminary modeling might provide us, some elements of t h e s tudy t h a t I pro-

pose now may l a t e r prove to be of l i t t l e re levance; t h e r e f o r e , I suggest an

i n t e r a t i v e approach in which i n i t i a l s t u d i e s he lp to quant i fy a prel iminary

model to provide guidance on which a r e the w e t important next s teps .

A model is a conceptual t o o l t h a t i n t e g r a t e s a s e t of hypotheses about

how t h e system w r k s a t a fundamental l e v e l . Such a t o o l can be used to

guide r e sea rch , r e f i n e our understanding of t h e system, f a c i l i t a t e c o p

munication between i n v e s t i g a t o r s and managers, and, f i n a l l y , combine a l o t

of d i v e r s e q u a n t i t a t i v e information about t h e system in to an evalua t ion of

p o s s i b l e impacts. I envis ion r e l a t i v e l y simple energy budgets of the major

subsystems and simple growth w d e l s of one o r two spec ie s (i .e. , hogchoker

and anchovies) f o r which ice propose a d i f f e r e n t s e t of s a l i n i t y optima,

varying by l i f e s t age , and which we expose to var ious t i m e varying s a l i n i t y

regimes s imula t ing w n d i t i o n s in the various segments of the r i v e r under

d i f f e r e n t water management opt ions .

1. Primary Producers

^ .' A knowledge of t h e p r i n c i p a l types of primary producers of t h e r iver-

t h e i r a r e a l coverage, requirements , growth dynamics, and n u t r i e n t uptake,

s t o r a g e , and r e l e a s e rates is e s s e n t i a l to eva lua t ing the poss ib l e response

o f the r i v e r to decreased f l o v r a t e s o r increased inpu t s of n u t r i e n t s from

t h e watershed. I have divided the primary producers i n t o ca t egor i e s , a s

fo l lows , based on c e r t a i n c h a r a c t e r i s t i c s of t h e i r connection with the

r i v e r . Upland p lants : c o n t r i b u t e o rgan ic d e t r i t u s t o r i v e r in w o f f i n pro-

po r t ion to r a i n f a l l , which in f luences both the amount of p l an t biomass pro-

duced and the proport ion of above-ground biomass t r anspor t ed to the r i v e r .

Bank o r canopy: t r e e s , v ines , and shrubs on banks o r d i n a r i l y not flooded.

Canopy coverage of t h e r i v e r determines t h e d i r e c t input of l ea f d e t r i t u s

and a l s o the suppression of photosynthes is by phytoplankton and submerged

p lan t s .

Seasonally-flooded vegetat ion: c o n t r i b u t e o rgan ic m a t e r i a l t o t h e r i v e r

and t ake up n u t r i e n t s from the water c o l u w on ly during the times of year

when water l e v e l s a r e excep t iona l ly high.

I n t e r t i d a l emergent vegetat ion and periphyton: c o n t r i b u t e s t o r i v e r food

cha ins , is u t i l i z e d a s f i s h and macroinver tebra te h a b i t a t , and t akes up

n u t r i e n t s only when i t is f looded, which occurs only p a r t of t h e day.

Continuously-flooded emergent vegeta t ion and periphyton: c o n t r i b u t e s t o

r i v e r food chains, is u t i l i z e d a s f i s h and macroinver tebra te h a b i t a t , and

t a k e s up n u t r i e n t s wnt inuous ly .

Submerged p l a n t s and epiphytes: c o n t r i b u t e t o r i v e r food chains, take up . " . n u t r i e n t s wn t inuous ly ; l i g h t recept ion can be a f f e c t e d by canopy coverage

and phytoplankton dens i ty .

Phytoplankton: c o n t r i b u t e to r i v e r food chain and take up n u t r i e n t s wn-

t i nuous ly ; r a t e of s inking inve r se ly p ropor t iona l to r i v e r flow; r a t e of

removal from r i v e r d i r e c t l y p ropor t iona l t o r i v e r flow; l i g h t t ransmission

t o submerged p l a n t s is inve r se ly p ropor t iona l t o phytoplankton dens i ty .

Subdiv is ions within each of these c a t e g o r i e s sepa ra t e the major growth

forms (1.e. g r a s s e s and sedges from mangroves) end spec ies .

Table 1 g ives a very rough approximation of t h e percent r i v e r a rea

covered by each of t hese vegetat ion types (except upland, of course) in

each of the r i v e r zones. These a r e my very gross e s t ima tes from qua l i t a -

t i v e information in the l i t e r a t u r e . A r igorous examination of information

from the vegeta t ion t r a n s e c t s would y i e l d m r e accura t e e s t ima tes . S t i l l

more accura t e e s t ima tes w u l d be obtained by us ing the information from the

t r a n s e c t s in combination with a e r i a l photographs t o map t h e r i v e r by vege-

t a t i o n type. A s p e c i a l p r o j e c t would be necessary to adequately map the

seag ras s beds of Myakka Bay and Upper Char lo t t e Harbor.

During t h e Phase I1 study, t h e concent ra t ion of ch lorophyl l a was

h ighes t in the lower p a r t of the r i v e r (zone 4 ) and nex t h ighes t in the

upper r i v e r (zone 1). Lowest w n c e n t r a t i o n s occurred in zone 2. Submerged

vegeta t ion is most prevalent below E l Jobean ( i n Zone 4 ) , and then only in

very ahallow water. The ex ten t of wverage by bottom vegeta t ion in Myakka

Bay is n o t known and w u l d be s i g n i f i c a n t . Mangrove area is most extens ive

Table 1. Estimated percent river area covered by various primary producers, by zone.

. " ..

Tot Seasonally Continuously Emergent Flooded Intertidal Flooded Submerged Submerged Phyto-

Zone Canopy Vegetation Vegetation Veg . Veg . Veg. plankton

a Spartina bakerii

b Scirpus

C Juncus

Red mangrove

Black mangrove

Note: Zonation scheme is river width. Phytoplankton was calculated as total river area minus canopy area.

i n zone 4. Emergent vegetat ion i s imst ex tens ive in zone 3, which inc ludes

t h e braided r i v e r sec t ion . ~ h ; r e is no mangrove, l i t t l e emergent vegeta-

t i o n , and only l imi t ed submerged vegetat ion in zone l. ^ . '

The a rea covered by d i f f e r e n t types of primary producers plays an

important r o l e in the n u t r i e n t dynamics of the r i v e r . Knowing the r e l a t i v e

coverage by var ious types of primary producers might he lp in i n t e r p r e t i n g

n u t r i e n t da ta . For in s t ance , the observed dec l ine in inorganic n i t rogen con-

c e n t r a t i o n s between U.S. 41 and E l Jobean noted in Phase I1 sampling might

be due to the r e l a t i v e l y high coverage of the r i v e r by emergent vegeta t ion

i n t h e braided r i v e r sec t ion . Improving our e s t ima tes of a r e a l coverage by

t h e var ious primary producers is important i n determining the poss ib l e

response of the r i v e r to increased inpu t s of n u t r i e n t s and organic ma te r i a l

t h a t might r e s u l t from an upstream waste water r ecyc l ing f a c i l i t y .

Secondary p roduc t iv i ty by the ben th ic community i s fueled by o rgan ic

ma te r i a l . The primary producers a r e the sources of o rgan ic ma te r i a l to the

system. Table 2 shows my very g ross e s t ima tes of the percent of t o t a l

energy a s o rgan ic ma te r i a l cont r ibuted to the r i v e r by primary producers of

var ious types. These e s t ima tes suggest t h a t t h e propor t ion of o rgan ic

m a t e r i a l cont r ibuted by t h e var ious types of primary producers probably

d i f f e r s by r i v e r zone. Some of t h e d i f f e r e n c e in the dens i ty of benth ic

organisms between zones may be due to t h e d i f f e r e n c e in sources and quan-

t i t i e s of o rgan ic m a t e r i a l a v a i l a b l e to t h e benthos in t h e var ious zones.

Submerged a q u a t i c vegeta t ion c o n t r i b u t e s t o the d isso lved oxygen of

r i v e r bottom waters. Knowing the e x t e n t of coverage by SAV i n each zone

w i l l help us t o eva lua te the importance of t h i s con t r ibu t ion to the DO con-

t e n t of bottom waters in each zone.

Table 2. Estimated percent total organic matter from indicated source, by river zone.

Emergent Submerged Upland Vegetation Vegetation - . . Zone Detritus & periphyton & epiphytes Phytoplankton -

Note: Zonation scheme is river width.

2. Dominant F i s h Species and Trophic S t r u c t u r e

The dominant f i s h spec ies-of the r i v e r during Phase I (wet season) and

Phase I1 (d ry season) sampling a r e shown in Table 3. The percent of t o t a l

-specimens in samples each r e p r e s e n t s is given. These spec ie s probably s r e

t h e major higher consumers of the r i v e r , a l though some major consumers may

n o t be included here because they a r e d i f f i c u l t o r impossible to ca t ch in

t rawls . By determining the p r i n c i p a l prey of these spec ie s , we can iden-

t i f y t h e major pathways of energy flow t o the major consumers.

Stomach contents a n a l y s i s was not included in e i t h e r the Phase I o r

Phase I1 s t u d i e s , however the d i e t a r y h a b i t s of many of these spec ie s in

o t h e r a r e a s is a v a i l a b l e from o t h e r s tud ie s . Table 4 l is ts t h e prey com-

p o s i t i o n of Uyakka dominants t h a t were covered by Carr and Adams (1973) a t

C r y s t a l River , F lo r ida . Also included to f i l l gaps o r provide a d d i t i o n a l

pe r spec t ive is information from Odum and Heald (1972) a t North River in

Everglades National Park and Darnel l (1958) a t Lake Ponchar t ra in , Louisiana.

Included a r e p in f i sh . bay anchovy, s p o t , p i g f i s h , b g f i s h , s i l v e r perch, sea

c a t f i s h , hardhead c a t f i s h , s p o t f i n m j a r r a , and s t r i p e d m j a r r a . Pink

shrimp i s a l s o included. The t a b l e i n d i c a t e s t h a t copepods and amphipods

can be u t i l i z e d by many of these species . P lanktonic copepods a r e par-

t i c u l a r l y important in the d i e t s of very young f i s h , most of which feed in

t h e water column. Caridean shrimp, polychaetes , and molluscan ve l ige r l a r -

vae can be heavi ly u t i l i z e d by some o f these spec ie s .

Although A. m i t c h i l l i a t Crys t a l River fed almost e n t i r e l y on copepods - and molluscan ve l ige r l a rvae . t h i s spec ie s consumed a wider v a r i e t y of prey

a t North River and a l s o a t Lake Pon tcha r t r a in (Darnel l 1958) w d a t Tampa

Bay (Spr inger and Woodburn 1960). Mysids were an important component of

Table 3 . Major Fish Species of the Myakka River. I

Percent Total Fish . - .' Phase I Phase I1 Spawning

a wet b Season

Trinectes maculatus (hogchoker) 30 8 1 S m (May-Nov)

Leistomus xanthurus (spot)

Micropogonias undulatus (croaker)

Anchoa mi tchi l l i (bay anchovy)

Lagcdon rhomboides (pinf ish)

Bairdiella chrysoura ( s i lver perch)

Cynoscion arenarius (sand seatrout)

Orthopristis chrysoptera (pigf ish)

Symphurus plagiusa

Menticirrhus - americanus (kingfish)

Arius f e l i s (sea ca t f i sh ) -- Bagre marinus (hardhead)

Diapterus sp.

Eucinostomus argenteus (mojarra)

6

3 Win-Early Spr

2 Win-Early Spr

2 Il'in-Early Spr

1

1 Spr-Sum

1 Win-Early Spr

1

Spr 4 Sum

a Total dry-season f i s h catch was 662 (30 species)

b Total wet-season f i s h catch was 1,241 (22 species)

Table 4. Stomach contents a s various prey taxa, s p e c i f i c to s i z e of predator taxa, according t o various indicated l i t e r a t u r e sources. Values a r e percent dry weight o r percent volume.

Mollusc P lan t Veliger Harpact. Caridean Penaeid Amphi- Iso- bs t ra- POIT-

Algae Detri Larvae Copepods Copepods W s i d s Shrimp Shrimp pods pods coda chaetes Lagodon rhomboides

10-20 mm (a) 70-85 21-35 mm (a) 36-60 mm (a) 65-80

30-40

61-80 mm (a) 20-35 5-15 10-25-- 81-110 mm (a) 5-10 5-10

Anchoa m i t c h i l l i 1 5 - 2 3 - 50-74 26-50

31-36 mm (b) 11 9 19 22 L e i o s t o m s xanthurus 10

40-99 mm (f) 27(g) 6(h) 11 1 8 8 27(g)

13 100-149 mm ( f ) 1 9 10

2 ( i )

38(g) 1

150-203 mm ( f ) 7 12 O r t h o p r i s t i s e)

31-50 mn (a) 40-50

51-80 mm (a) 20-35 3-1 2 5-30

25-85 T r i n e c t e s maculatus

18-35 mm (a) B a i r d i e l l a chr soura 60-90

6-15 mm (a -?- 16-40 mm (a) 41-160 mm (a) l a rvae (b) 127-181 mm (b)

Ar ius f e l i s -- 205-331 mn (b)

marinus 262-445 mm (b)

Eucinostomus a r en teus 19-63 mm (b +-- dry season (b) 6 39 7 3 1

5 wet season (b) 9 38 6 Diapterus lumieri

35-172 mm 5-7- b 4 4 44 36 3 Penaeus duorarum ( e ) X X X X

Table 4. (Continued)

Xanthid Blue Chiron. Fish Zoo- Sand tb. Stom . Crabs Crab Molluscs Larvae Larvae F i sh plank Grains with Food

Lagodon rhomboides 1,608 10-20 mm (a) 21-35 mm i a j 36-60 mm (a) 61-80 mm (a) 81-110 mm (a)

Leiostomus xanthurus 40-99 m ( f )

O r t h o p r i s t i s

Tr inec tes maculatus 18-35 mm (a)

B a i r d i e l l s chr soura 6-15 imm (a -i-- 16-40 nun (a) 41-160 mm (a) la rvae (b) 127-181 mm (b) . ~

Arius f e l l s - 205-n (b)

. ~

Eucinostonus a r enteus 19-63 mm (b ?-- dry season (b) wet season (b)

Dispterus lumieri 35-172 mm 9-r b

Penaeus duorarum (e)

Table 4. (Continued)

(a) Values a r e percent dry weight from Carr and Adams (1973). (b) Values a r e percent mlume from Odum and Heald (1972). (c) The f i s h was Anchoa m i t c h i l l i . (d) The xanthid crab was Rithropanopeus h a r r i s i i . ( e ) Non a u a n t i t a t i v e observat ions from Sastrakusumah (1971). i f j v a l u A a r e percent volume from Darnel l (1958). (g) Copepods t h a t could not be i d e n t i f i e d to Harpacticoid o r otherwise. (h) Includes "undetermined organic matter" a s well a s "detr i tus". ( i ) I d e n t i f i e d only aa "Annelid." Included with polychaetes in t h i s tab le . (j) P r i n c i p a l l y Rangia cuneata.

t h e d i e t of bay anchovy a t Lake Pon tcha r t r a in , making up from 28 t o 52% of

stomach contents by volume. F i s h were important in the d i e t of l a r g e r

ind iv idua l s , comprising 33% of stomach contents wlume of A. m i t c h i l l i - * .'

60-74 mm in length. Darnel l concluded t h a t the bay anchovy had two ontoge-

n i c feeding stages: very young f i s h feeding in the water column and o lder

f i s h feeding on the benthos. Polychaetes, the p r i n c i p a l benthic taxa found

i n the stomachs of o the r f i s h species , were absent from the stomachs of A. - m i t c h i l l i taken in the Ten Thousand I s l a n d s by Colby e t a 1 (1985).

Zooplankton made up approximately 50% by weight of stomach contents of a

l a r g e c o l l e c t i o n of A. m i t c h i l l i in a wide range of s i zes . - The p r i n c i p a l d i e t of hogchoker a t Crys ta l River was polychaetes (Carr

and Adams (1973) (Table 4). Hildebrand and Schroeder (1928), examining 17

f i s h from Chesapeake Bay, concluded t h a t T. maculatus fed pr imar i ly upon - anne l ids , supplemented by occas ional small crustaceans and s t r ands of

a lgae . Darnel l (19581, f ind ing t h r e e ou t of 10 hogchokers with recogni-

z a b l e food in t h e i r stomachs, determined that amphipods of the genus

Corophium were present I n a l l t h ree and made up about 50 percent by volume

o f contents . hdeter rn ined organic matter and d e t r i t u s comprised the

remainder. Examination of i n t e s t i n a l contents revealed t h a t the hogchokers

had a l s o consumed o t h e r microcrustaceans, chironomid l a rvae , foramini fera ,

and seeds. Reid (1954) examined the stomaches of 8 hogchokers a t Cedar Key

but found a l l of them empty except fo r sand. In exclosure s t u d i e s in

Chesapeake Bay, Virns te in (1977) discovered t h a t hogchokers had no appre-

c i a b l e e f f e c t on the dens i ty of an infauna cons i s t ing p r i n c i p a l l y of poly-

chaetes , but he based t h a t conclusion on only one f i s h . The number of hog-

chokers in each of these s t u d i e s was s m a l l . A l a r g e r sample and s i z e range

of bogcboker should be examined to adequately understand the d i e t of t h i s

species .

.' My review of stomach contents s t u d i e s of both the bay anchovy anh

t h e hogchoker l ed me to the opinion t h a t stomach contents s t u d i e s of a

s p e c i e s need to be conducted i n an a rea where the s p e c i e s is mst abundant

as well a s where it is sca rce to adequately understand the d i e t of the spe-

c i e s . If r e l a t i v e number of samples obtained f o r stomach contents a n a l y s i s

provide even a rough index of t h e r e l a t i v e abundance of a spec ies , then b g -

chokers occurred in low abundance r e l a t i v e to o t h e r spec ies in the a reas

where stomach contents s t u d i e s were conducted. Cer t a in ly t h e abundance of

t h i s spec ies r e l a t i v e t o o t h e r spec ies in the Myakka River is g r e a t e r than

in the a r e a s where stomach contents analyses were conducted, and stomach

contents analyses w u l d have to be conducted here to adequately understand

t h e i r d i e t in t h i s system.

