Species Profiles: Life Histories and Environmental ...aquaticcommons.org/3579/1/1986_stan.pdfoccurs from the Gulf of St. Lawrence, Canada, to Key Bi scayne, Florida. This species was

REFER.ENCE COPY Do Not Remove from the Library

U. S. Fish and Wildlife Service National Wetlands Research Center - -

Biological Report 82 (1 1.64) /00 Cajun Dome Boulevard TR EL-82-4 JUIY 1986 Lafoyette, Louisiana 70506

Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Gulf of Mexico)

AMERICAN OYSTER

Coastal Ecoloav G r o u ~ Fish and Wildlife Service Waterways ~ x ~ e r i m e n i station U.S. Department of the Interior U.S. Army Corps of Engineers

B i o l o g i c a l Report aZ(11.64) TR EL-82-4 J u l y 1986

Species P r o f i l e : L i f e H i s t o r i e s and Environmental Requirements o f Coastal Fishes and Inve r teb ra tes (Gu l f of Mexico)

AMERICAN OYSTER

Jon G. Stanley Mai ne Cooperat ive F ishery Research U n i t

313 Murray Hal 1 U n i v e r s i t y o f Mai ne Orono, ME 04469

and

Mark A. S e l l e r s Program i n Oceanography

U n i v e r s i t y o f Maine a t Orono I r a C. D a r l i n g Center Walpole, ME 04573

P r o j e c t Manager C a r r o l l Cordes P ro jec t O f f i c e r

David Moran Nat iona l Wetlands Research Center U.S. F i sh and W i l d l i f e Serv ice

1010 Gause Boulevard Sl i d e l 1 , LA 70458

Performed f o r Coastal Ecology Group

Waterways Experiment S t a t i o n U. S. Army Corps o f Engineers

Vicksburg, MS 39180

and

Nat iona l Wetlands Research Center Research and Development F i s h and W i l d l i f e Serv ice

U. S. Department of t h e I n t e r i o r Washi ngton, DC 20240

This se r i es should be referenced as fo l lows:

U.S. F i s h and W i l d l i f e Service. 1983-19 . Species p r o f i l e s : l i f e h i s t o r i e s and environmental requirements o f c o a s t s f i shes and inver tebra tes . U. S. F i sh W i l d l . Serv. B i o l . Rep. 82(11). U.S. Army Corps o f Engineers, TR EL-82-4.

Th is p r o f i l e should be c i t e d as fo l lows:

Stanley, J.G., and M.A. Se l l e rs . 1986. Species p r o f i l e s : l i f e h i s t o r i e s and environmental requirements o f coasta l f i shes and i nve r teb ra tes (Gul f o f Mexico)--American oys ter . U.S. F i s h Wi ld l . Serv. B i o l . Rep. 82(11.64). U.S. Army Corps o f Engineers, TR EL-82-4. 25 pp.

PREFACE

Th is species p r o f i l e i s one o f a se r i es on coasta l aquat ic organisms, p r i n c i p a l l y f i s h , o f spor t , commercial, o r eco log i ca l importance. 'The p r o f i l e s a re designed t o p rov ide coasta l managers, engineers, and b i o l o g i s t s w i t h a b r i e f comprehensi ve sketch o f t h e b i o l o g i c a l c h a r a c t e r i s t i c s and environmental requirements o f t h e species and t o descr ibe how popu la t ions o f t he species may be expected t o r e a c t t o environmental changes caused by coasta l development. Each p r o f i l e has sec t ions on taxonomy, 1 i f e h i s t o r y , eco log i ca l r o l e , environmental requ i rements , and economic importance, i f appl i cab le . A t h r e e - r i ng b inde r i s used f o r t h i s s e r i e s so t h a t new p r o f i l e s can be added as they are prepared. Th i s p r o j e c t i s j o i n t l y planned and f inanced by the U. S. Army Corps o f Engineers and t h e U.S. F i s h and W i l d l i f e Service.

Suggestions o r questions regard ing t h i s r e p o r t should be d i r e c t e d t o one of t he f o l l owing addresses.

I n fo rma t ion Trans fer Special i s t Nat iona l Wetlands Research Center U.S. F i s h and W i l d l i f e Serv ice NASA-Sl i d e l l Computer Compl ex 1010 Gause Boulevard S l i d e l l , LA 70458

U.S. A r m y Engineer Waterways Experiment S t a t i o n At ten t ion : WESER-C Post O f f i c e Box 631 Vicksburg, MS 39180

CONVERSION TABLE

M e t r i c t o U.S. Customary

Hul t i p l y

m i l 1 i m e t e r s (mn) c e n t i m e t e r s (on) m e t e r s (m) k i 1 m e t e r s ( km)

2 square mete rs (m ) 10.76 square k i 1 m e t e r s ( km2) 0.3861 h e c t a r e s (ha) 2.471

l i t e r s ( 1 ) c u b i c n e t e r s (m3) c u b i c meters

To O b t a i n

i nches inches f e e t m i l es

square f e e t square ! n i l es acres

ga l 1 ons c u b i c f e e t acre- f e e t

m i l 1 ig rams (mg) 0.00003527 ounces grams ( g ) 0.03527 ounces k i l o g r a m s ( k ) 2.205 pounds m e t r i c tons f t ) 2205.0 pounds m e t r i c t o n s 1.102 s h o r t t o n s k i 1 oca l o r i e s ( k c a l ) 3.968 B r i t i s h thennal u n i t s

Cel s i u s degrees 1.8(Oc) + 32 Fahrenhe i t degrees

U.S. Customary t o M e t r i c

i nches 25.40 inches 2.54 f e e t ( f t ) 0.3048 fathoms 1.829 m i l e s ( m i ) 1.609 n a u t i c a l m i l e s ( m i ) 1.852

square f e e t ( f t 2 ) acres 2 square m i l e s (mi )

g a l l o n s ( g a l ) c u b i c f e e t ( f t 3 ) acre- f e e t

ounces (02 ) 28.35 pounds ( l b ) 0.4536 s h o r t t o n s ( t o n ) 0.9072 B r i t i s h thermal u n i t s ( B t u ) 0.2520

m i l 1 i m e t e r s c e n t i m e t e r s ineters meters k i l orneters k i 1 oqe te rs

square meters hec ta res square k i l o m e t e r s

1 i t e r s c u b i c meters cub ic meters

grains k i 1 ograTs m e t r i c tons k i 1 oca l o r i e s

Fahrenhe i t degrees 0.5556(OF - 32) C e l s i u s degrees

CONTENTS

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CONVERSIONTABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . NONMENCLATLlRE/TAXONOMY/RANGE . . . MORPHOLOGY/ IDENTIFICATION AIDS . . . REASON FOR INCLUSION I N SERIES . . . . . . . . . . . . LIFE HISTORY . . . . . . . . . . . . . Spawning . . . . . . . . . . . . . . Larvae J u v e n i l e s . . . . . . . . . . . . . Adu 1 t s . . . . . . . . . . . . . .

GROWTH CHARACTERISTICS . . . . . . . . . . . . . COMMERCIAL SHELLFISHERIES Popu 1 a t i on Dynarni cs . . . . . . . . . . . . . . . . . . . ECOLOGICAL ROLE . . . . . ENVIRONMENTAL REQUIREMENTS Ternperatu r e . . . . . . . . . . . . S a l i n i t y . . . . . . . . . . . . . Subs t ra te . . . . . . . . . . . . . Cur ren t . . . . . . . . . . . . . . 0 xy gen . . . . . . . . . . . . . . Suspended Sol i d s and Sed imenta t ion Other Env i ronmenta l Requ i rements .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . LITERATURE CITED

Page

ii i i v v i

1 1 3 3 3 4 5 5 6 6 9

10 12 12 13 14 14 14 15 15

ACKNOWLEDGMENTS

We thank Herber t Hidu, P ro fesso r of Zoology, U n i v e r s i t y o f Maine; Mark S. Van Hoose, B i o l o g i s t 11, Alabama Department o f Conserva t ion and N a t u r a l Resources ; Edwin W . Cake, Jr . , Head, O y s t e r B i o l o g y Sec t ion , G u l f Coast Research Labora to ry ; Mark Chantry, Mar ine B i o l o g i c a l Laboratory , Lou i s i ana Department o f W i l d l i f e and F i s h e r i e s ; and Dex te r S. Haven, V i r g i n i a I n s t i t u t e o f Mar ine Science f o r r ev i ew ing t h e manuscr ip t and o f f e r i n g many h e l p f u l suggest ions.