According to t h i s cursory overview, a l l of t h e major f i s h spec ies of

t h e Myakka River feed on benth ic inve r t eb ra te s . A t e a r l y l i f e s t a g e s , many

feed in the water column-on copepods. Both infaunal organisms and epi-

faunal c rus taceans appear to be important d i e t a r y i tems of the Myakka River

f i s h species. P r i n c i p a l prey i tems o f the Myakka River f i s h community, a s

suggested by examination of the same spec ies in o t h e r a r e a s , a r e summarized

i n Table 5. I f t h e feeding h a b i t s of these spec ies in the Myakka River a r e

s i m i l a r to t h e i r h a b i t s elsewhere, then the major pathway o f energy flow to

higher consumers of Myakka River is through t h e benthos.

3. Density and Biomass Density of F i s h and t h e Benthos

F i s h a r e a conspicuous component o f t h e ecosystem, and f i s h i n g , both

Table 5. Principal prey taxa of major fish species of the Myakka River.

Copepods

Harpacticoid copepods

Mysids

Caridean shrimp (Palaemonetes)

Penaeid shrimp

Polychaetes

Mollusc veliger larvae

Amphipods

Isopods

Plant detritus

Algae

Fish (Eucinostomus sp. and Anchoa mitchilli

i n the Myakka River and in Char lo t t e Harbor, a r e important commercial and - r e c r e a t i o n a l a c t i v i t i e s . Nine spec ies during dry season and 14 spec ies

"during wet season were i d e n t i f i e d in Phase I and Phase I1 r e p o r t s as .the

dominant f i s h spec ies of the r ive r . The p r i n c i p a l spec ies is the

hogchoker, which made up SO and 30 pe rcen t of f i s h caught in dry-season and

wet-season sampling, r e spec t ive ly . A comparison of the change in hogchoker

d i s t r i b u t i o n on various s t ages of the t i d e (Table 8 ) sugges ts t h a t they do

n o t move out i n t o Char lo t te Harbor: t o feed-even during the season and t i d e

when s a l i n i t i e s a r e lowest there. Hogchoker d e n s i t i e s were c o n s i s t e n t l y

lower a t the Upper Char lo t t e Earbor s t a t i o n than a t upstream s t a t i o n s

throughout a l l t i d a l cycles. Lower d e n s i t i e s of b g c h o k e r a t the m u t h

of t h e r i v e r may have been due to the f a c t t h a t the bottom i s anoxic a t the

r i v e r mouth during periods when s a l i n i t i e s in Char lo t t e Harbor a r e lower

than in the upper r i v e r (E. Estevez, pers . comm.). I f , however, t h i s spe-

c i e s is p r imar i ly dependent upon the r i v e r , then hogchoker d e n s i t i e s m i g h ~

provide a good index of the o v e r a l l eco log ica l well-being of the r ive r .

Seasonal va r i a t ion in dens i ty due to spawning p e r i o d i c i t y m u l d have to be

a cons idera t ion in us ing bgchoker d e n s i t i e s a s an ind ica to r of the

environmental hea l th of the r ive r .

My a n a l y s i s o f the food h a b i t s of these spec ies according to s t u d i e s

i n o t h e r a r e a s suggested t h a t , beyond the p lanktonic p o s t l a r v a l s t a g e ,

almost the e n t i r e ene rge t i c support of the f i s h cormnunity comes from the

benthos. Meanwhile, ben th ic core sampling suggested t h a t the dens i ty of

ben th ic organisms was extremely low in the upper and braided por t ions of

t h e r i v e r . The a r e a s o f these two r i v e r zones ( 1 and 2 ) are r e l a t i v e l y

smal l compared to t h a t o f t h e lower r i v e r (zones 3 and 4), which comprise

Myakka Bay and Upper Char lo t t e Harbor. My rough es t ima tes suggest t h a t

r i v e r a rea in zones 3 and 4 i s - a t l e a s t 10 t imes g r e a t e r than t h a t in zones

1 and 2 (Table 6). The low benth ic dens i ty coupled with the l o w a r e a l

^ .' . coverage of the two upper r i v e r zones sugges ts t h a t the f i s h community is

s t r o n g l y dependent upon the lower r i v e r f o r i ts food.

Benthic core samples a t the f i v e s t a t i o n s may not adequately r ep resen t

ben th ic animal d e n s i t i e s in any of the zones. Zone 2 conta ins considerable

a r e a of sa l twa te r marsh, which probably was not covered by benthic core

sampling, Zone 1 Lontains some freshwater marsh t h a t i s possibly important

i n food chains , but t h i s a rea probably was not covered e i t h e r . On t he

o t h e r hand, t h e seagrass beds in zones 3 and 4 may not have been sampled

wi th ben th ic cores in proport ion to t h e i r a r e a l coverage of these zones.

Benthic sampling s t r a t i f i e d by h a b i t a t is e s s e n t i a l to making good estima-

t e s o f the r e l a t i v e abundance of benth ic organisms in the d i f f e r e n t sec-

t i o n s of the r ive r .

F i s h d e n s i t i e s and benthos d e n s i t i e s in the r i v e r were not w e l l corre-

l a t ed . Benthos d e n s i t i e s were h ighes t a t s t a t i o n T-53, whereas f i s h den-

sities were h ighes t a t s t a t i o n T-40. F i s h d e n s i t i e s a t s t a t i o n s T-7 and

T-19 did n o t r e f l e c t the l o w benthic d e n s i t i e s there . H6gchokers. i n par-

t i c u l a r , were found a t f a i r l y high d e n s i t i e s a t these s t a t ions -

p a r t i c u l a r l y on f looding and high t i d e s . Hogchoker d e n s i t i e s a r e , in f a c t ,

a s high a t these s t a t i o n s a s a t T 4 0 . Poss ib ly the benthic core samples do

no t adequately represent r e l a t i v e dens i ty of benthos in Zone I. Alterna-

t i v e l y , perhaps high predat ion p ressu re by hogchokers is maintaining the

ben th ic connuunity in a s t a t e of low dens i ty and high product iv i ty . But i s

t h i s poss ib le? Nichols (1977) and o t h e r s have observed t h a t the r a t i o of

production to biomass in benth ic communities is f a i r l y constant a t around

4.5. Ooe would expect the r a t i o o f production to dens i ty t o be, i f

anything, even mre s t a b l e . F u r t h e r m r e , f i s h dens i ty and, presumably pre- .. .' *

da t ion pressure , was grea te r a t T-40 a s a t s t a t i o n s T-7 and T-19, s i n c e

f i a h dens i ty was g r e a t e r st T-40, y e t the dens i ty of benth ic organisms was

s i x times g r e a t e r there!

Even i f t he food supply f o r f i s h in the braided and upper r i v e r zones

i s small i n comparison to t h a t of the lower r i v e r , t hese a r e a s might be

e s s e n t i a l t o t h e f i s h community i f they contain c r i t i c a l h a b i t a t f o r f i s h

a t l a t e p o s t l a r v a l and e a r l y se t t lement s tages. Herke (1971), Hansen

(1969), and o t h e r s suggest t h a t salt marshes and t i d a l creeks in extremely

l o r s a l i n i t y (1,-5 ppt ?) por t ions o f e s t u a r i e s may be critical h a b i t a t f o r

estuarine-dependent f i s h when they f i r s t s e t t l e ou t of the plankton. Red

drum, spo t , snook, and Aclant ic croaker a r e four spec ies f o r which an

occurrence of very small i nd iv idua l s in waters o f s a l i n i t i e s below 5 ppt

can be documented. The s i z e d i s t r i b u t i o n of hogchokers and bay anctmvy

wi th d i s t a n c e upr iver suggests t h a t these spec ies , too , use very low s a l i -

n i t y p a r t s of the r i v e r a s nursery grounds.

The perpetua t ion of f i s h s tocks in the r i v e r and poss ib ly in Char lo t t e

Harbor and o f f shore , a s well, is dependent upon su rv iva l and growth of

e a r l y l i f e s t ages , which determines recru i tment to t h e i r populat ions. The

importance o f various s p e c i f i c types of h a b i t a t s in the braided and upper

r i v e r zones to e a r l y l i f e - s t age f i s h e s needs t o be determined. An inves t i -

ga t ion of the spec ies composition and dens i ty o f f i s h in the s a l t marshes

a s soc ia t ed d t h and mnnected to t h e braided and upper por t ions o f the

r i v e r may provide important information r e l evan t to t h i s question.

4. Zones and Zonation Schemes

The study group divided the r i v e r in to zones based on s e v e r a l d i f - " .' . f e r e n t sets of c r i t e r i a . b e approach to a s s i m i l a t i n g the Phase I and

Phase I1 r e p o r t s was to examine and compare the zones r e s u l t i n g from the

d i f f e r e n t zonation schemes. Addi t ional ly , I use da ta from benthic core and

t r a w l sampling to es t imate zonations on the b a s i s of r e l a t i v e d e n s i t i e s .

The r i v e r was divided by r i v e r width i n t o the fol lowing four zones:

Zone 1 ( t r a n s e c t s 1-15) 0-250': narrow, with s t e e p banks

Zone 2 ( t r a n s e c t s 17-34) 250-1,000': "braided r i v e r " , s t r e t c h having g r e a t e s t a s soc ia t ed marshes

Zone 3 ( t r a n s e c t s 35-44) 1,000-3,500': Myakka Bay (mangrove f r i n g e )

Zone 4 ( t r a n s e c t s 46-53) 3,500-13,500': Upper Char lo t t e Harbor (mangrove f r i n g e )

I found t h i s scheme convenient to use s ince shore l ine length and the

range of r i v e r width in each o f these zones was given in the Phase I

r e p o r t . I used t h i s information t o ob ta in a rough es t imate of the r e l a t i v e

a r e a of each zone (Table 6). Q u a l i t a t i v e d e s c r i p t i o n s suggest t h a t the

p r o p o r t i o n a l i t y of various aqua t i c h a b i t a t s ( i . e . , submerged p l a n t s ,

emergent vegeta t ion , mangroves) may be oore s i m i l a r wi th in each of these

zones than between them.

A zonation scheme roughly based on s a l i n i t i e s was given a s follows:

Upper r i v e r , u s u a l l y < 1 pp t s a l i n i t y during both wet and dry seasons.

Mid r i v e r , u sua l ly < 1 pp t during wet season and 1-10 ppt during dry season.

Lower r i v e r , u sua l ly 5-20 ppt during w e t season and 15-22 ppt during dry season.

Delineat ion of these zones by the s tudy team apparent ly i s mdergoing

Table 6. Area of r i v e r , by zones of i n d i c a t e d width range, a s es t imated from width range and s h o r e l i n e l ength i n Phase I report .

- E s t .

Width West East Width Area Zone Transect Range ( f t ) Bank ( f t ) Bank ( f t ) Used i t2

I 1-15 0-250 29,852 31,875 50 1 , 4 9 2 , 6 0 0

continuous r ev i s ion a s da ta from new monthly surveys is obtained. For t h i s . reason, p r e c i s e boundaries a r e not given in the r e p o r t s , making it di f -

_ . f i cu l t to mmpare t h i s zonation scheme with o the r s . The a rea of the s i v e r

exper iencing 1-4 ppt s a l i n i t i e s during the wet season was not included in

t h i s zonation scheme. Perhaps it should be i d e n t i f i e d a s a separa te zone.

Information on vegetat ion communities along the banks of t h e r i v e r

were used to c l a s s i f y the r i v e r in to t h r e e zones. In order to f a c i l i t a t e

comparison with o the r zonation schemes, the zone numbers a r e changed from

those given in the t ex t .

Zone &e, a r i v e r i n e community - from r i v e r mile 13.0 t o 21.0. (roughly, Transects 1-9). r a r e l y experiences s a l i n i t i e s > 1 ppt .

Zone Two, a t r a n s i t i o n a l m m u n i t y - from r i v e r mile 6.0 t o 13.0. (roughly, Transects 10-33)

Zone Three, an estuarine/marine community - from r i v e r mile 2.3 t o 6.0 (measured from C a t t l e Dock Point near the o u t l e t to Char lo t t e Harbor)

(roughly, Transects 34-53), r a r e l y experiences s a l i n i t i e s < 1 pp t .

The vegetat ion zonation i s on the b a s i s of c l u s t e r i n g vegetat ion

communities from 20 s i t e s from both s i d e s o f the r i v e r according to

Czekanowski's index of percent s i m i l a r i t y . Complicating f a c t o r s in the

a n a l y s i s were caused by wmmunity d i f f e r e n c e s on opposi te s ides of the

r i v e r , poss ib ly occur r ing due to d ischarges of freshwater from t r i b u t a r i e s

emptying p r imar i ly i n t o the e a s t s ide. The vegetat ion communities probably

r e f l e c t long-term s a l i n i t y condit ions.

The r i v e r was a l s o zoned according to c a m u n i t i e s o f submerged aqua t i c

vegeta t ion (SAV). These zones were as follows:

Zone I, freshwater SAV, i d e n t i f i e d by presence of E leochar i s ba ldwini i , Ceratophyllum demersum, N i t e l l a sp., or subu la ta and, poss ib ly , t he absence of

one oxbow.

Zone 11, low s a l i n i t y SAV; i d e n t i f i e d by presence of V a l l i s i n e r i a .

Zone 111, brackish SAV, i d e n t i f i e d by dominance of Ruppia. - ,' *

Zone I V , marine SAV, i d e n t i f i e d by dominance of Diplsnthera.

Zone I i s discontinuous, i n t e r rup ted by Zone 11. The upper s t r e t c h of Zone

I inc ludes Transects 1-7. Its lower s t r e t c h encompasses Transects 18-25.

The lower freshwater zone is apparent ly due to the inflow of water from

Deer P r a i r i e Creek. Zone I1 encompasses Transects 8-17. Zone 111 includes

Transec t s 26-40. Apparently the freshwater inflows from Big Slough a r e not

s u f f i c i e n t to c r e a t e freshwater cond i t ions in t h i s s t r e t c h . Zone I V inc lu-

des Transec t s 41-53. A t r a n s i t i o n SAV community from Transec t s 19-38 was

i d e n t i f led.

According to annel id d i s t r i b u t i o n s during the wet season (September

sampling) a t f i v e t r a n s e c t s t a t i o n s , t h e r i v e r can be divided in to th ree

zones:

Upstream, < 1 pp t s a l i n i t y (T-7, T-19, T-27)

Mid region, 6-12 pp t (T-40)

Downstream, gene ra l ly 6-18 ppt (T-53)

Based on mollusc d i s t r i b u t i o n s during both the wet and the dry season

t h e r i v e r was divided in to t h r e e zones. I have changed to an alphaneumeric

numbering to prevent confusion with o the r zonal des ignat ions .

Zone A, l i w e t i c (< 1 ppt s a l i n i t y ) , (upstream of T-13)

Zone B, o l igoha l ine to mesohaline (approximately 1-15 p p t )

(roughly, T-14 through 36)

Zone C, meso-polyhaline (approximately 15-25 p p t ) , (T-37-53)

Zone A was sa id t o be charac ter ized by the presence of Corbicula manilen-

sis. Zone B was I d e n t i f i e d as- being the a r e a o f g r e a t e s t osmotic s t r e s s , - being subjec ted to the g r e a t e s t s a l i n i t y f l u c t u a t i o n s . Two tam, Tagelus

-p lebius and Polymesoda c a r o l i n i a n a , may c h a r a c t e r i z e t h i s area. Zon' C was

c h a r a c t e r i z e d by a much higher d i v e r s i t y of w l l u s c taxa than was found a t

Zones A and B. The region between t r a n s e c t s 5 and 34 exh ib i t ed very low

molluscan d i v e r s i t y and s high proport ion of empty w l l u s c s h e l l s ,

sugges t ing a dynamic community with r e s p e c t to s a l i n i t y and a region of

t r a n s i t i o n between l i w e t i c and " t rue" e s t u a r i n e condi t ions . The empty

mollusc s h e l l s suggested t h a t the w l l u s c a n s p e c i e s s h i f t e d back and f o r t h

wi th changing s a l i n i t y cond i t ions on the inner boundaries of t h e i r s a l i n i t y

ranges.

Based on crustacean d i s t r i b u t i o n s during the ve t season, the r i v e r was

divided in the Phase I1 r e p o r t i n t o two zones, l abe led zones B and C t o

conform t o the zones def ined by mollusc d i s t r i b u t i o n s . Zone B of the

crus tacean d i s t r i b u t i o n extends i n t o zone A of t h e m ~ l l u s c i i i s t r i b u t i o n .

Crustacean d i s t r i b u t i o n s ind ica ted a " t r a n s i t i o n region" extending from

s t a t i o n T-9 through T-44, the region from T-9 through T-25 appearing par-

t i c u l a r l y "stressed".

Table 7 , compiled from the Phase I r e p o r t , shows t h e r e l a t i v e dens i ty

o f benthos, by major taxa, a t f i v e r i v e r s t a t i o n s , according to

b e n t h i c co res , t he only q u a n t i t a t i v e sampling method used on t h e benthos.

I f on ly these da ta a r e used, it appears t h a t a zone of low benth ic dens i ty

from at l e a s t s t a t i o n T-7 through a t l e a s t s t a t i o n T-27 can be

d i s t ingu i shed . Benthic d e n s i t i e s a r e approximately s i x times g r e a t e r a t

T 4 0 and approximately 10 t imes g r e a t e r a t T-53 than a t T-7. T-19, and

Table 7. Relative densities df benthos and fish from Phase I report.

. * .. A. Relative abundance of benthos, by major taxa, at five river stations,

from benthic core sampling, September, 1985.

1 2 3 4 5 Taxa (T-7) (T-19) (T-27) (T-40) (T-53) Tot

Molluscs 10 1 15 73 145 244

Crustaceans 10 35 64 10 5 608 820

nnnelids 38 6 10 14 4 420 668

Tot

8 . Number of fish and macroinvertebrate individuals taken in trawls, September, 1985.

Night 463 745 224 2,081 1,049 4,562

Tot 945 799 289 3,667 1,328 7,028

-

T-27. S t a t i o n T-53 i s in Upper C h a r l o t t e Narbor. T-40 i s in bwer Myakka

Bay. T-27 i s in the braided r l v e r area. T-19 i s in the "shallows" a rea

upstream of Deer P r a i r i e Park. T-7 is upr iver near Snook Haven. "... *

Also shown in Table 7 i s the number of f i s h taken in o t t e r t r awls

dur ing September sampling a t f i v e s t a t i o n s corresponding t o the loca t ion of

t h e ben th ic co re sampling. These da ta suggest t h a t f i e h dens i ty is lowest

a t s t a t i o n T-27 and in termedia te a t T-7 and T-19. The h ighes t f i s h dens i ty

was found a t T-40. Some f i s h s p e c i e s a r e found p r imar i ly downriver,

whereas o t h e r s a r e found p r imar i ly upr iver . The hogchoker is found both

upr ive r and downriver, d e n s i t i e s being approximately equal a t T-7, T-19,

and T-40 (Table 8). Hogchoker a r e less abundant a t t he mid-river s t a t i o n ,

T-27, than a t e i t h e r up r ive r o r downriver s i t e s . Hogchoker d e n s i t i e s drop

s h a r p l y below T-40 and a r e extremely low a t the w u t h of the r i v e r (T-53).

The d i s t r i b u t i o n o f hogchoker changes somewhat with the t i d e , and d e n s i t i e s

a r e higher up r ive r on the high t i d e . But, r ega rd les s of t i d e , hogchoker

d e n s i t i e s a r e lower a t s t a t i o n s T-27 and T-53 than elsewhere. The f a c t

t h a t d e n s i t i e s a r e extremely low a t the w u t h of the r i v e r , even on

outgoing t i d e s dur ing the wet season, sugges ts t h a t t h i s spec ies may not

l e a v e the r i v e r . The s p a t i a l d i s t r i b u t i o n of hogchoker may be w r t h exa-

mining more c lose ly . I f t h i s spec ies seldom o r never leaves the v a k k a

River , it might an i d e a l organism to m n i t o r a s an i n d i c a t o r of condi t ions in

t h e r i v e r .

The r i v e r was divided in to the fol lowing zones according to the

d i s t r i b u t i o n o f f i s h eggs and la rvae:

Upriver (< 5 p p t ) , f reshwater s p e c i e s

T r a n s i t i o n , low d i v e r s i t y and abundance

Table 8 . Bogchoker c a t c h e s i n t r a w l s during Phase I (September 1985) sampling.

. S t a t i o n

Tide 6 1 2 3 4 5 Day o r Night T-27 T-19 T-27 T-40 T-53 T o t

Day ebb

Day f l o o d

Day s l a c k t i d e

Day s l a c k low

Night ebb

Night f l o o d

Night s l a c k h i g h

Night s l a c k l o w

Tot

Lower r i v e r (>= 5 p p t , e s t u a r i n e s p e c i e s

The Tarpon P o i n t s t a t i o n , which is l o c s t e d near Transect S ta t ion 33 ( a t

r i v e r mile 8.7) was descr ibed a s epi tomizing t h e t r a n s i t i o n area . It

seemed t o be a d i v i d i n g line between freshwater m d e s t u a r i n e forms ds r ing - .' both the wet and t h e dry seasons. The a rea between Myakka Bay aud Deer

P r a i r i e Creek, which mcompasses the Tarpon Point s t a t i o n , was r e f e r r e d to

as t h e "wet season es tua ry" with r e spec t t o l a r v a l f i s h . Th i s des ignat ion

was no t explained. It seems to me that t h i s region might more a p t l y be

desc r ibed a s the "dry season es tuary" , because e s t u a r i n e s a l i n i t i e s extend

f u r t h e r upstream during the dry season than during the we t season. Perhaps

t h e "wet season" des ignat ion was a t r a n s p o s i t i o n a l e r r o r in wr i t ing or

typing the t e x t .

Table 9 summarizes information on t r s n s i t i o n zones. Both the zones

suggested in the Phase I1 r e p o r t and zones suggested by r e l a t i v e dens i ty

e s t i m a t e s from benth ic core o t t e r t r awl sampling (Table 7 ) a r e included.

T r a n s i t i o n zones def ined by the d i f f e r e n t c r i t e r i a do not exac t ly

correspond. In p a r t i c u l a r , t he t r a n s i t i o n zones defined in the r e p o r t ,

which may be based p r imar i ly on s p e c i e s d i s t r i b u t i o n s and spec ies d i v e r s i t y

and inc lude cons ide ra t ion o f q u a l i t a t i v e da ta from dredges and o the r

sampling in a d d i t i o n to benth ic core d a t a , d i f f e r from the t r a n s i t i o n zones

suggested by the benth ic core da ta alone. In p a r t i c u l a r , they d i f f e r fo r

anne l ids . Annelid d e n s i t i e s were r e l a t i v e l y h igh a t s t a t i o n T-40, y e t t h i s

was i n d i c a t e d as a t r a n s i t i o n zone f o r anne l ids in the Phase I r e p o r t .

Annelid d e n s i t i e s were lowest a t T-7, T-19, and T-27. Mollusc d e n s i t i e s

a l s o were extremely low a t these t h r e e s t a t i o n s compared to elsewhere.

Crustacean d e n s i t i e s were lowest a t s t a t i o n s T-7 and T-19 and increased

Table 9 . T r a n s i t i o n zones of t h e r i v e r s u g g e s t e d by i n d i c a t e d c r i t e r i a .

* _ .. T r a n s i t i o n Zone

C r i t e r i a L i m i t s by T S t a t i o n L i m i t s by River Mile

Taxonomic D i s t r i b u t i o n s

Anne l ids 7 4 0 7 5

Mol luscs

Crustaceans

F i s h l a r v a e

R e l a t i v e D e n s i t y

F i s h

Hogchoker

Benthos

Mol luscs

Crustaceans

Annel ids

9 - 4 4 2 . 5 - 1 6 . 5 3 9 - 25 ( h i g h l y

s t r e s s e d )

from T-27 through T-53. Based on b e n t h i c d e n s i t i e s , t he r i v e r can be

s e p a r a t e d i n t o a low d e n s i t y and s high d e n s i t y zone, t h e h igh d e n s i t y zone

-oovering Upper C h a r l o t t e Harbor w d some por t ion of Myakks Bay and tlfe low

d e n s i t y zone inc lud ing the b ra ided r i v e r a r e a end eve ry th ing upstream.

Data presented in t h e two r e p o r t s s t r o n g l y sugges t t h a t s a l i n i t y

i n f l u e n c e s bo th t h e number and d e n s i t y o f b e n t h i c s p e c i e s in var ious

segments of t h e Hyakks R ive r , bu t it is n o t c l e a r whet a s p e c t of s a l i n i t y

i s determining the presence o r absence o f s p e c i e s and t h e i r dens i ty . In

t h e Phase I1 r e p o r t i t was suggested t h a t the t r a n s i t i o n zones

d i s t i n g u i s h e d by b e n t h i c s p e c i e s d i s t r i b u t i o n s may be the a r e a of g r e a t e s t

s a l i n i t y f l u c t u a t i o n s . Tab le 10 summarizes information on a r e a s of

g r e a t e s t s a l i n i t y f l u c t u a t i o n s between t i d e s a t t h e t h r e e times of s a l i n i t y

measurement: mid dry season (Apr i l 14-15, 1987) and wet season (September

10 and 24 , 1985). During both wet and dry season sampling, between-tide

s a l i n i t y f l u c t u a t i o n s were g r e a t e r st s t a t i o n T-40 (lower Myakks Bay) than

anywhere e l s e t h a t ben th ic c o r e sampling was conducted; y e t t h i s s t a t i o n

had b e n t h i c d e n s i t i e s second only t o t h a t st T-53 and the h ighes t d e n s i t i e s

of f i s h . Th i s sugges t s t h a t t h e a r e a s o f lowest ben th ic d e n s i t i e s do no t

correspond t o t h e a r e a s o f g r e a t e s t between-tide s a l i n i t y f l u c t u a t i o n s .

According to Remane and S c h l i e p e r (1971), t h e lowest number of s p e c i e s

on a s a l i n i t y g r a d i e n t o f t e n is found somewhere between 1 and 5 pp t .

Boesch (1977) found t h a t b e n t h i c d e n s i t i e s in Chesapeake Bay were lowest in

t h e r eg ion o f Chesapeake Bay exper i enc ing s a l i n i t i e s of about 1 t o 5 ppt .

The Myakka River zone of low d e n s i t y appea r s t o extend f u r t h e r up r ive r than

t h e a r e s t h a t exper i ences s a l i n i t i e s between 1 and 5 pp t wst o f t e n .

Perhaps t h e zone o s low d e n s i t y b e s t corresponds t o t h e s t r e t c h o f t h e

r i v e r t h a t f r e q u e n t l y exper iences s a l i n i t i e s of l e s s than 1 pp t and occs-

a i o n a l l y exper i ences a a l i n i t i e g o f g r e a t e r than 1 (o r 5 1 ) ppt. T h i s f i t s

t h e d e s c r i p t i o n o f t h e mid-river zone o f t h e second zonat ion scheme

-descr ibed above and presented in the Phaae I and Phase I1 r e p o r t . .

Another p o s s i b i l i t y is t h a t the zone of low ben th ic d e n s i t i e s

correaponda t o the aegment o f t h e r i v e r t h a t exper i ences t h e g r e a t e s t

v a r i a t i o n in s a l i n i t i e s between seaaons. Benthic s p e c i e s may be a b l e t o

adapt b e t t e r t o f r equen t short-term changea in s a l i n i t y than to longer-term

changea in s a l i n i t y t h a t occur seasona l ly . F u r t h e r examination of da ta in

t h e Phaae I and Phase I1 r e p o r t s and new d a t a c o l l e c t e d in m r e r e c e n t l y

monthly surveys could p a a l b l y p inpo in t t h e a s p e c t o f s a l i n i t y v a r i a t i o n in

t h e r i v e r t h a t bea t d e s c r i b e s the v a r i a t i o n in ben th ic s p e c i e s d i s t r i b u -

t i o n s and d e n s i t i e s .

5 . S p a t i a l and Temporal V a r i a t i o n and Management Changes

The primary o b j e c t i v e s o f t h e Phaae I and Phaae I1 s t u d i e s were t o

de termine b a s e l i n e c o n d i t i o n s in t h e r i v e r wi th which to e v a l u a t e p o s s i b l e

e f f e c t a o f water management a c t i o n s and land use changes on t h e produc-

t i v i t y o f t h e r i v e r . Water management a c t i o n a t h a t have been proposed

i n c l u d e (1) a propoaed p r o j e c t to use t h e Ringl ing HcArthur P rese rve to

t r e a t and r e c y c l e secondary sewage wa te r s , which could a f f e c t the n u t r i e n t

l o a d o f t h e r i v e r ; ( 2 ) a proposed p r o j e c t t o d i v e r t up t o 5% of t h e flow of

t h e Myakka River f o r upstream uaea , which might a l t e r the s a l i n i t y s t ruc -

t u r e o f t h e r i v e r ; and ( 3 ) a proposed p r o j e c t to p lug the (Xlrry Canal,

which a l s o could a f f e c t the s a l i n i t y s t r u c t u r e o f the r i v e r . Changea in

l a n d use , such a s conversion from p a s t u r e t o c i t r u s , o r changea in on-s i te

water management p r a c t i c e s could a f f e c t the r i v e r by a f f e c t f n g s a l i n i t y

Table 10. Stretches of the river experiencing greatest change in salinity of bottom waters, by date, as interpolated from graphs in Phase I and Phase I1 reports.

Change in

Salinity ID

Date

Apr 14,15,'86 Sep 10,'85 Sep 24,'85

River Mile -2 - 13.1 -2 - 6.2 0.7 - 7.1 < 2 T-Station 53 - 18 53 - 38 50 - 36

Description mouth - near mouth - UMB MH - near UMB m

River Mile 5.2 - 10.8 0.5 - 5.2 1.8 - 4.3,S.g 2 > 5 T-Station 40 - 26 50 - 40 46 - 41,38

Description IMB - M - IMB Tippecanoe IMB,UMB Bay

River Mile 5 > 8 T-Station

Description

- - - --

Salinity Change

Distance of Indicated Salinity Change (miles)

Apr 14,15,'86 Sep 10,*85 Sep 24,'85

Note: River mile measurement starts at Cattle Dock Point. -2 is two miles downstream from Cattle Dock Point. 5 is five miles upstram from Cattle Dock Point.

Mean discharge rates: March, 1986 = 137.3 cfs April, 1986 = 43.5 cfs Sept, 1985 = 656.0 cfs

s t r u c t u r e o r n u t r i e n t concentrht ions. The Phase I and Phase I1 r e p o r t s

he lp us t o understand the dimensions o f v a r i a t i o n in these important - . v a r i a b l e s and t h e i r r ami f i ca t ions .

Freshwater Inf low E f f e c t s

The r e l a t i o n s h i p o f freshwater inf low t o e s t u a r i n e p roduc t iv i ty is

complicated by many dimensions of v a r i a b i l i t y in causa l and responding

agents . Furthermore, t he impact of changes is d i f f i c u l t t o eva lua te

because impacts occur a t s e v e r a l l e v e l s . Freshwater flow in f luences s a l i -

n i t i e s , n u t r i e n t concen t ra t ions , and exchange with oceanic waters; and i t

i s probably through these f a c t o r s t h a t changes in the flow of f r e s h water

a f f e c t e s t u a r i n e p roduc t iv i ty and nur se ry value. Determining the impact of

a l t e r i n g f reshwater flow is d i f f i c u l t due to t h e complicat ions t h a t impede

es t ab l i shment of t h e fundamental r e l a t i o n s h i p s .

V a r i a b i l i t y i s due to many f a c t o r s . S a l i n i t y v a r i e s with d i s t ance

from the r i v e r mouth; then , a t every l o c a t i o n within the r i v e r , s a l i n i t y

v a r i e s cont inuously with the t i d e a s w e l l a s by season and ac ross years.

Furthermore, s a l i n i t i e s in C h a r l o t t e Harbor, which a r e a f f e c t e d by the flow

o f t h e Peace River , a f f e c t s a l i n i t i e s in t h e Myakka River , a t l e a s t

downstream.

Mixing wi th in the r i v e r is s t rong ly inf luenced by freshwater flow, but

t h e r e l a t i o n s h i p is nonl inear . Inc reases in freshwater flow enhance mixing

up t o a po in t , beyond which v e r t i c a l mixing is i n h i b i t e d and s t r a t i f i c a t i o n

occurs . The po in t a t which freshwater flow causes s t r a t i f i c a t i o n d i f f e r s

n o t on ly by e s t u a r y but a l s o due to temperature, wind e f f e c t s , mad o t h e r

f a c t o r s . When s t r a t i f i c a t i o n occurs , s a l i n i t y v a r i e s wi th depth, and bot-

tom i s o h a l i n e s a r e pos i t ioned d i f f e r e n t l y in the r i v e r than su r face iaoha-

l i n e s .

S a l i n i t y in e s t u a r i e s and t i d a l r i v e r s is d i r e c t l y r e l a t e d t o fresti-

.. .' . water flow and i ts v a r i a t i o n over space and time has an in f luence on the

s u r v i v a l and growth of e s t u a r i n e organisms, but t h e exact mechanisms f o r

t h i s in f luence a r e not known and m y even d i f f e r by species . The physiolo-

g i c a l and eco log ica l requirements regarding s a l i n i t y d i f f e r by spec ies .

Within a s p e c i e s , t hese requirements even d i f f e r by s i z e o r age group. The

s u r v i v a l and growth of a c e r t a i n spec ies end age group a t various s a l i n i -

ties no t only depends upon the phys io log ica l requirements of t h a t organism

but a l s o upon t h e phys io log ica l requirements o f i ts p reda to r s , i ts prey,

and the food of i ts prey. For t h i s reason, i n d i c a t o r s of su rv iva l and

growth o f even one s p e c i e s r e f l e c t t h e i n t e g r a t i o n of m u l t i p l i c a t i v e

i n t e r a c t i o n s with the environment. Furthermore, v a r i a t i o n in t roph ic

s t r u c t u r e between ecosystems may cause d i f f e r i n g responses of the same spe-

c i e s t o s a l i n i t y in two d i f f e r e n t systems.

An environmental change can cause a s h i f t i n dominance from one group

o f s p e c i e s t o another and y e t cause l i t t l e change a t the ecosystem leve l .

I f t h e e x t a n t dominants have a recognized value to human s o c i e t y and t h e i r

replacements do n o t , then s o c i e t y r e a l i z e s a b a a from the change, d e s p i t e

t h e l a & of major impact on the ecosystem. On t he o t h e r hand, when environ-

mental change r e s u l t s in s l o s s o f p r o d u c t i v i t y , a reduct ion in energy

flow, and a reduct ion in biomass, t h e e f f e c t s of the environmental change

are f e l t a t t he ecosystem leve l . These e c o s y s t e w l e v e l changes mean con-

vers ion from a h ighly product ive system to a r e l a t i v e l y barren one.

Because o f d i f f e r e n c e s In t r o p h i c s t r u c t u r e among ecosystems, d i f -

f e r e n c e s in t h e i r dominant s p e c i e s and t h e i r s p e c i e s pools , these

ecosystems' p o t e n t i a l responses t o changed condit ions-their a b i l i t i e s to . adapt-may d i f f e r .

_ .. We u l t i m a t e l y must be concerned with how the ecosystem is a f f e c t e d by

a l t e r a t i o n s . But primary responses a r e made a t t he l e v e l of spec ies , w i th

d i f f e r e n t responses occur r ing a t d i f f e r e n t developmental s tages . For t h i s

reason, we c e r t a i n l y have to determine e f f e c t s a t the l e v e l o f spec ies and

age groups wi th in species . In doing t h i s , we should w n c e n t r a t e on the

s p e c i e s t h a t p r e s e n t l y a r e dominant in t h e system, f o r t h e i r abundance

r e l a t i v e t o o t h e r spec ies sugges t s t h a t t h e i r metabolism rep resen t s major

f lows o f energy through the system. We should n o t , however, ignore the

p o s s i b i l i t y o f measuring ecosystem-level parameters t h a t might d i f f e r l ~ >

r e l a t i o n to sa l in i ty -ben th ic metabolism, f o r ins tance .