Figure 1. American oys te r from s o f t sub- s t r a t e w i t h j u v e n i l e attached (Gal t s o f f 1964).

AMERICAN OYSTER

S c i e n t i f i c name . . . . . Crassostrea

. . . American oys te r (F igure 1)

Other common name . . . Eastern oyster Class . . . . . B i v a l v i a (Pelecypoda) Order . . . . . .Mytoloida (Pteroidea) Fami ly. . . . . . . . . . . Ost re i dae

Geographic range: The American oys te r l i v e s i n es tua r ies and behind b a r r i e r i s l ands ; it i s abundant a long t h e g u l f coas t from F l o r i d a t o Texas (F igure 2). The Gu l f o f Mexico has about 3600 km2 (1400 m i 2 ) o f h a b i t a t s u i tab1 e f o r t he American oys te r ( B u t l e r 1954). I t s range extends t o t he Yucatan Peninsula o f Mexico and t o Venezuela. Along the eas t coast o f Nor th America, i t occurs from t h e Gu l f o f St. Lawrence, Canada, t o Key B i scayne, F lo r i da . Th is species was int roduced w i t h 1 i m i t e d success t o Japan, A u s t r a l i a , Great B r i t a i n , Hawaii, and t h e west coast o f Nor th

America, b u t i t has no t become abundant (Ahmed 1975). The American oys te r i s most abundant i n t h e Gu l f of Mexico, Chesapeake Bay, and Long I s l a n d Sound.

MORPHOLOGY/IDENTIFICATION AIDS

The l e f t va lve i s almost always t h i c k e r and heav ier than t h e r i g h t , and more deeply cupped (Yonge 1960; G a l t s o f f 1964) . The o y s t e r i s ce- mented t o t h e subs t ra te on i t s l e f t valve. Hinge tee th a re absent, but a bu t t ress on t h e r i g h t valve f i t s i n t o a depression on t h e l e f t . There i s no gap between t h e valves when f u l l y c l osed .

She l l shape i s var iab le . On hard bottoms, beaks (umbones) u s u a l l y a re curved and p o i n t toward t h e p o s t e r i o r , whereas i n s i l t y environments o r on reefs, umbones a re u s u a l l y s t r a i g h t . S o l i t a r y oysters f rom hard subst ra tes are rounded and ornamented w i t h r a d i a l r idges and f o l i a t e d processes, whereas

those f r om s o f t subs t ra tes o r r e e f s a re more s l ende r and spa rse l y o r - namented. She1 1 t h i ckness a l s o depends on env i ronment. Oysters on hard subs t ra tes have t h i c k e r and l ess f r a - g i l e s h e l l s t han those on s o f t sub- s t r a t e s . The " index o f shape" ( ( he igh t + w id th ) / l eng th ) v a r i e s f rom 0.5 t o 1 .3 i n sou thern popu la t i ons and from 0.6 t o 1.2 i n no r t he rn popul a t i ons.

The s h e l l grows a l ong a d o r s a l - v e n t r a l ax i s , bu t t h e ang le o f t h e a x i s i s n o t permanent and may change seve ra l t imes over t h e l i f e s p a n o f an i n d i v i d u a l , r e s u l t i n g i n a z igzag p a t t e r n . The growth a x i s may change as much as 90". The s h e l l o f oys te rs 3- t o 5-years o l d i s u s u a l l y 10 t o 15 cm l o n g . A l t h o u g h t i s s u e mass reaches an upper l i m i t , t h e s h e l l con t inues t o grow over t h e l i f e s p a n of an o y s t e r (S tenze l 1971). Throughout t h i s r e v i e w s h e l l h e i g h t i s t e r m e d 1 ength .