What a s p e c t s of s a l i n i t y c o n t r o l the s u r v i v a l and growth of organisms

i n the t i d a l r i v e r m d es tua ry? In a paper with Don & o r e (Browder and

Moore 19811, I proposed t h a t s u r v i v a l and growth in e s t u a r i e s is a funct ion

o f t h e a r e a of ove r l ap o f c e r t a i n s t r u c t u r a l f e a t u r e s of the h a b i t a t t h a t

a r e important to a s p e c i e s ( i .e . bottom depth, s h o r e l i n e l eng th , o r vegeta-

t i o n cover) wi th water wi th in a c e r t a i n s a l i n i t y range t h a t i s somehow

favorab le t o t h a t species . The concept was founded on the range management

concept t h a t h a b i t a t d i f f e r s in q u a l i t y and acreage o f h a b i t a t , by q u a l i t y

type , l i m i t s production. In a s tudy in Faka &ion Bay, John Wang and I

(Browder and Wang 1987) showed t h a t v a r i a t i o n in t he r e l a t i v e abundance of

s e v e r a l s p e c i e s of f i s h and macroinver tebra tes over time was s i g n i f i c a n t l y

r e l a t e d to a r e a o f t h e bay wi th in c e r t a i n s a l i n i t y bands. S t u d i e s by

Hansen (1969), Herke (1971) ard o t h e r s , a s we l l a s information presented in

t h e Phase I and Phase I1 r e p o r t s , suggest t h a t both the h a b i t a t f e a t u r e s

and the s a l i n i t y ranges f avorab le to a spec ies may d i f f e r according to s i z e

o r l i f e s tage.

Other a s p e c t s of sa l in i ty-may a l s o s t rong ly in f luence organismic sur-

v i v a l and growth. For some spec ies , minimum s a l i n i t i e s o r the dura t ion and - . frequency o f lower s a l i n i t i e s may be governing. For o t h e r spec ies , maximum

s a l i n i t i e s may be l imi t ing . Dif ferences in s u r v i v a l and growth a r e

r e f l e c t e d a s d i f f e r e n c e s in abundance and biomass.

T i d a l r i v e r and e s t u a r i n e organisms can be divided in to four groups

that, because o f b a s i c d i f f e r e n c e s in t h e i r behavior and h a b i t a t , can be

expected to be inf luenced d i f f e r e n t l y by s a l i n i t y v a r i a t i o n w d to r e f l e c t

t h i s in f luence d i f f e r e n t l y in t h e i r abundance and biomass. These a r e

b e n t h i c s e s s i l e organ isms, ben th ic m t i l e organisms, demersal feeding

m o t i l e organismu, and pe lag ic species . S a l i n i t y - r e l a t e d d i f f e r e n c e s in

abundance in t he f i r s t group a r e r e l a t i v e l y easy t o d e t e c t . The responses

o f t h e second and t h i r d group a r e m c h nore complex and our a b i l i t y t o

d e t e c t t h e i r responses much more d i f f i c u l t . It is d i f f i c u l t t o d i s t i n g u i s h

between t r u e abundance and mere changes in r e l a t i v e dens i ty a s animals m v e

around. It can be done, h w e v e r , by sampling by type of h a b i t a t , knowing the a r e a

o f each h a b i t a t type, and sampling i n t e n s i v e l y in space and time.

The e n t r y of new young organisms i n t o the system mmpl ica te s the w a -

l y s i s o f v a r i a t i o n in abundance in r e l a t i o n to environmental va r i ab les . It

is impera t ive t o understand the seasonal cyc le of reproduction and r e c r u i t -

ment in o r d e r to eva lua te temporal changes i n abundance. Immigration of

o l d e r organisms t o h ighe r - sa l in i ty environments is another f a c t o r t h a t

compl ica tes t h e i n t e r p r e t a t i o n o f change in abundance over time.

The Phase I and Phase I1 r e p o r t s have provided e s p e c i a l l y l u c i d two-

dimensional deac rp t ions of how s a l i n i t y v a r i e s in the Myakka River. The

view of t i d a l excurs ions in which i e o h a l i n e s a r e shorn moving up and

down the r i v e r with each t i d a l ' c y c l e is a p a r t i c u l a r l y i n t e r e s t i n g one t h a t

1 have never previous ly encountered. I th ink t h a t a s tudy from t h i s -. . ) *

viewpoint promises to y i e l d m r e u s e f u l information on the d i s t r i b u t i o n of

macroinver tebra tes and f i s h in r e l a t i o n t o s a l i n i t y than any antecedent . I

have found the Phase I and Phase I1 r e p o r t s very e x c i t i n g to review f o r

t h i s reason. These r e p o r t s w d the extens ion of these s t u d i e s w i l l pave

t h e way f o r determining s p e c i f i c r e l a t i o n s h i p s between s a l i n i t y and the

d i s t r i b u t i o n and abundance of organisms, which should f a c i l i t a t e r e l i a b l e

p r e d i c t i o n s o f p o t e n t i a l impacts on n a t u r a l resources of a l t e r e d land uses,

l o c a l water management p r a c t i c e s , and la rge-sca le management ac t ions .

Phys ica l m n d i t i o n s such a s turbulence , bottom scouring, and the cir-

c u l a t i o n and mixing of water masses a l s o vary with freshwater flow and may

a f f e c t the s u r v i v a l and gfrwoth of f i s h and benth ic organisms. We need to

gain more i n s i g h t on these phys ica l conditions-how they vary with fresh-

water flow, how they d i f f e r in var ious segments of the r i v e r , and h o w they

a f f e c t var ious organisms. L i t t l e information on these a spec t s of r i v e r

in f luence were covered in the Phase I and Phase I1 r e p o r t s .

Nu t r i en t Concent ra t ions

Although the tm s t u d i e s placed l e s s emphasis on n u t r i e n t dynamics and

t h e v a r i a t i o n in n i t rogen concen t ra t ions in time and space than they d id on

s a l i n i t y v a r i a t i o n s , they d id i d e n t i f y s e v e r a l a s p e c t s of r i v e r ecology

that may have g r e a t bear ing on how t h e r i v e r might respond t o increased

n u t r i e n t s from a wastewater r ecyc l ing f a c i l i t y , p a s t u r e s , o r a g r i c u l t u r a l

f i e l d s . F i r s t , n i t r o g e n , a s opposed to phosphorus, is t h e l i m i t i n g f a c t o r

t o primary p r o d u c t i v i t y in the Myakka River. Second, d isso lved oxygen

l e v e l s in bottom waters sometimes f s l l below F l o r i d a water q u a l i t y etan-

da rds , poss ib ly suppress ing benth ic secondary product iv i ty . Levels below 4

mg/l wmmonly occur upr ive r (near Snook Haven), and, under s t r a t i f i e d - wn- -. d i t i o n s , a l s o a r e found downriver ( i n Zones 3 and 4 ) . Third , t he area of

emergent vegetat ion in the Myakka River r e l a t i v e to the su r face area of the

r i v e r is extremely l imi t ed . Four th , submerged vegeta t ion in upstream por-

t i o n s o f the b a k k a River may be l igh t - l imi t ed due to color in the water.

The water is c l e a r e r downstream, poss ib ly because of the f l o c c u l a t i o n w d

p r e c i p i t a t i o n o f co lo r compounds when freshwater mixes with s a l t water

( t h e Phase I and Phase I1 r e p o r t s suggest t h a t , in the Myakka River, t h i s

o c c u r s a t a s a l i n i t y of about 6 ppt ) . Simple d i l u t i o n of r i v e r water with

clearer waters from C h a r l o t t e Harbor may a l s o improve water c l a r i t y . The

Phase I and Phase 11 r e p o r t s suggest t h a t ex tens ive seagrass beds occur in

downriver po r t ions of the Myakka; but t h a t they a r e found only in shallower

a r e a s , i n d i c a t i n g t h a t these beds may be e x i s t i n g a t minimum l i g h t l e v e l s

now.

Here we have s e v e r a l elements of concern: Nitrogen inpu t s can be

expected to inc rease primary p roduc t iv i ty . The p t e n t i a l fo r emergent

vege ta t ion to t ake up n i t rogen may be extremely l imi ted . Submergent vege-

t a t i o n in the upper r i v e r probably w i l l no t be a b l e to absorb a d d i t i o n a l

n u t r i e n t s . Of a l l the primary producers , phytoplankton in the lower r i v e r

may have t h e g r e a t e s t p o t e n t i a l to inc rease in response to increased n i t ro -

gen. I f t h i s occurs , l i g h t t ransmission to the grassbeds in the lower

r i v e r w u l d be reduced, causing a loss of these beds. To the ex ten t t h a t

n u t r i e n t concen t ra t ions a r e above ambient a t t he mouth o f t h e Myakka River ,

grassbeds in Char lo t t e Harbor could a l s o be a f f e c t e d . An ecosystem m d e l

o f Chesapeake Bay by Kemp e t a l . (1983) suggested t h a t the s t imula t ion of

phytoplankton p roduc t iv i ty by added n u t r i e n t s was t h e leading cause of t h e

l o s s o f seagrass beds t h e r e and t h a t the s e a g r s s s l o s s e s could be

s e s p o n s i b l e f o r observed d e c l i n e s in s todcs of f i s h , c rabs , and o y s t e r s in

Chesapeake Bay.

I f water-column primary p roduc t iv i ty inc reaaes and bottom vegetat ion

dec reases , ben th ic biomass, secondary p r o d u c t i v i t y , and the value of the

r iver -es tuary a s a nu r se ry ground f o r f i s h and inverLebrate spec ies is

l l k e l y t o diminish f o r s e v e r a l reasons. F i r s t , bottom vegetat ion is an

important h a b i t a t f o r t h e young of many s p e c i e s of f i s h and shrimp, who a r e

found in higher concen t ra t ions in these beds than elsewhere. Surviva l of

t h e s e organisms m u l d l i k e l y be a f f e c t e d f o r t h i s reason alone i f seagrass

a r e a decreased. But perhaps of even g r e a t e r concern, increased phytoplank-

ton production would add to the b i o l o g i c a l oxygen demand of bottom waters

st the same time the production of oxygen in bottom waters by seagrasses

was depressed. The poss ib le importance o f seagrasses in con t r ibu t ing

d i s so lved oxygen to bottom waters through photosynthes is should not be

overlooked. Although the a r e a o f coverage by submerged aqua t i c vegeta t ion

in the upper r i v e r may be smal l , t h i s , t oo , may be playing an important

r o l e i n supplying oxygen to bottom waters. Both ben th ic organisms and

demersal f i s h a r e d e t r i m e n t a l l y a f f e c t e d by low M). Although f i s h can move

t o o t h e r a r e a s to avoid an oxygen dep le t ion event , moving may a f f e c t t h e i r

s u r v i v a l p o t e n t i a l by inc reas ing f i s h d e n s i t i e s and the i n t e n s i t y of tor

p e t i t i o n in s u b s t i t u t e l i v i n g w d feeding a reas . Furthermore, ben th ic

organisms, many of which do no t move, can be k i l l e d by low oxygen events.

T h i s can depress ben th ic secondary p r o d u c t i v i t y , which equates d i r e c t l y

wi th food a v a i l a b i l i t y t o demersal-feeding f i s h . According t o the Phase I

and Phase I1 r e p o r t s and my t r o p h i c a n a l y s i s , t h i s inc ludes a l l t he major

s p e c i e s o f f i s h in the Myakka River.

An inc rease in n u t r i e n t s in t h e watershed may no t only inc rease n i t r o - - .' . gen i n p u t s t o the r i v e r but a l s o the load of o rgan ic matter the r i v e r

r e c e i v e s from the vatershed. Land spreading of waste water , t h e wastes o f

domestic animals , and commercial f e r t i l i z e r s s t imula te primary production

in the watershed, r e s u l t i n g in an inc rease in o rgan ic matter in runoff .

I n p u t s of o rgan ic matter have a d i r e c t e f f e c t on BOD. Th i s i s of par-

t i c u l a r concern in the upper r i v e r , where DO l e v e l s a l r eady a r e o f t e n below

s t a t e s tandards . Belanger (1985) has noted t h s t low W l e v e l s a r e a chro-

n i c condi t ion of h ighly colored waters of F lo r ida . Because M) l e v e l s in

t h e s e waters a r ? n a t u r a l l y low, they may be extremely vulnerable to

increased inpu t s of o rgan ic matter.

References

Belanger, T.V., F.E. Dierberg,'and J. Roberts. 1985. Dissolved oxygen wn- c e n t r a t i o n s in F l o r i d a ' s humic-colored waters and water q u a l i t y s tandard impl i ca t ions . F l o r i d a S c i e n t i s t 48: 107-119.

I .' - Boesch, D.F. 1977. A new look a t t h e zonation of benthos along the e s t u a r i n e

g rad ien t . p 245-266 in: B.C. B u l l (ed.). Ecology of Marine Benthos. Univ. South Carol ina Press. Columbia, S.C. 467 p.

Browder, J.A., and D. Moore. 1981. A new approach to determining the quanti- t a t i v e r e l a t i o n s h i p between f i s h e r y production m d the flow of f r e s h water t o e s t u a r i e s . p 403-430 in : R. Cross and D. Williams (eds.). Proc. Nat ional Symp. on Freshwater Inflow t o Es tua r i e s . Vol. 1. U.S. F i sh and W i l d l i f e Service , Of f i ce of B io log ica l Services . FWS/OBS-81/04.

Browder, J.A., and J.D. Mng. 1987. Modeling water management e f f e c t s on marine resource abundances in Faka Union Bay, F lo r ida . in: Proc. Symp. on t h e ecology and mnse rva t ion of wetlands of the Usumacinta and G r i j a l v a d e l t a , Vil laherrmsa, Tabasco, Mexico, February 2-6, 1987. 21 p.

Carr W.E.S., and C.A. Adams. 1973. Food h a b i t s of juven i l e marine f i s h e s occupying seagrass beds in the e s t u a r i n e zone near Crys ta l River , F lo r ida . Trans. Am. Fish. Sac. 102: 511-540.

Colby, D.R., G.W. Thayer. W.F. Hettler. and D.S. Pe te r s . 1985. A comparison of fo rage f i s h communities in r e l a t i o n t o h a i t a t parameters in Faka Union Bay, F l o r i d a , and e i g h t m l l a t e r a l bays dur ing the wet season. NOAA Tech. Mem. NMFS-SEFC-162. National Marine F i s h e r i e s Se rv ice , Southeast F i s h e r i e s Center. Beaufort , N.C. 28516. 87 p.

D a r n e l l , R.H. 1958. Food h a b i t s of f i s h e s and l a r g e r i n v e r t e b r a t e s of M e P o n t c h a r t r s i n , Louisiana, an e s t u a r i n e community. Publ. Ins t . Mar. Sci . Tex. 5: 353-416.

Hsnsen, D.J. 1969. Food, growth, migra t ion , reproduct ion , and abundance of p i n f i s h , Lagodon r h m b o i d e s , and A t l a n t i c c roaker , Micropogon undulatus, n e a r Pensacola, F l o r i d a , 1963-1965. Fish. Bull. 68: 135-146.

Nichols , F.H. 1977. Infaunal biomass and production on a mudflat , San Francisco Bay, Ca l i fo rn ia . p 339-357 in: B.C. Coull (ed.). Ecology of Marine Benthos. Univ. South Carol ina P ress , Columbia, S.C. 467 p.

Odum. W.E.. and E. J. Heald. 1972. Trophic analyses o f an e s t u a r i n e mangrove community. Bull. Mar. Sci. 22: 671-738.

Reid, G.K., Jr. 1954. An e c o l o g i c a l s tudy of the Gulf of Mexico f i s h e s , in the v i c i n i t y of Cedar Key, F lo r ida . Bull. Mar. Sci. Gulf. and Caribb. 1: 1-94.

Remane, A., and C. Schl ieper . 1971. Biology of Brackish Water. Wiley, New York. 372 p.

Virnstein, R.W. 1977. The importance of predat ion by c rabs and f i s h e s on b e n t h i c infauna i n Chesapeake Bay. Ecology 58: 1199-1217.

REVIEW OF DRAFT REPORT ON EVALUATION OF WATER QUALITY IMPACTS

Uy comments concern p r imar i ly the m n t h l y regress ion equat ions y e d -. f o r p r e d i c t i o n of s a l i n i t i e s and s a l i n i t y change with flow reduct ion a t

Snook Haven, Por t Char lo t t e , and E l Jobean.

I ques t ion whether Peace River d i scha rge r a t e s s k u l d have been l e f t

o u t o f these f i n a l equat ions. Peace River d ischarge mst have a s t rong

a f f e c t on s a l i n i t i e s in Char lo t t e Earbor, and Char lo t t e Harbor waters a r e

t h e wa te r s t h a t mix with l o c a l f reshwater inf low t o determine Myakka River

s a l i n i t i e s . Unfortunately, t h e m u l t i p l e c o r r e l a t i o n c o e f f i c i e n t s were not

included with the f i n a l p r e d i c t o r equat ions , so I can not use t h i s to WE-

p a r e them wi th the o r i g i n a l equat ions , f o r which m l t f p l e c o r r e l a t i o n w e f -

f i c i e n t s were included. Mul t ip l e c o r r e l a t i o n c o e f f i c i e n t s f o r the f i n a l

p r e d i c t o r equat ions should be included in the f i n a l r epor t .

Can I assume t h a t the s a l i n i t i e s used t o develop the equat ions were

"high t i d e " e a l i n i t i e s ? T h i s was n o t ind ica ted in the r e p o r t , however t i d e

s t a g e s used in the equat ions were high t i d e s tages .

The t i d e s t a g e da ta were f o r S t . Petersburg. The t a b l e on

d e s c r i p t i o n of da ta s e t s ind ica ted t h a t the St. Petereburg data extended

i n t o 1985. Are these da ta s t i l l being c o l l e c t e d ? I f n o t , it is n o t very

u s e f u l to f u t u r e work to have equat ions t h a t a r e dependent upon them.

Can mmparable long term data on t i d a l s t a g e be c o l l e c t e d in Char lo t t e

Barbor o r , perhaps p re fe rab ly , t h e ocean o u t s i d e Char lo t t e Harbor in the

f u t u r e ?

Two a s p e c t s of the p r e d i c t i v e equat ions suggest t h a t v a r i a b l e s not

inc luded in the equat ions may s t r o n g l y a f f e c t s a l i n i t y in the Myakka River.

F i r s t , t h e r eg ress ion c o e f f i c i e n t s d i f f e r e d cons iderably among m n t h s .

Secondly, t h e m u l t i p l e c o r r e l a t i o n c o e f f i c i e n t s f o r the o r i g i n a l equat ions

were below 0.7 (equivalent to 49% of var iance in the dependent v a r i a b l e

expla ined by t h e equation) f o r a l l m o t h s except June. August. September. - .' and October. I sugges t Chat, in add i t ion to inc luding Peace River

d i scha rge in the f i n a l equat ions , some e f f o r t be made t o f i n d the o the r

c o n t r o l l i n g va r i ab les . I b e l i e v e vind speed is the m a t l i k e l y . 'I suggest

t h e equat ions be rerun us ing the fol lowing four var iables : Wind speed

nor the rn s e c t o r , wind speed southern s e c t o r , wind speed eas t e rn s e c t o r , and

wind speed western sec to r . I f t h i s g ives a poor f i t . I suggest you t r y

wind speed northwestern s e c t o r , wind speed nor theas te rn s e c t o r , wind speed

southwestern s e c t o r , wind speed southeas tern crector. There is a good

chance t h a t one o r a combination of these w i l l improve the p red ic t ion capa-

b i l i t y .

Another poss ib le reason f o r low mul t ip l e c o r r e l a t i o n c o e f f i c i e n t s and

poor correspondence of r eg ress ion c o e f f i c i e n t s among months is that s a l i -

n i t y may n o t be l i n e a r l y r e l a t e d to freshwater inflow. A s a matter of

f a c t , Wang and Browder (1986) found an i nve r se hyperbolic r e l a t i o n s h i p bet-

ween s a l i n i t y and freshwater inf low in Faka Union Bay, Flor ida .

The equat ions probably could be improved considerably i f a d d i t i o n a l

d a t a on s a l i n i t y were c o l l e c t e d and i f s t a g e da ta were c o l l e c t e d a t t he

t h r e e s t a t i o n s a t t he time of each s a l i n i t y c o l l e c t i o n . Data should be

c o l l e c t e d a t high s t a g e , low s t a g e , and mid stage.

I n add i t ion t o improving these equat ions , t he fol lowing needs should

be addressed in f u t u r e w r k :

* 1. Pred ic t ion of l o r t i d e s a l i n i t i e s a t the t h r e e s t a t i o n s .

2. P red ic t ion of the s p a t i a l d i s t r i b u t i o n of high t i d e and low t i d e

s a l i n i t i e s between the t h r e e s t a t i o n s .

3. R e d i c t i o n of between-tide s a l i n i t i e s a t t he t h r e e s t a t i o n s and

l o c a t i o n s in between. . - .' Although the equat ions can probably be improved v l t h no a d d i t i o n a l

d a t a w l l e c t i o n , I s t r o n g l y recommend t h a t a d d i t i o n a l da ta be c o l l e c t e d and

t h a t d a t a to p r e d i c t low t i d e ss l ini t ies , between-tide s a l i n i t i e s , aud

s a l i n i t i e s between s t a t i o n s a l s o be co l l ec ted .

REVIEW (IF ECOSYSTEM MODELS ON ESTUARINE MANACEMEW PROBLEMS

A review of ecosystem m d e l s appl ied to management ques t ions in o t h e r - ,. . e s t u a r i e s , p a r t i c u l a r l y in F l o r i d a , may provide i n s i g h t to a i d in planning

a s tudy t o eva lua te p o t e n t i a l impscts of management op t ions concerning the

Myakka River. I am going to w n f i n e my d iscuss ion to m d e l s t h a t have

a c t u a l l y been q u a n t i f i e d and executed. To my knowledge, t h e r e a r e only two

such models-that by Boynton ( 1 9 7 7 ) f o r the Apalachicola e s tua ry and t h a t

by Kemp (1977 and 1980) f o r C r y s t a l River. I am a l s o going to d iscuss

t h r e e e s t u a r i n e ecosystem w d e l s f o r a r e a s o u t s i d e of F l o r i d a t h a t seem

r e l e v a n t t o the problems of concern in the Myakka River.

Modeling WKS p a r t of a r eg iona l s tudy to eva lua te t h e p o t e n t i a l e f f e c t

of a proposed dam on the Apalachicola River on the o y s t e r beds of

Apalachicola Bay and t h e p o s s i b l e consequences f o r Lhe economy of Frankl in

County. (h t h e b a s i s of 24 hour measurements of d isso lved oxygen (DO),

Boynton es t imated primary p roduc t iv i ty (daytime change in DO) and r e s p i r s -

t i o n (n ight t ime change in DO) in f i v e types of h a b i t a t s . He found t h a t the

P/R raLio was g r e a t e r than 1 over grassbeds and in a medium s a l i n i t y plank-

ton system ( t h e type of system occur r ing over o y s t e r beds). The P/R was

less than 1 i n boat bas ins and in an o l i g o h a l i n e system. Highest r a t e s of

photosynthet ic a c t i v i t y were over grassbeds. H i s model of the medium s a l i -

n i t y plankton system suggested t h a t photosynthes is by phytoplankton was a

more important source of oxygen to the water w l u w than e i t h e r advection

or reae ra t ion . Never the less , i f r e a e r a t i o n were surpressed , mimicking

decreased turbulence o r s t r a t i f i c a t i o n , then e a r l y m r n i n g DO con-

c e n t r a t i o n s f e l l to about 3 ppm, approaching the l e v e l where w b i l e spec ies

might leave the a rea end many sessile benth ic organisms might be s t r e s sed .

The oxygen mmpsrtment was e l iminated in f u t u r e work with the model,

i n which he wupled it to a m d e l of t h e o y s t e r subsystem. The o y s t e r

a b d e l was n o t descr ibed in the t e x t , but Fig . 1 from Boynton i n d i c a t ; ~

t h a t i t has t h r e e compartments-juvenile o y s t e r s , a d u l t s , and oys te r preda-

t o r s . F resh water e n t e r i n g the system is shown to have s negat ive impact

on j u v e n i l e o y s t e r s and p reda to r s and no d i r e c t e f f e c t on a d u l t s except

through the e f f e c t of r i v e r flow on the a v a i l a b i l i t y of d e t r i t u s to both

j u v e n i l e and a d u l t oys te r s . The main e f f e c t of the r i v e r on the wup led

p lankton-oys ter system is to ca r ry n i t rogen and d e t r i t u s , t o lower s a l i n i -

t i e s , and to s t i m u l a t e turbulance. Nitrogen has a p o s i t i v e e f f e c t on pr i -

mary p roduc t iv i ty by phytoplankton. D e t r i t u s has s p o s i t i v e e f f e c t on

growth of juven i l e and a d u l t oys te r s . S a l i n i t y , which is, of course,

i n v e r s e l y r e l a t e d to freshwater inflow, has s negat ive e f f e c t on juven i l e

o y s t e r s and o y s t e r predators . The n e t r e s u l t of these e f f e c t is apparent

i n s imula t ions t e s t i n g the e f f e c t on oya te r biomass of (1) reducing the

ampli tude of the seasonal pulse of water flow, ( 2 ) i nc reas ing the t o t a l

annual flow, and ( 3 ) decreas ing the to ta l annual flow. Adult o y s t e r

biomass increased with r i v e r flow p a t t e r n s having seasonal pulses of lower

ampli tude than the c o n t r o l pulse but the same amount of freshwater input .

S u b s t a n t i a l i nc reases o r decreases in the t o t a l annual freshwater input

produced smal ler than normal o y s t e r s tocks . Details of t h e oys te r m d e l

need to be examined m r e c l o s e l y in order t o eva lua te the model and i t s

impl i ca t ions .

Th i s m d e l is an i n t e r e s t i n g example of an extremely s impl i f i ed eco-

system model used to eva lua te p o t e n t i a l e f f e c t s of proposed man-induced

changes in f reshwater flow. It does no t make any at tempt t o compare oys te r

Fig. 1. Regional model of Frank1 i n County and Apalachicola Bay, F l o r i d a . !from Boynton 1977)

h a r v e s t s in yea r s of varying freshwater inflow. The i n t e r f a c i n g of r i v e r

f low with b i o l o g i c a l a c t i v i t y is highly s i m p l i s t i c , poss ib ly because it was

- n p t supported by a phys ica l w d e l r e l a t i n g s a l i n i t y , mixing, w d ni t rogen

concen t ra t ions t o r i v e r flow. I am no t s u r e b w accura te ly t h e r e l a -

t i o n s h i p of freshwater to o y s t e r p reda to r s and juven i l e o y s t e r s were

de f ined , s i n c e no d e t a i l s of q u a n t i f i c a t i o n of these r e l a t i o n s h i p s was

descr ibed . T h i s model w i l l be a u s e f u l r e fe rence in conducting a systems

s tudy of the Myakka Rlver , but i t should no t be w p i e d because the systems

a r e d i f f e r e n t and the ques t ions being addressed a r e d i f f e r e n t .

Kemp (1977 and 1980) conducted an ecosystem a n a l y s i s to evalua te the

e f f e c t of a power-plant cooling canal on the Crys ta l River es tuary . A

t r o p h i c a n a l y s i s was a component of the s tudy (Fig. 2). One f e a t u r e of h i s

a n a l y s i s was a technique fo r c o l l a p s i n g s food web i n t o seve ra l food

cha ins by p a r t i t i o n i n g flows according to t h e i r t roph ic d i s t ance (number of

l i n k s ) from the food chain base ( t h e primary producer o r d e t r i t u s ) (Fig.

3 ) . A number of taxa a r e e i t h e r wholly o r p a r t i a l l y mcorpora ted i n t o each

consumer compartment. Those taxa that feed a t s e v e r a l t roph ic l e v e l s o r

a r e supported by s e v e r a l primary eources a r e included in w r e than one con-

sumer compartment. T h i s technique allows him to e a s i l y express , in terms

o f energy embodied a t the primary production l e v e l , the energy coat o r

b e n e f i t of various management op t ions t h a t a f f e c t t he production and

biomass o f f i s h and s h e l l f i s h .

The s t r u c t u r e of the s imula t ion w d e l developed by Kemp (1977) f o r the

i n t a k e canal and d ischarge basin of the C r y s t a l River power p l a n t i s shown

in Fig. 4. He d i s t ingu i shed water column d e t r i t u s (POC) from bottom d e t r i -

t u s and separa ted macroinver tebra tes i n t o suspension feede r s and depos i t

f e e d e r s , feeding on POC and o rgan ic sediments respect ive ly . He a l s o

- - Figure 2. Food web of chrystal River ecosystem.(from Kemp 1977).

Figure 3 . Food cha ins der ived from C r y s t a l River food w e b (from K e m p 1977)

Figure 4. Diagram of ecosystem model of two systems linked by a power plant at Crystal River (Kemp 1977).

d i s t i n g u i s h e d nekton from bentbos. The nekton were vulnerable to ent ra in-

ment in t h e power p l a n t condenser and the benthos were not .

.. . A m d e l of the system was c a l i b r a t e d based on f i e l d measurements*at a

nearby c o a s t a l site no t a f f e c t e d by t he power p lant . Condit ions repre-

s e n t i n g the power p l a n t (entrainment and heated e f f l u e n t ) were then imposed

and the biomass of f i s h and s h e l l f i s h were simulated. The simulated output

was then t e s t e d a g a i n s t sampling da ta from the power p lan t s i t e . The m d e l

was used to sepa ra te the e f f e c t s of t u r b i d i t y and temperature a s a spec t s of

t h e d ischarge plume, t o examine the p o t e n t i a l impact of adding a t h i r d

power gene ra t ing u n i t , modifying the c i r c u l a t i o n r a t e , and u t i l i z i n g

closed-cycle cooling. An accompanying hydrodynamic m d e l made it poss ib le

t o apply the s p a t i a l l y averaged ecosystem model to the e n t i r e a f f e c t e d

area .

Kemp (1977) es t imated primary p roduc t iv i ty (PI and r e s p i r a t i o n (R)

over a aeagrass community based on d i u r n a l (24 h r ) oxygen measurements.

H i s c a l c u l a t i o n s were complicated by s t r a t i f i c a t i o n . H i s d i scuss ion of h i s

problems and solutions may be app l i cab le t o t h e Myakka s i t u a t i o n in which

s t r a t i f i c a t i o n sometimes occurs downriver.

Browder developed an energy flow w d e l f o r the Calcasieu Lake es tua ry

i n Louisiana (Dow and Browder 1987) The m d e l t r e a t s the open es tua ry

a s r e p r e s e n t a t i v e of the e n t i r e system and Pakes o f f s h o r e h a r v e s t s of

ahrimp, menhaden, w d bottom f i s h func t ions of inshore biomass d e n s i t i e s .

New r e c r u i t s t o t h e popula t ions a r e i n j e c t e d i n t o the w d e l in seasonal

p u l s e s es t imated on the b a s i s o f what is known about the s e a s o n a l i t y of

spawning of the major spec ies in each t r o p h i c group. Growth r a t e s of

in shore popula t ions are dependent no t on ly upon a v a i l a b l e food but a l s o on

average bay temperature w d ~ a l i n i t y , which vary seasonal ly . Food avai la -

b i l i t y is fundamentally dependent upon n u t r i e n t concent ra t ions in the

e s t u a r y , which a r e assumed to be a funct ion of r i v e r flow, and on d e t r i t a l -. imports from ex tens ive marshes bordering the estuary. Monthly average

n u t r i e n t w n c e n t r a t i o n s , which s t imula te primary production by

phytoplankton, a r e assumed to be p ropor t iona l to the flow of the Calcasieu

River. Monthly e s t ima tes of d e t r i t a l b p u t were provided by David Dow

(NASA, Bay S t . Louis, pers . wmm.), who is working on a production capaci ty

model to e s t i m a t e long-term d e t r i t a l export from the marsh a s a funct ion of

a r e a l coverage by marsh vegeta t ion and the p a t t e r n of land w d water in the

marsh. Ul t imate ly , t h e e s t u a r i n e ecosystem w d e l and the marsh

productive-capaci ty m d e l w i l l be w u p l e d , and the wup led w d e l s w i l l be

used t o eva lua te the e f f e c t of marshland l o s s on f i s h e r y harves ts . The

ecosystem w d e l p resen t ly is being c a l i b r a t e d with one year of harves t

da ta . Its p r e d i c t i o n s w i l l be t e s t e d aga ins t a second year of harves t

d a t a ; however a c lose correspondence between simulated and a c t u a l da ta is

n o t expected due to numerous i n s u f f i c i e n c i e s in the input da ta .

The m d e l s of Apalachicola Bay, C r y s t a l River , Chesapeake Bay, and

Calcas ieu Lake a r e a l l of the same genera l type. They a r e "energy c i r c u i t "

o r "energy flow" w d e l s of a b a s i c cons t ruc t introduced by Odum (1982).

S t r u c t u r a l l y , t he w d e l i s a s e t of wmpartments r ep resen t ing biomass con-

nec ted by l i n e s r ep resen t ing flows of energy and/or ma te r i a l s . Energy

f l o w through the system from prey t o predator and is l o s t from the system

a s r e s p i r a t i o n o r through harvest ing. Nu t r i en t s cyc le through the system,

be ing incorpora ted i n t o o rgan ic matter through photosynthesis and being

r e l e a s e d through r e s p i r a t i o n . The r a t e of biomass flow from prey t o

p reda to r u s u a l l y is p ropor t iona l to the product of prey biomass and preda-

t o r biomass. The genera l modeling approach al lows f o r feedback e f f e c t s and . t hus these w d e l s can be highly nonl inear . They a r e no t eolved analy t i -

, c a l l y but r a t h e r by numerical i n t e g r a t i o n over time.

T h i s gene ra l scheme has v a r i a t i o n s . For ins t ance , t o c a l i b r a t e his

model, Kemp (1977 and 1980) c a l c u l a t e d the energy requi red to support a

measured l e v e l of predator biomass and p a r t i t i o n e d the flow of mergy from

a l t e r n a t i v e prey according to an a n a l y s i s of contents of the predators '

stomachs, r a t h e r than making feeding p ropor t iona l to prey biomass.

In the Calcasieu w d e l and a w d e l of the o f f s h o r e Gulf of Mexico

(Browder 19831, Browder es t imated feeding r a t e s based on e t e rgy require-

ments us ing an i t e r a t i v e "top down" flow balancing procedure in which

c a l c u l a t i o n s began with harves t l e v e l s and s tanding s tocks of the top pre-

da to r s . Biomass flows t o each p reda to r were apport ioned among prey

according t o t h e i r r e l a t i v e biomass dens i ty . A "weighting" funct ion was

u t i l i z e d to approximate s e l e c t i v i t y o r a c c e s s i b i l i t y , making i t poss ib le

f o r the w d e l t o r e f l e c t t he tendency of animals to feed on c e r t a i n prey

items over o t h e r s a t a g r e a t e r r a t e than m u l d be expected from t h e i r r e l a -

t i v e biomass d e n s i t i e s in the environment. For example, t h e r e is a ten-

dency of many benth ic feeding animals who eat both benth ic organisms and

d e t r i t u s t o feed wre heavi ly on the organisms than on the d e t r i t u s re la-

t i v e to the biomass dens i ty of both. The weighting f a c t o r usua l ly can only

be g r o s s l y es t imated f o r lack o f f i e l d s t u d i e s i n which the r e l a t i v e

biomass dens i ty of a l t e r n a t i v e prey i s measured in both t h e p reda to r ' s s to-

mach and the h a b i t a t in which it was feeding.