The American o y s t e r i s monomya- r i a n ( a n t e r i o r adductor muscle has been l o s t ) . The i n t e r i o r o f t h e s h e l l has a purp le-p igmented adductor nusc le sca r s i t u a t e d s l i g h t l y p o s t e r i o r and ven t ra l . A second muscle scar, o f t h e Quens ted t ' s muscle, i s s i t u a t e d v e n t r a l t o and a s h o r t d i s t a n c e f r o m t h e h inge. The p u r p l e p i gmen ta t i on on t h e adductor muscle sca r d i s t i n g u i s h e s t h e American o y s t e r f rom s i m i l a r species. I n t h e mangrove o y s t e r (C. r h i z o horae) and P a c i f i c o y s t e r (c.

t h e muscle sca r i s l i g h t i y * pigmented and i n C. r i v u l a r i s i t i s u np i gment ed . The s h e l l o f t h e mangrove o y s t e r i s l e s s p l i c a t e d t han t h a t o f t h e American oys te r . There a re no o t h e r species o f Crassos t rea sympat r i c w i t h t h e American oys te r i n t h e M i d - A t l a n t i c reg ion. Species o f Crassos t rea a re d i s t i n g u i s h a b l e f rom species o f Os t rea by t h e promyal chamber, which i s w e l l developed i n Crassost rea species, b u t n o t i n Ds t rea . By t r a p p i n g s a l t w a t e r , t h i s chamber may a l l o w t h e American o y s t e r t o t o l e r a t e w ide r f l u c t u a t i o n s i n s a l i n i t y i n es tua r i es .

Crassos t rea species a r e ov iparous (gametes a r e re leased i n t o t h e wate r ) , whereas Ostrea species i ncuba te f e r t i - l i z e d eggs i n t h e mant le c a v i t y . The morpho logy o f l a r v a l s t a g e s i s de- s c r i b e d by K i l g e n and Dugas (1984). Advanced Crassos t rea l a r v a e a r e d i s t i n g u i s h e d from t h e l a r v a e of o t h e r b i va l ves by l eng th -w id th measurements, and an asymmetric umbo. The morpho logy o f t h e d e n t i t i o n on t h e h inge d i s t i n g u i s h e s t h e l a r v a e o f t h e Ameri can o y s t e r f rom o t h e r b i va l ves (Lu t z e t a l . 1982).

REASON FOR INCLUSION I N SERIES

The American o y s t e r suppor ts an impo r tan t comnerci a1 f i s h e r y f r om t h e Gu l f o f Mexico t o t h e Gu l f o f St . Law- rence, and i s an impo r tan t m a r i c u l t u r e species. More oys te r s a re processed t han any o t h e r s i n g l e f i s h e r y p roduc t i n t h e U n i t e d S ta tes , and over 10,000 people work i n t h e o y s t e r i ndus t r y . Oysters a r e va lued as a l u x u r y f ood i t e m and a re t h e keystone species o f a reef b iocoenosis t h a t i nc l udes seve ra l hundred species (Wel l s 1961). Because oys te rs i n h a b i t es tua r i es , t hey a r e p a r t i c u l a r l y vu l ne rab le t o urban and i n d u s t r i a l d is tu rbances (Cake 1983).

LIFE HISTORY

Spawni nq

Gametogenesis and spawning a r e s t i m u l a t e d by changes i n water temperature (Hopkins e t a l . 1954; Kaufman 1978; Andrews 1979). Spawning tempera tu re d i f f e r s among popu la t i ons . Based on spawning temperatures, Stau- ber (1950) recognized t h r e e phys io l og - i c a l races: one f rom t h e G u l f o f Mexico t h a t spawns when wate r temperatures a r e near 25 OC, and two f rom t h e e a s t coas t t h a t spawn a t 16 OC and 20 OC. I n t h e G u l f o f Mexico, t h e temperature must be c o n s t a n t l y above 20 OC f o r spawning, and above 25 OC f o r mass spawnings (Schlesselman 1955). I n t h e

Apa lach i co la R i v e r es tua ry , F l o r i d a , t h e o y s t e r does n o t spawn u n t i l water temperature reaches 22.5 O C and mass spawning occurs a t 26 O C ( I n g l e 1951).

The American o y s t e r i n t h e no r t he rn G u l f o f Mexico spawns from March th rough November accord i ng t o B u t l e r (1954) and f r o m A p r i l t o October accord ing t o Hayes and Menzel(1981). I n Lou is iana , spawning peaks occur i n l a t e May, e a r l y June, and September ( P o l l a r d 1973). I n M i s s i s s i p p i , most oys te r s spawn f r om May t o October and spawning i n t e n s i t y i s g rea tes t i n June (MacKenzie 1977). I n Galveston Bay, Texas, spawning begins i n e a r l y A p r i l about t h e t i m e water temperatures exceed 20 O C and con t inues a t l e a s t u n t i l t h e end of August (Hopki ns 1931). Spat s e t t i n g i n d i c a t e s t h a t t h e American o y s t e r p robab l y spawns i n a l l months i n sha l low warm bays i n Texas (e.g. , Red f i sh Bay) w i t h t h e excep t i on o f J u l y and August (Copeland and Hoese 1966). Water temperatures exceeding 35 O C i n those months may l i m i t t h e e x t e n t o f spawning.