I d i s c u s s these d e t a i l s of the preceding four w d e l s because I am

n e x t going to d e s c r i b e a m d e l t h a t , though it sha res the food web s t ruc-

t u r e of the previous models, is in some ways very d i f f e r e n t from them.

Bigelow e t a 1 (1977) prepared a model to eva lua te the p o t e n t i a l e f f e c t

sf a planned conversion of the Oosterschledge e s tua ry in the Netherlands

i n t o a freshwater l ake by t h e cons t ruc t ion of a dam ac ross i ts connection

t o t h e North Sea. The d a m was seen a s a so lu t ion to the problem of

d i s a s t r o u s f looding from the sea.

For modeling purposes, t h e system was subdivided in two ways. F i r s t ,

t h e 2,400 s p e c i e s of l i v i n g organisms found in i t were divided in to ecolo-

g i c a l groups based on t h e i r gene ra l ecology. Secondly, space was divided

i n t o bmogeneous u n i t s def ined by where the eco log ica l groups l i v e and

feed. The modelers def ined 18 e c o l o g i c a l groups, beginning with photo-

s y n t h e t i c organisms and ending with benthos-eating b i r d s ( s e e Table 11).

The four segments def ined f o r the Oosterschelde were pe lag ic (water

column); o y s t e r banks and mussel beds; t i d a l f l a t s and shal low bottoms,

from mean high water l e v e l down to 3 m below mean low water; and deep bot-

toms, more than 3 m below low water (deep benth ic segment).

The model b a s i c a l l y is an accounting system t h a t uses ash f r e e dry

weight a s the accounting u n i t . Both the energy a v a i l a b l e t o a consumer and

t h e energy expended in r e s p i r a t i o n a r e roughly equ iva len t to ash-free dry

weight. A food web forms the s t r u c t u r e of the accounting network. Three

types o f groups were defined: one f o r photosynthet ic organisms, a second

f o r d e t r i t u s , and a t h i r d f o r he tero t rophs . Each of these is handled

s l i g h t l y d i f f e r e n t l y in the accounting system.

The m d e l s e l e c t s a s i n g l e , unique "ecostate". Ecos ta t e is a s p e c i a l

condi t ion of s teady s t a t e . A system i s in s teady s t a t e when system inflows

equa l system outf lows and the weight of each eco log ica l group is n e i t h e r

inc reaa ing o r decreasing. Ecos ta te , a s def ined by Bigelow e t a l , is the

Table 11. Eco log ica l groups def ined f o r t h e Oosterschelde e s t u a r y ecosystem (from Bigelow et a1 1977).

Photos~nthetic organisms (phytoplankton, benthic diatoms, sea grasses. and seaweeds,. Detritus (dead organic material), bacteria, micro- and meiofauna. Zooplankton and planktonic larvae of various creatures (oyste1.s. mussels. cockles, lugworms, all have planktonic larvae). Oysters and mussels. Cockles and limpets. Selective deposit feeders having planktonic larvae. Shrimp, shore crab. Sea stars. Deposit feeders having nonplanktonic larvae, and filter-feeding worms. Omnivores and infaunal predators. Benthic grazers (e.g.. periwinkles). Planktivorous fish (e.g.. anchovy, herring, sprat). Benthoseating fish (e.g.. eel, plaice, sole, dab, flounder). Fish-eating fish (e.g., mackerel, cod, whiting). Planteating fish (e.g.. mullet). Fish-eating birds (e.g., grebe). Planteating birds (e.g., mallard, teal). Benthoseating birds (e.g.. oystercatcher, plover).

unique s teady s t a t e t h a t s a t i s f i e s an "ecologica l minimum pr inc ip le" .

Computationally, t h i s s t a t e is a t t a i n e d by means of a "Gibbs funct ion", . * . which is based on Gibbe f r e e energy concept. Solu t ion involves es t imat ion

of t h e c o e f f i c i e n t s t h a t determine the amount of energy each predator takes

from a l t e r n a t i v e prey. Within c e r t a i n phys io log ica l ly based c o n s t r a i n t s ,

t h e m d e l so lves f o r the s teady s t a t e condi t ion i n which t h e r e is a n e t

energy gain to each predator from i ts predat ion . There is usua l ly only one

s o l u t i o n o r a c l u s t e r e d group of s o l u t i o n s that f i t within a narrow range.

Feeding r a t e s a r e assumed to be p ropor t iona l t o the product of the biomass

o f t h e predator and the prey. Th i s is another approach t o determining

feed ing r a t e s m d appor t ioning predat ion flows from s e v e r a l prey types to

t h e same predator .

An advantage to t h i s m d e l i n g approach is t h a t it is computat ional ly

s imple and r e q u i r e s very l i t t le computer t i m e . A disadvantage is t h a t it

looks only a t long term averages, ignor ing seasonal v a r i a t i o n .

References

,Bigelow, J.H.. J.C. DeHaven, C. Lk i t ze r , P. E l l e r a , and J.C.H. Peetera. 1977. P r o t e c t i n g an e s tua ry from floods-a pol icy a n s l y s i s of the Oosterschelde, Vol. 111, Assessment of long-run eco log ica l balances. Prepared f o r the Netherlands R i jkswa te ra t sa t by RAND, Santa Honica, Ca l i fo rn ia . 215 p.

Boynton, W.R. 1977. Some r e l a t i o n s h i p s between r i v e r flow, e s t u a r i n e c h a r a c t e r i s t i c s , and economics in a F l o r i d a Gulf coas t region. p 171-215 in: W. Seaman, Jr., and R. McLean (eds.). Fresh Water and the F l o r i d a coast : Southwest F lo r ida . F l o r i d a Sea Grant Report NO. 22. Southwest F l o r i d a Water Management District and F l o r i d a Sea Grant.

Browder, J.A. 1983. A s imula t ion model of a near-shore marine ecosystem o f the nor th-cent ra l Gulf of Mexico. p 179-222 in : K. Turgeon (ed.). Marine Ecosystem Modeling. National Environmental S a t e l l i t e , Data, and Information Service , NOAA, U.S. Dept. Corn.

Dow, D.D., J.A. Browder, and A.L. Fr ick . 1987. Modeling the e f f e c t s of c o a s t a l change on marine resources . in Proceedings of the Eighth Annual Meeting of the Socie ty of Wetland S c i e n t i s t s , S e a t t l e , Washington. May 26-29, 1987. --

Kemp, W.M. 1977. Energy a n a l y s i s and ecologic.al evalua t ion of a c o a s t a l power p lan t . Ph.D. Dis se r t a t ion . Univers i ty of F l o r i d a , Gainesvi l le .

Kemp, W.M. 1980. Energy a n a l y s i s and eco log ica l impact assessment: a case s tudy o f a c o a s t a l power p l a n t in F l o r i d a . p 225-239 in: L.D. Jensen (ed. ). I s sues Associated with Impact Assessment. Proc. 5 th National Workshop on Entrainment and Impingement. May 5-7, 1980, San Francisco , Ca l i fo rn ia . Sponsored by Ecologica l Analysts , Inc., and E l e c t r i c Power Research I n s t .

Kemp, W.M., W.R. Boynton, and A.J. Hernann. 1983. A s imula t ion m d e l i n g framework f o r eco log ica l r e sea rch in complex systems: the case of sub- merged vegeta t ion in Upper Chesapeake Bay. p 131-158 in: K.W. Turgeon (ed.). Marine Ecosystem Modeling. National Environmental S a t e l l i t e , Data, and Information Service , NOM, U.S. Dept. Comm.

Kemp, W.M., W.R. Boynton, J.C. Stevenson, and J.C. Means (eds.). 1981. Submerged Aquatic Vegetation in Chesapeake Bay. Univ. Maryland Center Environ. Estuar . STud. Ref. No. 80-168. Cambridge, Md.

Odum, H.T. 1982. Systems. Wiley, New York. 644 p.

'PROPOSED WORK

-.. The Phase I and Phase I1 r e p o r t s were used a s the b a s i s f o r the design

o f an ecosystem study t o address major ques t ions about the r i v e r t h a t w i l l

improve our a b i l i t y t o determine the most l i k e l y responses of r i v e r eco-

systems t o var ious expected o r proposed land use o r water management

changes in the Myakka basin. I propose a study of f i v e elements: (1)

modeling, ( 2 ) mapping, ( 3 ) f i e l d s t u d i e s , ( 4 ) a l abora to ry microcosm study,

and ( 5 ) s t a t i s t i c a l a n a l y s i s .

1. Modeling

Ecosystem modeling should be done in f i v e s t eps .

A. F i r s t , a mncep tua l model should be designed to a i d in m n r

munication between i n v e s t i g a t o r s and managers and to he lp in i n i t i a l study

des ign . The model should inc lude the major f e a t u r e s of the r i v e r system

t h a t might be expected t o be a f f e c t e d , e i t h e r d i r e c t l y o r i n d i r e c t l y , by

changes in water flow o r n u t r i e n t concent ra t ions .

B. Second, a s i m p l i f i e d version of t h e m n c e p t u a l model should be

q u a n t i f i e d based on e x i s t i n g information, making g ross e s t ima tes , where

necessary , and u t i l i z i n g information from o t h e r a r e a s to f i l l gaps where no

information on the Myakka River is a v a i l a b l e . Model q u a n t i f i c a t i o n and

s imula t ions can provide pe r spec t ive with which to eva lua te the i n i t i a l

assumptions used to design t h e f i e l d s t u d i e s , g iv ing guidance on b w t o

f i n e tune them.

C. Pollowing a c q u i s i t i o n o f da ta from proposed mapping and f i e l d s tu-

d i e s , t h e model w u l d be r e f i n e d and requan t i f i ed .

D. To test the w d e l , s imula t ion r e s u l t s would be compared with

a c t u a l da ta no t used in the w d e l . Co l l ec t ion of two y e a r s of pe r iod ic

-(+referably monthly) da ta w i l l a l low c o e f f i c i e n t s t o be s e t with the I i r s t

pea r of d a t a and t h e m d e l t o be t e s t e d wi th the second year of data.

E. The t e s t e d m d e l should then be used to p r e d i c t how the r i v e r eco-

systems may respond to increased concent ra t ions of n i t rogen and organic

d e t r i t u s .

Gne aspec t o f the m d e l w u l d emphasize r e l a t i o n s h i p s between n i t rogen

concen t ra t ion , primary p r o d u c t i v i t y , oxygen evolu t ion and uptake, and

b e n t h i c secondary production. In i n t e g r a t i n g the various types of infor -

mation, t h e p r i n c i p l e concerns w i l l be (1) the e f f e c t on phytoplankton of

inc reased o r decreased n i t rogen concen t ra t ions , ( 2 ) t he e f f e c t of increased

o r decreased n u t r i e n t and o rgan ic d e t r i t u s l e v e l s on submerged aqua t i c

vege ta t ion , both upstream and downstream, and d i s so lved oxygen (DO) l e v e l s

i n bottom waters; ( 3 ) t he e f f e c t of increased o r decreased oxygen l e v e l s on

b e n t h i c biomass; and ( 4 ) t h e e f f e c t of increased o r decreased benth ic

biomass on f i s h , p a r t i c u l a r l y the hogchoker . Another aspect of modeling work would emphasize r e l a t i o n s h i p s between

r i v e r flow, s a l i n i t y , benth ic spec ies and biomass, and f i s h spec ies and

biomass. Seve ra l dimensions of s a l i n i t y w i l l have to be considered and

q u a n t i f i e d i n terms of freshwater inflow. These include ( 1 ) maximum and

minimum s a l i n i t i e s occur r ing within the r i v e r on low t i d e and high t i d e (2)

t h e por t ion of the r i v e r and a rea of each h a b i t a t exper iencing each s a l i -

n i t y on each excursion of the t i d e , ( 3 ) minimum and maximum s a l i n i t i e s

experienced by each loca t ion m d h a b i t a t on each excursion of the t i d e , and

(4 ) minimum and maximum s a l i n i t i e s experienced by each loca t ion m d h a b i t a t

from wet season t o dry season. We need to quant i fy fo r each loca t ion the

cumulative exposure to each s a l i n i t y over the annual reproduct ive and

growth cycle.

- .' A t h i r d aspect of w d e l i n g might look a t cu r ren t p a t t e r n s and mii ing

a s they a f f e c t e a l i n i t y d i s t r i b u t i o n s , n i t rogen concen t ra t ions , and the

t r a n s p o r t and d i s t r i b u t i o n of phytoplankton, l a r v a l f i s h , and both sub-

merged and emergent vegeta t ion .

The d a t a collected in suggested f i e l d a t u d i e s w i l l be subjec ted to

s t a t i s t i c a l a n a l y s i s and w i l l be i n t e g r a t e d with w d e l s . T e n t a t i v e l y , I

recommend an energy flow w d e l o f t h r e e l inked subsystems: upstresm d e t r i -

t u s and SAV, midstream sa l tmarsh , and downstream seagrass-phytoplankton.

Primary production and n u t r i e n t cyc l ing should be emphasized i n the marsh

submodel. Primary production and oxygen dynamics should be emphasized in

t h e two submodels of submerged systems. Such w d e l a could improve our abi-

l i t y t o eva lua te (1) t h e c a p a b i l i t y of t h e emergent vegeta t ion to absorb

n u t r i e n t s and (2) the s e n s i t i v i t y of bottom-water oxygen concent ra t ions to

t h e combination of l o s s of seagrass and increased inpu t s of o rgan ic

ma te r i a l .

Simple w d e l i n g m r k t o guide the design of f i e l d s t u d i e s , i n t e g r a t e

d a t a , and genera te a b l i s t i c view of the r i v e r a s a ecosystem could be

va luab le to the s tudy e f f o r t . I used a conceptual ecosystem w d e l a s a

framevork f o r reviewing the Phase I and Phase I1 r e p o r t s and fo r deter-

mining t h e elements of proposed w r k . The development of simple energy

budgets based on ecosystem w d e l s of each mejor h a b i t a t w u l d be h e l p f u l in

e v a l u a t i n g var ious hypotheses about t h e system t h a t a r e the b a s i s f o r some

sugges ted uork. For ins t ance , which vegeta t ion communities of t h e r i v e r

t a k e up s u f f i c i e n t q u a n t i t i e s of n i t r o g e n to be important to the n i t rogen

m n c e n t r a t i o n s o f the r i v e r ? Do any submerged a q u a t i c vegetat ion wm-

= u n i t i e s have an important e f f e c t on the d issolved oxygen of bottom waters ,

_apd under what m n d i t i o n s (day, n i g h t , s t r a t i f i e d , mixed, e t c . ) ? Once

mapping of t h e vegeta t ion communities is completed aad acreage da ta h

ob ta ined , simple models p r e l i m i n a r i l y quan t i f i ed with a d d i t i o n a l da ta from

o t h e r l o c a t i o n s can be used t o address these quest ions. Answers baaed on

t h e pre l iminary da ta can improve t h e e f f e c t i v e n e s s of f i e l d work by r u l i n g

o u t some hypotheses and suppor t ing o t h e r s , a l lowing re sea rch resources t o

be r e d i r e c t e d accordingly. Improved da ta from f i e l d work can then rep lace

pre l iminary e s t ima tes used in models t o improve the r e l i a b i l i t y of w d e l i n g

r e s u l t s .

In add i t ion to the ecosystem model, I suggest the development of

a umdel t h a t p r e d i c t s s a l i n i t i e s a t each loca t ion in the r i v e r on each

s t a g e of the t i d e f o r incremental freshwater inf low r a t e s ranging from zero

t o t h e h ighes t recorded flow in the r i v e r . The output o f t h i s w d e l should

be used a s input t o populat ion w d e l s f o r one o r two spec ies of f i s h in

which growth and s u r v i v a l a r e func t ions o f s a l i n i t y , each epc ies having a

d i f f e r e n t set of s a l i n i t y optima t h a t vary by l i f e s tage . I n i t i a l l y , t hese

models would be e n t i r e l y t h e o r e t i c a l and baaed on hypo the t i ca l data. T e s t s

chould then be made of the t h e o r e t i c a l e f f e c t on abundance and biomass of

reducing o r inc reas ing r i v e r inf low t o var ious e x t e n t s .

2. Napping

The f i r s t e s s e n t i a l s t e p in ga the r ing a d d i t i o n a l information is a

p r o j e c t t o map aad quant i fy t h e d i f f e r e n t h a b i t a t s of the r i v e r by vegeta-

t i o n type aud depth. The map should be r e s t r i c t e d to vegetat ion t h a t is

f looded a t l e a s t seaaonally. It should inc lude a l l marsh vegetat ion

connected to the r i v e r during a t l e a s t some t i m e of t h e year. The loca t ion

-and a r e a l ex ten t o f the seagrass beds in the lower r i v e r should be pneci-

s e l y determined. Also, a good es t ima te of the percent coverage o f r i v e r

bottom by submerged a q u a t i c vegeta t ion should be obta ined by ha l f m i l e

r i v e r zone (or a rea between e x i s t i n g t r a n s e c t s ) throughout t h e r i v e r .

A e r i a l photography and the vegetat ion t r a n s e c t s developed during the Phase

I s tudy could se rve a s the b a s i s f o r the map. Addi t ional f i e l d measure-

ments ~ u l d be necessary to adequately map seagrasses in the lower r i v e r .

Some f i e l d work may a l s o be needed to map SAV i n the upper r i v e r .

3. Sampling

The sampling s t r a t e g y should be to take advantage of s p a t i a l and

seasona l v a r i a t i o n to e s t ima te (1) how s a l i n i t y v a r i e s a s a funct ion of

f reshwater inf low and o the r v a r i a b l e s ; ( 2 ) how phytoplankton concent ra t ions

change a s a funct ion of freshwater inf low and n i t rogen concent ra t ion; (3)

bottom dissolved oxygen changes a s a funct ion of s a l i n i t y ( o r

s t r a t i f i c a t i o n ) , phytoplankton concent ra t ion , o rgan ic content of sediment,

p a r t i c u l a t e concent ra t ion of water , and coverage and biomass of SAV: ( 4 )

how SAV v a r i e s a s a funct ion of s a l i n i t y , phytoplankton concent ra t ion ,

c o l o r , and POC; ( 5 ) how benthic i n v e r t e b r a t e dens i ty and biomass (and

poss ib ly , growth r a t e ) vary a s a funct ion of s a l i n i t y , h a b i t a t , and

d i s so lved oxygen M) in bottom waters; and ( 6 ) how f i s h abundances vary a s a

func t ion of s a l i n i t y and ben th ic i n v e r t e b r a t e biomass. Care fu l loca t ion of

s t a t i o n s and a sampling i n t e n s i t y t h a t adequately covers the s p a t i a l w d

temporal v a r i a t i o n in these f a c t o r s w i l l be important to the success of the

study. The background of information provided by the Phase I and Phase I1

s t u d i e s w i l l be p a r t i c u l a r l y va luable in s e l e c t i n g s t a t i o n s and scheduling

-ampling.

S t a t i o n l o c a t i o n s in the r i v e r should coinc ide with those used in

Phase I and Phase I1 s t u d i e s and should be chosen to r ep resen t the various

s e c t i o n s of t h e r i v e r def ined in these s t u d i e s . Addi t ional eampling ata-

t i o n a should be e s t a b l i s h e d in the t r i b u t a r i e s t o Myakka River such a s Deer

P r a i r i e Creek, Big Slough, Warm Mineral Spr ings , and the t r i b u t a r y near

Warm Mineral Spr ings t h a t is ad jacen t t o a sewage d i sposa l s i t e .

P resen t v a r i a t i o n in n i t rogen w n c e n t r a t i o n s and o t h e r condi t ions between

t r i b u t a r y and r i v e r sites w i l l he lp us t o eva lua te e f f e c t s of n i t rogen

concen t ra t ions . Fu tu re d i f f e r e n c e s between t r i b u t a r y and r i v e r s i t e s may

s e r v e a s an index of management e f f e c t s on the r i v e r . Determining the

r e l a t i o n s h i p between n i t rogen concen t ra t ions and r i v e r flow r a t e e o r rain-

f a l l could help us s e p a r a t e the e f f e c t of man's a c t i v i t i e s from n a t u r a l

v a r i a t i o n . POC and co lo r , a s we l l as n i t r o g e n , in the t r i b u t a r y and r i v e r

s i tes should be compared. The t r i b u t a r y near the sewage d i sposa l s i t e may

provide the oppor tuni ty t o eva lua te cond i t ions in an a rea t h a t p r e s e n t l y

has higher n i t rogen concen t ra t ions than the r i v e r o r the o t h e r t r i b u t a r i e s .

To t h e e x t e n t p o s s i b l e , an e f f o r t should be made to s e l e c t t r i b u t a r y and

r i v e r s i t e s t h a t experience approximately the same s a l i n i t y regimes. Th i s

w i l l minimize poss ib le confounding e f f e c t s of s a l i n i t y d i f f e r e n c e s when

a t t empt ing to determine r e l a t i o n s h i p s between the o t h e r parameters.

To the ex ten t p o s s i b l e , sampling and measurement of a l l requi red para-

meters should rake p lace synchronously to f a c i l i t a t e the determinat ion of

r e l a t i o n s h i p s between them. Sampling of a l l l i v i n g organisms should be on

a m i t a r e a bas is . Ash-free dry weights should be obta ined f o r a l l major

b i o l o g i c a l components sampled. A t l e a s t t h r e e .samples o r measurements of

each type should be taken on each s t a t i o n vlsit to f a c i l i t a t e s t a t i s t i c a l . - .. analyses . To adequately i n v e s t i g a t e v a r i a t i o n within the year , sampling

should be conducted monthly. o r a t l e a s t bimonthly. Sampling should be

conducted f o r a t l e a s t two yea r s and, p re fe rab ly , t h r e e years .

Continue and expand s a l i n i t y sampling aonducted f o r the Phase I and

Phase I1 r e p o r t s so t h a t t he l eng th and pos i t ion of t i d a l excursions and

t h e v a r i a t i o n in s a l i n i t y a t each loca t ion is determined f o r many Myakka

River flow r a t e s , Peace River flow r a t e s , and, poss ib ly , wind speeds.

Measure s a l i n i t y end s t a g e on both high and low t i d e s and a t in termedia te

t i d e s . Measure c u r r e n t s (speed and d i r e c t i o n a t s e v e r a l depths) over the

t i d a l cycle a t key s t a t i o n s .

Insu re t h a t w n i t o r i n g of sea s t a g e is continued a t St . Petersburg or

i n i t i a t e sampling a t an ocean s t a t i o n near Char lo t t e Harbor-preferably one - t h a t is n o t a f f e c t e d by l o c a l freshwater h f l o w . A recording s t age s t a t i o n

i n C h a r l o t t e Harbor a l s o w u l d be d e s i r a b l e .

Determine how n i t rogen concent ra t ions vary over time a t r i v e r and tri-

bu ta ry s i t e s . Sample once a w n t h o r every o t h e r w n t h to determine seaso-

n a l va r i a t ion . Sample a t l e a s t twice within each w n t h to determine the

e f f e c t of s p r i n g and neap t i d e s . Sample over the t i d a l cycle. Sample in

conjunct ion with phytoplankton c o l l e c t i o n s . Measure a l l spec ies of n i t r o -

gen, a s in Phase I and Phase I1 s t u d i e s . Measure s a l i n i t y concurrent ly.

Determine lww phytoplankton concen t ra t ions and g ross taxonomic c o w

p o s i t i o n (count c e l l s by s i z e f r a c t i o n ) vary over time a t r i v e r and t r ibu -

t a r y s t a t i o n s . Sample every q n t h o r every o the r month. Sample twice

wi th in each sampling month to determine how concentrat ions change with

-spring and neap t i d e s . Sample over t i d a l cycle. Col lec t phytoplankton

samples in conjunction with ni trogen measurements.

Determine change in DO over time with l i g h t and dark b o t t l e experi-

ments a t s i t e s of phytoplankton w d ni t rogen measurements. Estimate pri-

mary product iv i ty and r e s p i r a t i o n in the water column on b a s i s of l i gh t -

dark b o t t l e measurements.

Light transmission should be measured wncur ren t ly with phytoplankton

sampling. Color and POC should a l s o be measured ao t h a t a l i g h t extension

c o e f f i c i e n t can be estimated a s a funct ion of color. POC, and phytoplankton

c e l l concentrat ions.

Note: In ana lys i s , n i t r a t e a i t r i t e and amonia should be examined separa-

t e l y f o r t h e i r e f f e c t s on primary product iv i ty , because Sklar ( 1 9 7 6 ) .

working a t the m u t h of the Miss iss ippi River, found t h a t phytoplankton

primary product iv i ty was s i g n i f i c a n t l y r e l a t e d to n i t r a t e a i t r i t e - n i t r o g e n

but no t to ammonia-nitrogen.

Determine how the biomass and gross taxonomic composition of zooplank-

ton v a r i e s in t i m e and space r e l a t i v e to the biomass of phytoplankton by

sampling a t t he same time and p lace as phytoplankton sampling.

Sample ichthyoplankton concurrent ly with phytoplankton and zooplankton

sampling.

In phytoplankton, zooplankton, and ichthyoplankton t o w s , s tandardize

tow speed w d time towed w d use flow meters t o est i lnate wlume of water

f i l t e r e d .

Conduct a primary production and n u t r i e n t cycl ing study of p r i n c i p a l - .. . s p e c i e s of emergent macrophytes (Juncus, poss ib ly a l s o Sc i rpus and *. Locate sampling p l o t s a t d i f f e r e n t sites r e l a t i v e to r i v e r flow ( f o r

i n s t a n c e a t t he upper m d lower ends of t h e braided r i v e r a r e a ) so t h a t

s e c t i o n s poss ib ly exposed to d i f f e r e n t concen t ra t ions of n u t r i e n t s can be

compared.

Conduct a primary production and oxygen evolu t ion study of p r i n c i p a l

s p e c i e s of seagrasses (Halodule w r i g h t i i ) in Lower Myakka Bay o r Upper

C h a r l o t t e Harbor. Inc lude ambient l i g h t and l i g h t t ransmission a s measured

v a r i a b l e s . Measure oxygen l e v e l s over a 24-hr period.

Conduct a primary production, oxygen evo lu t ion , and n u t r i e n t uptake

and cyc l ing study of SAV i n upper r i v e r . Measure oxygen l e v e l s over 24-hr

period. Take r e p l i c a t e samples t o f a c i l i t a t e s t a t i s t i c a l a n a l y s i s to

s e p a r a t e the e f f e c t of d i f f e r e n t v a r i a b l e s and t o compare d i f f e r e n c e s among

s i t e s .

Conduct sampling to determine the r e l a t i o n s h i p between the benthos

(dens i ty , biomass, t smnomic compostion, r e s p i r a t i o n r a t e , e t c ) m d bottom

DO concen t ra t ions in bottom waters . Inc lude 24-hr measurements of

d iseolved oxygen a t s i tes o f sampling. Consider water flow r a t e s , type of

t i d e ( sp r ing o r neap), and t i d a l s t a g e a s poss ib le in f luenc ing f a c t o r s .

Measure s a l i n i t y t o cover m o t h e r important f a c t o r inf luencing benthos. I f

f e a s i b l e , s e p a r a t e benth ic organisms i n t o depos i t f eede r s and f i l t e r

f e e d e r s and ob ta in s e p a r a t e ash-free dry weights on the two groups.

Conduct sampling to de te rv ine the v a r i a t i o n in benth ic denai ty ,

biomass, and g ross taxonomic composition, by h a b i t a t ( sa l tmarsh , s eagrass ,

.oyster bed, e t c . ) , in the d i f f e r e n t s e c t i o n s of t h e r i v e r (upr ive r , bsaided

r i v e r , Hyakka Bay, Upper Char lo t t e Harbor). Organic content in eediments

a t t h e site of benth ic sampling should be determined. T h i s i n v e s t i g a t i o n

and the previous one (i.e., de termins t ion of r e l a t i o n s h i p between benthos

and DO) can be i n t e g r a t e d by a sampling design t h a t covers the spectrum of

h a b i t a t s and a range of DO l e v e l s occur r ing wi th in each of one o r m r e

h a b i t a t s ( i .e . , bare bottom and g r a s s bottom). Repl ica te samples s b u l d be

taken. Analys is can then s e p a r a t e oxygen and h a b i t a t e f f e c t s .

Determine the s p e c i e s composition and dens i ty of f i s h (and poss ib ly

a l s o mscrocrustaceans) in marsh h a b i t a t s , such a s the oxbows and the

bra ided r i v e r sec t ion . It is e s p e c i a l l y important to determine the use of

t h i s type of a r e a by e a r l y se t t l emen t s t a g e s of r e c r e a t i o n a l l y and mmmer-

c i a l l y important f i s h and mscrocrustaceans.

Determine t h e food h a b i t s of t h e h g c h o k e r , T r i n e c t e s maculatus, in

t h e Myakka River. Although mentioned in food h a b i t s s t u d i e s , t h i s spec ies

has no t been w e l l covered, p r i n c i p a l l y because w few specimens were caught

in these s t u d i e s and a l s o because a very high proport ion of those caught

had empty stomachs. Since t h i s spec ies makes up euch a high proport ion of

t h e f i s h community in Myakka River and, a d d i t i o n a l l y , because it appears t o

be e n t i r e l y dependent upon t h e r i v e r environment f o r i t s food, it is impor-

t a n t t o b e t t e r determine what it is e a t i n g in the r i v e r .

Conduct s tandardized t r awl sampling a t a t l e a s t f i v e genera l l o c a t i o n s

i n the r i v e r , as in the Phase I and Phase 11 s t u d i e s . Conduct sampling a t

n i g h t on the new w o n , a s in tbe previous s tud ies . Sample around high

t i d e . Measure cross-sec t ional a rea of t r awl w d d i s t a n c e swept a t a known

- t h r o t t l e s e t t i n g so t h a t c a t c h can be expressed on a u n i t a rea basis . -

Because hogchoker a r e m abundant in the r i v e r and a l s o because they a r e

e n t i r e l y dependent upon the r i v e r , hogchoker d e n s i t i e s in the r i v e r can be

used a s an index of t h e well-being of r i v e r ecosystems a s they p resen t ly

e x i s t . Sample once m n t h l y f o r a t l e a s t two years.

S e t up a r egu la r w n t h l y schedule f o r w-monitoring n i t rogen ( a l l

s p e c i e s ) and s a l i n i t y . Inc rease t h e number of l o c a t i o n s where n i t rogen is

measured. Locate s t a t i o n s r e l a t i v e to s t ands of various types of marsh

and submerged vege ta t ion , so t h a t n i t rogen w n c e n t r a t i o n s upstream and

domst ream of s t ands of vegeta t ion can be wmpared a s one e s t ima te of

uptake by the var ious types o f vegeta t ion . Conduct t h i s type of monitoring

f o r st l e a s t two years . The n i t rogen da ta w i l l a l low us t o determine the

p r i n c i p a l l o c a t i o n s where uptake occurs . The s a l i n i t y d a t a w i l l a l low

determinat ion of t h e e f f e c t on n i t rogen w n c e n t r a t l o n of mixing of r i v e r

and C h a r l o t t e Harbor waters. Add i t iona l ly , t h e s a l i n i t y d a t a w i l l allow

e f f e c t s of s a l i n i t y t o be separa ted from e f f e c t s of o t h e r v a r i a b l e s of

i n t e r e s t such a s n i t rogen on b i o l o g i c a l parameters.

Nu t r i en t concen t ra t ions a r e a funct ion of uptake and mixing. S a l i n i t y

i s w Index of the degree of mixing and can be used to e s t ima te the change

in t h e concent ra t ion of a n u t r i e n t t h a t occurs in response to mixing alone.

Therefore , s a l i n i t y w n i t o r i n g dl1 enhance the s tudy of n i t rogen dynamics.

The Phase I and Phase I1 s t u d i e s have suggested t h a t s a l i n i t y , par-

t i c u l a r l y over the long term, has an important Inf luence over both vegeta-

t i o n m d t h e benthos. It w i l l be necessary t o know the h i s t o r y of s a l i n i t y

a t each site to s e p a r a t e the e f f e c t s of s a l i n i t y from (1) the e f f e c t s of

oxygen on ben th ic biomass, (2 ) t h e e f f e c t of S h V coverage on d issolved oxy-

- .. gen l e v e l s , and ( 3 ) t h e e f f e c t o f marsh vegeta t ion type on n u t r i e n t uptake.

I d e a l l y , t h e same sampling s t a t i o n s e s t a b l i s h e d in the Phase I and

Phase I1 s t u d i e s should be used, provid ing t h e sites of benth ic sampling

and primary p roduc t iv i ty s t u d i e s a r e included in these.

Table 1 summarizes suggested f i e l d s t u d i e s , l i s t i n g t h e parameters

t h a t should be measured and suggested frequency of measurements and indi-

c a t i n g those parameters t h a t should be measured synchronously.

S t r a t i f i c a t i o n of the r i v e r is a major f a c t o r a f f e c t i n g bottom oxygen.

It is important to determine uuder what circumstances s t r a t i f i c a t i o n occurs

and the l o c a t i o n and a r e a l ex ten t o f i ts occurrence. What r i v e r flow r a t e

i n i t i a t e s s t r a t i f i c a t i o n ? What cond i t ions must e x i s t in Char lo t t e Harbor

i n o rde r f o r e t r a t i f i c a t i o n to occur? Row o f t e n does i t occur? Is it a

f r equen t o r unusual event? What l o c a t i o n s a r e anoxic during a s t r a t i f i c a -

t i o n event? What acreage of bottom water is a£ f e c t e d a t each s i t e ? Are

t h e same sites a f f e c t e d repeatedly? We need to know m r e about t h i s

phenomenon. A s p e c i a l a n c i l l a r y sampling e f f o r t in conjunction with the

sampling design o u t l i n e may be needed to gain t h i s information. Once loca-

t i o n s and times of low oxygen a r e i d e n t i f i e d , e p e c i a l sampling should be

conducted to determine a r e a l ex ten t and durat ion. There a l s o i s s need to

know t h e l o c a l i z e d a f f e c t of bottom scour ing and turbulence on the benthos.

T h i s would he lp us b e t t e r understand the d i s t r i b u t i o n of the benthos and

a l s o might he lp us better eva lua te t h e e f f e c t o f changes in water flow.

Some s p e c i a l sampling f o r benthos a t t he mouths of t r i b u t a r i e s might he lp

u s gain t h i s information.

I .. 4. Laboratory Microcosm Study

Conduct a l abora to ry microcosm study with water from various l o c a t i o n s

i n Myakka River. Add con t ro l l ed q u a n t i t i e s o f n i t rogen and measure system

response i n terms of phytoplankton c e l l concent ra t ions , g ross taxonomic

composition, and transparency. D i s t i n g u i s h e f f e c t s of inorganic w d orga-

n i c forms o f n i t rogen. Di s t ingu i sh e f f e c t s of ammonia and n i t r a t e - n i t r i t e .

Determine the r e l a t i o n s h i p between l i g h t t ransmission w d phytoplankton

concent ra t ion . Measure color a s a v a r i a b l e a l s o a f f e c t i n g l i g h t t ransmission.

5. S t a t i s t i c a l Analyses

S t a t i s t i c a l a n a l y s i s is an e s s e n t i a l element of the study t o determine

whether measured parameters d i f f e r s i g n i f i c a n t l y in space and time and b w

they vary r e l a t i v e to each o the r . For example, s t a t i s t i c a l t e s t s a r e

needed t o determine whether ben th ic biomass d i f f e r s s i g n i f i c a n t l y a w n g

h a b i t a t s , whether n i t rogen concen t ra t ions d i f f e r s i g n i f i c a n t l y among dif-

f e r e n t segments o f t h e r i v e r w d between the r i v e r and its t r i b u t a r i e s ,

whether d iesolved oxygen concen t ra t ions a r e s i g n i f i c a n t l y higher over

seagrasa beds than over bare bottom, e t c . To make such comparisons it is

important not only t o measure within each space-time s t r a t a but a l s o to

have two o r w r e r e p e t i t i o n s wi th in each s t r a t a .