Spawning does n o t depend d i r e c t l y on t i d a l c y c l e s (Loosanof f and Nomejko 1951), b u t sun1 i g h t may warm t h e water d u r i n g low t i d e and s t i n u l a t e spawning (Dr innan and S t a l l w o r t h y 1979).

The t i m i n g and i n t e n s i t y o f spawning i s i n i t i a t e d by males t h a t r e l ease t h e i r sperm and a pheromone i n t o t h e w a t e r . The f e m a l e s spawn when sperm e n t e r t h e i r water t r a n s p o r t system (Andrews 1979), o r when pheromone s t i m u l a t e s females t o r e l ease t h e i r eggs i n a mass spawning (Bahr and L a n i e r 1981). Each female produces 23 m i l 1 i o n t o 86 m i l l i o n eggs pe r spawning; t h e number i s propor- t i o n a l t o t h e s i z e of t h e i n d i v i d u a l (Davis and Chanley 1955). Egg counts o f 15 m i l l i o n t o 115 m i l l i o n were c i t e d by Yonge (1960). Females may spawn seve ra l t imes i n one season ( D a v i s and Chan ley 1955 ) . The egg h a t c h e s 6 h a f t e r f e r t i l i z a t i o n a t water temperatures near 24 O C

(Loosanof f 1965a).

Larvae

Oys te r l a r v a e a r e meropl ank ton i c and remain i n t h e wate r column f o r 2 t o 3 weeks a f t e r h a t c h i n g (Bahr and L a n i e r 1981). Du r i ng t h i s p e r i o d t h e l a r v a e pass through seve ra l s tages o f development ( C a r r i k e r and Palmer 1979; K i l g e n and Dugas 1 9 8 4 ) . A f t e r t h e b l a s t u l a (3.2 h ) , g a s t r u l a (4.5 h ) , and t rochophore (10 h ) s tages ( P a r r i s h 1969), t h e l a r v a e sec re te a s t r a i g h t - h i n g e s h e l l and d e v e l o p a r i n g o f locomotory c i l i a c a l l e d t h e velum. Th is s t r a i ght -h inge l a r v a o r p rod i sso - conch I i s about 75 Dm i n d iameter . I t develops i n t o a prodissoconch I 1 l a r v a ( a l s o termed an eyed l a r v a o r pedi ve l i g e r ) , which i s c h a r a c t e r i z e d by a pronounced umbone. T h i s l a r v a i s a v igorous swimmer, and has a p a i r of pigmented eyes and an e l onga te f o o t w i t h a l a r g e b y s s a l g l a n d (Andrews 1979). Mean d iameter o f prodissoconch I 1 l a r v a e i s 0.3 mm.

Young l a r v a e (prodissoconch I ) i n L i t t l e Egg Harbor, New Jersey, s t a y i n t h e wate r column about 1 m below t h e s u r f a c e ( C a r r i k e r 1951). O lder l a r v a e (prodissoconch I I ) a re near t h e bot tom o f t h e es tua r i es d u r i n g f l o o d t i d e and r i s e nearer t h e sur face d u r i n g t h e ebb t i d e . Andrews (1979) ques t ioned t hese f i n d i n g s because i n t h e l abo ra to r y , o l d e r l a r v a e a re s t i m u l a t e d t o swim by inc reased s a l i n i t i e s and i n h i b i t e d by decreased s a l i n i t i e s (Haskin 1964). Swimming v e l o c i t y inc reased t h r e e f o l d when s a l i n i t y was inc reased 0.5 pp t / h (Hidu and Haskin 1978). Upward swimming i s n e a r l y 1 cm/sec (Andrews 1979). These behav io ra l t r a i t s may r e s u l t i n s e l e c t i v e t i d a l t r a n s p o r t so t h a t l a r v a e p o s i t i o n themselves i n t h e estuary. Genera l ly , l a r v a e a r e t r a n s p o r t e d toward t h e head o f an es tua ry aga ins t a n e t downstream f l ow ( S e l i g e r e t a l . 1982), presumably because t hey use t hese behav io ra l responses. Cur ren ts c a r r y l a r v a e cons iderab le d is tances : 6.5 km i n A l l i g a t o r Harbor, F l o r i d a (Marshal 1 1954), and 10 km i n Lou i s i ana (Gunter

1951). Oys te r l a r v a e d r i f t westward a l ong t h e coas t of t h e Gulf of Mexico (Bu roke r 1983).

Ju veni 1 es

Two t o t h r e e weeks a f t e r ha tch ing , o y s t e r l a r v a e commence a p e r i o d o f c r a w l i n g i n a c i r c u l a r p g t e r n , presumably seek ing a s o l i d s u r f a c e f o r attachment (Andrews 1979). I n Long I s l a n d Sound t h e f i r s t s e t i s 18 days a f t e r t h e f i r s t spawning (Loosanof f and Nomejko 1951). I n Galveston Bay, Texas, s e t t i n g was f i r s t seen 2 months a f t e r spawn ing when t h e l a r v a e were about 0.2 mm l o n g (Hopk i ns 1931). A f t e r at tachment w i t h a d r o p l e t o f 1 i q u i d cement exuded f r om a p o r e i n t h e f o o t , t h e y l o s e t h e velum and f o o t and a r e c a l l e d spa t ( s p a t a re newly s e t t l e d oys te r s ) . She1 1s a r e p r e f e r r e d as attachment s i t e s . bu t s tones and o t h e r f i r m sur faces may be used. Spat t h a t s e t d u r i u g t h e f i r s t 3 days a f t e r metamor- phos is may grow f a s t e r t han those s e t - t i ng l a t e r (Losee 1979). Metamorpho- s i s may be delayed i f s u i t a b l e sub- s t r a t e i s n o t l o c a t e d (Newkirk e t a l . 1977). Burke (1983) d e f i n e d s e t t l e - ment as t h e behav io r o f d ropp ing t o t h e bottom, i n c o n t r a s t t o metamorpho- s i s , which i s t h e i r r e v e r s i b l e deve l - opmental process.

Severa l f a c t o r s i n f l u e n c e t h e s e t t i n g behav io r of la rvae . Hidu and Haskin (1971) be1 i eved t h a t r i s i n g water temperatures over t i d a l f l a t s d u r i n g f l o o d t i d e s s t i m u l a t e s e t t i n g . I n t h e l abo ra to r y , r i s i n g temperatures t r i g g e r s e t t i n g ( L u t z e t a l . 1970). Swimming l a r v a e have p o s i t i v e pho to - t a x i s , which becomes nega t i ve w i t h an i nc rease i n tempera tu re (Bahr and L a n i e r 1981). L i g h t i n h i b i t s s e t t i n g i n tanks (Shaw e t a l . 1970), and oys te r s p r e f e r t o s e t on t h e under- s ides o f s h e l l s ( R i t c h i e and Menzel 1 9 6 9 ) . More o y s t e r s s e t t l e i n t h e s u b t i d a l zone t han elsewhere i n Delaware Bay (Hidu 1978). I n sha l l owe r water, se t t l emen t i s g r e a t e s t on a r t i f i c i a l s u b s t r a t e h e l d

away f rom t h e bot tom because s i 1 t a t i on i n h i b i t s s e t t i n g (Andrews 1979).

Oys te r l a r v a e s e t i n e s t a b l i s h e d o y s t e r beds and i n o t h e r h a b i t a t s w i t h f i r m s u b s t r a t e and s u i t a b l e s a l i n i - t i e s . C r i s p (1967) p o s t u l a t e d t h a t l a r v a e a re a t t r a c t e d t o t h e p r o t e i n a - ceous su r f ace of t h e p e r i o s t racum o f a d u l t she1 1s and observed t h a t l a r v a e d i d n o t s e t t l e on s h e l l s t h a t had been t r e a t e d w i t h bleach. Hidu (1969) dem- ons t ra ted , however, t h a t a water-borne f ac to r , perhaps a pheromone, s t i r m - l a t e s l a r v a e t o s e t t l e on o y s t e r s h e l l s . Cur ren ts a l s o i n f l u e n c e s e t - t i n g p a t t e r n s : se t t l emen ts i n Delaware Bay a r e heav ies t where t i d a l c u r r e n t s c u t th rough s a l t marshes (Keck e t a l . 1973 ) . J u v e n i l e s 26 t o 75 mm i n h e i g h t and 7 t o 1 4 months o l d a r e des igna ted as seed oys te r s (Chat ry e t a l . 1983).