Regression analyses should be uaed to test and quant i fy r e l a t i o n s h i p s

between v a r i a b l e s f o r which r e l a t i o n s h i p s a r e hypothesized. Both l i n e a r

and non-linear r e l a t i o n s h i p s should be explored. It msy be poss ib le to

f i n d a c l e a r s t a t i s t i c a l r e l a t i o n s h i p between n i t rogen concent ra t ions and

phytoplankton biomass o r d isso lved oxygen. A r e l a t i o n s h i p between - .' b e n t h i c biomass and d issolved oxygen is l i k e l y . Two year s of s a l i n i t y

measurements, coupled with da ta on Myakka River flow, Peace River flow, and

sea-level he igh t , could probably be used to develop n u l t i p l e regress ion

equa t ions t h a t could hind c a s t t h e s a l i n i t y h i s t o r y (i .e. , frequency a t

each s a l i n i t y ) f o r every sampling s i t e vhere the s a l i n i t y measurements were

taken. A r e p o r t by Wang and Browder ( 1 9 8 6 ) desc r ibes b w t h i s type of

e s t ima t ion was made f o r s t a t i o n s in Fakka Union Bay in southwest F lo r ida .

S t a t i s t i c a l a n a l y s i s of the da ta c o l l e c t e d in the study elements suggested

above w i l l help bu i ld a b e t t e r m d e r s t a n d i n g of the system and w i l l provide

information to quant i fy m d e l s t o genera te f u r t h e r understanding.

P r i o r i t i e s

Based on my present view of the system, I have t e n t a t i v e l y given the

f i e l d i n v e s t i g a t i o n s i temized above the fol lowing p r i o r i t i e s :

P r i o r i t y Number One

The f i r s t p r i o r i t y is t o mmple te the d e s c r i p t i o n of the s p a t i a l w d

temporal p a t t e r n of s a l i n i t i e s in t h e r i v e r a s a funct ion of Myakka River

f low and o t h e r va r i ab les . The approach i n i t i a t e d in the Phase I and Phase

I1 d i r e c t l y approaches ques t ions t h a t must be answered to adequately eva-

l u a t e e f f e c t s of land use and water management changes on n a t u r a l resources

of t h e r i v e r , but d a t a c o l l e c t i o n needs t o be expanded to cover a t l e a s t

s p r i n g and neap t i d e s of each month f o r a t l e a s t two yea r s t o be used to

understand t h e d i s t r i b u t i o n of benth ic organisms o r to p r e d i c t the e f f e c t s

of changes in f reshwater inf loy . Sampling on four t i d a l cycles each m n t h

r a t h e r than j u s t two w u l d be d e s i r a b l e . V e l o c i t i e s were not measured in

- the Phase I and Phase I1 s t u d i e s but should be added in follow-up s t u d i e s

in orde r t h a t a d e t a i l e d view o f t h e c u r r e n t p a t t e r n of the r i v e r can be

obta ined .

P r i o r i t y Number Two

A map of t h e r i v e r and q u a n t i f i c a t i o n of t h e d i f f e r e n t types of habi-

t a t , by r i v e r s e c t i o n , is extremely necessary f o r t h r e e reasons:

(1 ) t o e s t i m a t e t h e p o t e n t i a l uptake of n i t rogen by rooted vege ta t ion , a s opposed to phytoplankton.

( 2 ) t o e s t ima te the importance of SAV and seagrasses t o the d i s so lged oxygen budget of bottom waters in d i f f e r e n t segments o f the r i v e r .

( 3 ) t o e s t a b l i s h a base l ine from which to m n i t o r change in a r e a covered by SAV and aeagrasses , by r i v e r sec t ion .

P r i o r i t y Number Three

A d e t a i l e d s tudy of n i t rogen concent ra t ion in the r i v e r a s i t changes

ove r t i m e and space in r e l a t i o n t o s a l i n i t y , POC, c o l o r , near-bottom DO,

BOD, w d sediment o rgan ic content ( r e f r a c t i l e and l a b i l e ) i s a second high-

p r i o r i t y necess i ty . Using s t a t i s t i c a l a n a l y e i s , t he v a r i a t i o n in ni t rogen

concen t ra t ions over time should be examined in r e l a t i o n to the v a r i a t i o n i n

r i v e r flow o r , poss ib ly , r a i n f a l l a t t he n e a r e s t recording s t a t i o n in the

watershed. Such a s tudy w i l l show us:

( 1 ) the ex ten t to which n i t rogen concen t ra t ions vary s p a t i a l l y and temporal ly in the r i v e r now

(2 ) t h e r e l a t i o n s h i p between r i v e r flow r a t e (or r a i n f a l l ) in the watershed and n i t rogen concen t ra t ions

( 3 ) s e c t i o n s o f the r i v e r and i ts t r i b u t a r i e s where n i t rogen concen t ra t ions a r e p r e s e n t l y the h ighes t

(4) how t h e r i v e r wmpares t o i ts t r i b u t a r i e s a s n i t rogen wn- c m t r a t i o n s in both change over time

( 5 ) whether near-bottom DO concen t ra t ions a r e w r r e l a t e d wi th n i t rogen - .' concen t ra t ions

( 6 ) t he ex ten t of p o t e n t i a l d i l u t i o n a s water flows downriver and is mixed with Char lo t t e Harbor water by t h e t i d e

( 7 ) s p e c i f i c s e c t i o n s of t h e r i v e r where major uptake occurs , poss ib ly i n d i c a t i n g w important e f f e c t o f vegeta t ion

A t t he l e a s t , t h i s e f f o r t w i l l provide a base l ine f o r f u t u r e w n i -

t o r i n g of the e f f e c t o f w a s t e r a t e r r ecyc l ing , increased pas tu re runof f ,

i nc reased f e r t i l i z e r a p p l i c a t i o n , upstream water withdrawals , e t c .

S ince t h e Phase I1 s tudy suggested t h a t n i t rogen w n c e n t r a t i o n s a r e

a f f e c t e d by r a i n f a l l and, presumably, r i v e r flow, i t is necessary to quan-

t i f y t h i s r e l a t i o n s h i p in order to eva lua te the e f f e c t o f land use and

water management changes on n i t rogen concent ra t ions . Knowing the quan-

t i t a t i v e r e l a t i o n s h i p between n i t rogen concen t ra t ions and r i v e r flow o r

r a i n f a l l m u l d al low us t o aepa ra te n a t u r a l v a r i a t i o n from man's e f f e c t s .

Comparing the r e l a t i o n s h i p between r i v e r concent ra t ions and t r i b u t a r y wn-

c e n t r a t i o n s now and a f t e r the f a c i l i t y is o p e r a t i o n a l a l s o may provide an

index of t h e e f f e c t of man's a c t i v i t i e s on t h e r i v e r . It w i l l be

i n s t r u c t i v e t o compare n i t rogen w n c e n t r a t i o n s near the Warm Mineral

Spr ings package t rea tment f a c i l i t y t o those in o the r p a r t s of the r i v e r .

F inding a s t a t i s t i c a l l y s i g n i f i c a n t r e l a t i o n s h i p between n i t rogen wn-

c e n t r a t i o n s o r o rgan ic matter w n c e n t r a t i o n s and near-bottom dissolved oxy-

gen w n c e n t r a t i o n s m u l d s t rong ly suggest t h a t DO concen t ra t ions w u l d

d e c l i n e i f n i t rogen o r o rgan ic m a t e r i a l were added to the r i v e r . We could

even es t ima te the amount of d e c l i n e f o r each incremental increase .

P r i o r i t y Number Four

A d e t a i l e d i n v e s t i g a t i o n of t h e r e l a t i o n s h i p of benth ic numerical den-

-eYty, biomass-density, and g ross tsxonomic oomposition to .near-bottom-DO

concen t r s t ion , BOD, sediment o rgan ic mat ter , and h a b i t a t is t h i r d on my

l i s t of p r i o r i t i e s . Benthic d e n s i t i e s var ied tremendously among the

va r ious segments of t h e r i v e r , according to the Phase I study. S a l i n i t y

was a l i k e l y cause of much of the v a r i a t i o n , but bottom DO concent ra t ion

might have been a second determining fac to r . Low W concen t ra t ions might.

f o r example, expla in the low benth ic d e n s i t i e s in the upper p a r t of the

r i v e r . Var ia t ion i n ben th ic d e n s i t i e s among h a b i t a t s exposed to the same

s a l i n i t y regime was no t examined in the Phase I study. Th i s source o f

v a r i a t i o n must e i t h e r be explored o r avoided; o therwise , i t w i l l not be

p o s s i b l e to m d e r s t a n d r e l a t i o n s h i p s between the benthos and DO. We could

a m i d t h e i s s u e of h a b i t a t e f f e c t s by sampling only on bare bottom, a s was

done in the Char lo t t e Harbor s tudy by Estevez. But I th ink we need to

determine v a r i a t i o n among e x i s t i n g h a b i t a t s f o r s e v e r a l reasons:

( 1 ) near-bottom W concent ra t ion may be much g r e a t e r over vegetated bottom;

(2 ) benth ic dens i ty and biomass-density may be m c h g r e a t e r on vege- t a t e d bottom, a s Yokel (1975) and Weinstein et a 1 (1977) have found d e n s i t i e s t o be elsewhere;

( 3 ) coverage by bottom vegeta t ion may dec l ine due to shading by phy- toplankton when n i t rogen concen t ra t ions in the r i v e r become ele- vated.

To t h e e x t e n t p o s s i b l e , benth ic aampling sites should m i n c i d e with s i t e s

where n i t rogen et a 1 a r e being measured.

Examination of the benthos should be emphasized in f u t u r e w r k . The

s p e c i e s d i v e r s i t y , numerical dens i ty , and biomass dens i ty of the benthos

probabi ly w i l l be s e n s i t i v e i n d i c a t o r s o f t h e response of the r i v e r eco-

system to changes in land use p r a c t i c e s o r water management. For ins t ance ,

i nc reased concent ra t ions of n i t rogen and o rgan ic matter would be l i k e l y t o

-depress bottom DO concen t ra t ions and lead to a dec l ine in coverage b y SAV.

On-site r e t e n t i o n of p s s t u r e end a g r i c u l t u r a l runof f , which m u l d decrease

n i t r o g e n concen t ra t ions in the r i v e r , might lead to lower n i t rogen con-

c e n t r a t i o n s in the r i v e r and increased coverage by SAV. Benthic biomass

d e n s i t y would l i k e l y decrease i f bottom DO concen t ra t ions o r SAV coverage

decreased, whereas inc reases in these v a r i a b l e s might lead to increased

ben th ic biomass dens i ty . My t r o p h i c a n a l y s i s sugges ts t h a t the dens i ty and

p r o d u c t i v i t y of f i s h w u l d l i k e l y be a f f e c t e d by changes in benth ic

biomass.

In most ben th ic studies,taxonomic composition, d i v e r s i t y , and,

sometimes, d e n s i t y a r e examined; but measurements of benth ic biomass den-

s i t y a r e neglected. Th i s i s unfo r tuna te i f one wants t o r e l a t e the benthos

t o f i s h abundance and biomass, because the biomass dens i ty of the benthos

r e l a t e s d i r e c t l y t o energy a v a i l a b i l i t y to benthic-feeding f i s h . Benthic

d i v e r s i t y o r numerical dens i ty a r e poor I n d i c a t o r s of energy a v a i l a b i l i t y .

D i v e r s i t y i n d i c a t e s how many s p e c i e s a r e a v a i l a b l e but no t how m c h food

energy is ava i l ab le . Even numerical dens i ty is an inadequate index of food

energy a v a i l a b i l i t y , because of t h e wide v a r i s t i o n in the s i z e s of benth ic

organisms. Biomass dens i ty is t h e main q u a n t i t y t h a t should be measured

t o eva lua te p o t e n t i a l impacts of changes in the benthos on the f i s h c o w

munity. Obtaining ash-free dry weights is important , p a r t i c u l a r l y where

s h e l l s make up a cons iderable p a r t of the mass.

P r i o r i t y Number F i v e

An rnders tanding of how phytoplankton responds to ni t rogen in r i v e r

water in the e x i s t i n g range of .color and s a l i n i t y g e t s f o u r t h p r i o r i t y in

my view. In "Proposed Work", I recommended complimentary f i e l d and labora-

t b r y i n v e s t i g a t i o n s . Preferably , phytoplankton c o l l e c t i o n s tshould be-made

a t t he same s i t e a s measurements of n i t rogen , e t c .

These four i n v e s t i g a t i o n s should be i n i t i a t e d in the f i r s t phase of

new work. Resu l t s of these i n v e s t i g a t i o n s , p re fe rab ly i n t e g r a t e d with

o t h e r information in a pre l iminary model, could provide a good q u a n t i t a t i v e

i n d i c a t i o n of whether t h e o t h e r i n v e s t i g a t i o n s recommended in Proposed Work

a r e r e a l l y needed. For ins t ance , they could t e l l us

(1) whether emergent vegeta t ion in any sec t ion of t h e r i v e r could poss ib ly t ake up a s u f f i c i e n t quan t i ty of n i t rogen to be important i n maderating n i t rogen concen t ra t ions in the water eolumn

(2) whether up r ive r SAV s u b s t a n t i a l l y inc reases near-bottom DO concent ra t ions ;

(3) whether up r ive r SAV suppor t s s u b s t a n t i a l l y higher ben th ic biomass d e n s i t i e s than ad jacen t h a b i t a t s and whether t h i s makes a substan- t i a l d i f f e r e n c e t o the o v e r a l l biomass o f fe red to f i s h by the r i v e r segment;

( 4 ) whether downriver seagrasses s u b s t a n t i a l l y inc rease near-bottom DO concen t ra t ions ;

( 5 ) whether downriver seagrasses support s u b s t a n t i a l l y higher benth ic biomass d e n s i t i e s than ad jacen t h a b i t a t s and whether t h i s makes a s u b s t a n t i a l d i f f e r e n c e to the o v e r a l l biomass o f f e r e d to f i s h by t h e r i v e r segment.

Area of coverage and r a t e s of photosynthes is and n e t production w i l l be

important f a c t o r s in making these evalua t ions .

References

Browder. J .A. , and J .D . Wang. 1987. Modeling water management e f f e c t s on marine resource abundance6 in Faka Union Bay, F lo r ida . in: Proc. Symp. on the ecology and conservat ion o f wetlands o f the Usumacinta and G r i j a l v a d e l t a , V i l l a h e r m s a , Tabasco, Kexico, February 2-6, 1987. 21 p.

Skla r , F.H. 1976. Primary p roduc t iv i ty in the Miss i s s ipp i d e l t a b ight nea r a shal low bay e s t u a r i n e system in Louisiana. M.S., Louisiana S t a t e Unive r s i ty , Baton Rouge, Louisiana. 96 p.

-Weinstein, M.P, C.M. Courtney, and J.C. Kinch. 1977. The Marco Is ldhd es tuary: a summary o f physicochemical w d b i o l o g i c a l parameters. F l o r i d a S c i e n t i s t 40: 97-124.

Yokel, B.J. 1975. A comparison of animal abundance and d i s t r i b u t i o n in h a b i t a t s in Rookery Bay, Marco I s l a n d , and FaMahatchee on the south- west coas t of F lo r ida . Pre l iminary r e p o r t from Rosens t i e l School of Marine and Atmospheric Science to t h e Deltona Corp., Miami, F lor ida .

a F'arawters indicated d t h the aam letter &mld be m e d sgnchmxmly or oearsyndrmously. Actual mter depth, needed to 0x1- from a n c m t r a t h to mit arm his (nitmgm, ptymplakton, etc). Fish wedghts wuld be @tisated frw hgfh iet wigk relations md wt weighc-drp relaths

obtained by the Etudy.

1600 CITY ISLAND PARK SARASOT4 FLORIDA 34236

PHONE: ( 8 1 3 ) 3 8 8 - 4 4 4 1

September 20, 1988

Dr. Jeffrey Lincer Sarasota County Science Advisor 1301 Cattleman Road Sarasota FL 34232

Dear Jeff : I In August 1987 you received the report, "An ecosystem view of management research in the Myakka River", pre- pared by Dr. Joan Browder, NOAA/NME'S Research Ecologist.

This analysis contained much useful information on the design of future studies and our own wetland mapping and salinity model projects are the direct consequence of her recommendations.

The report also contains important guidance for other data collection efforts, such as the Myakka River and Basin Assessment you are undertaking with the DER and other agencies. Her recommendations are also relevant to the Feasibility Study underway by Dames & Moore, Inc regarding the next phase of water production and reuse on the RMR Reserve.

A pertinent discussion from Part 1 of Joan's report is attached, and I heartily recommend all of Part 4, "Pro- posed Work" to your cooperators and contractors.

Sincerely yours,

Ernest D. Estevez, Ph.D. Senior Scientist

enclosures EDE: dm

ROBERT M. JOHNSON WILLIAM R. MOTE KUMAR MAHADEVAN. Ph.0. RICHARD H PIERCE. Ph.0. CHAIRMAN OF THE BOARD PRESIDENT DIRECTOR ASSOCIATE DIRECTOR

UNITED STATES DEPARTMENT OF COMMERCE National Oceanic and Atmoapharia Adminiswation NATIONAL MARINE FISHERIES SERVICE

Miami Laboratory Southeast F i s h e r i e s Center 75 Virg in ia Beach Drive ' Miami, F lo r ida 33149

Ju ly 30, 1987

Dr. J e f f r e y Lincer S c i e n t i f i c Advisor Ringling MacArthur Reserve County of Sarasota 1487 Second S t r e e t , S u i t e D Sa raso ta , FL 33577

Dear D r . Lincer:

Enclosed is t h e r e p o r t , "An Ecosystem View of Management Research in t h e Myakka River", prepared f o r t h e County of Sarasota under Account Number #30260-406-118005-537313. A d r a f t copy of t h i s r epor t was reviewed by D r . Ernes t Estevez m d his suggest ions and comments were taken i n t o account in p repa ra t ion of t h e f i n a l version. An invoice fo r $7,000.00 w i l l be sent to you from our admin i s t r a t ive o f f i c e s under sepa ra t e cover.

S ince re ly ,

Joan A. Browder, Ph.D. Research Ecologis t