Adu 1 t

Because a d u l t oys te r s a r e s e s s i l e , t h e i r d i s t r i b u t i o n depends on where t h e l a r v a e s e t and on subsequent s u r v i v a l o f t h e spat . Oysters t y p i - c a l l y l i v e i n clumps c a l l e d r e e f s o r beds, i n which t h e y a r e t h e dominant organism. The mass o f s h e l l s some- t imes a1 t e r s c u r r e n t s and inc reases d e p o s i t i o n o f p a r t i c u l a t e s s o t h a t t h e l o c a l env i ronment i s mod i f ied .

A d u l t s a r e d ioec ious , b u t o f t e n change gender, e x h i b i t i n g protandrous hermaphrodi t ism (Bahr and L a n i e r 1981). The gender and t h e process o f sex i n v e r s i o n a r e g e n e t i c a l l y determined by perhaps t h r e e l o c i ( H a l e y 1 9 7 7 ) . T y p i c a l l y t h e young a d u l t s a r e p redominan t l y ma1 es ; subsequent sex i n v e r s i o n w i t h age i n - creases t h e number o f females. Sex r a t i o s i n t h e James R i v e r E s t u a r y , V i r 'g in ia , change from 90% males a t 1 y e a r o f age t o 80% females i n o l d e r oys te r s (Andrews 1979). I n Lou is iana , 76% of oys te r s were males i f a t tached t o o l d e r oys te r s and 46% were males i f a t tached t o dead s h e l l s (Menzel 1951). Oysters may become s e x u a l l y mature i n

t h e Gul f o f Mexico 4 weeks a f t e r a t tachment (Menzel 1951). Those oys te r s t h a t mature d u r i n g t h e f i r s t summer o f l i f e , however, do n o t c o n t r i b u t e s i g n i f i c a n t l y t o t h e y e a r c l ass because o f t h e r e l a t i v e l y low number of eggs t h a t t hey produce (Hayes and Menzel 1981).

GROWTH CHARACTERISTICS

American oys te rs grow f a s t e s t d u r i n g t h e i r f i r s t 3 months o f l i f e ( B a h r 1976) . B u t l e r ( 1 9 5 4 ) s t a t e d t h a t oys te r s i n t h e gu l f r eg ion grow abou t 50 mmlyear . I n A p a l a c h i c o l a Bay, F l o r i d a , oys te r s reach 25 mm i n 5 weeks, and 100 mn i n 31 weeks ( I n g l e 1950 ) . I n a second s t u d y , o y s t e r s were 4 mm a t 1 week o f age, 8 mm a t 2 weeks o f age, and 27 mm a t 5 weeks o f age ( I n g l e and Dawson 1952 ) . F o r comparison, oys te r s i n Pensacola Bay, F l o r i d a , r a r e l y exceed 75 mm o f growth i n t h e i r f i r s t y e a r ( B u t l e r 1954). I n Lou is iana , oys te r s grew a t t h e r a t e of 0.26 t o 0.30 mm p e r day d u r i n g t h e f i r s t growing season (Gunter 1951). Oysters i n Lou i s i ana u s u a l l y reach 30 mm i n l e n g t h i n 3 months, 55 t o 60 mm i n 1 year , 85 t o 95 mm i n 2 years, and 105 t o 115 mm i n 3 y e a r s ( M a c k i n 1961a). There i s v a r i a t i o n i n growth r a t e i n Lou is iana : t h e t i m e t o reach 70 mn was 45 weeks a t Grand Pass, 25 weeks i n u p p e r B a s t i a n Bay, and 1 2 weeks i n lower B a s t i a n Bay (Owen 1953a). Instantaneous month ly growth c o e f f i c i e n t s ranged f r om 0.42 t o 0.84 (Gi 11 mor 1982).

Growth i s i n f l u e n c e d by tempera- t u r e , s a l i n i t y , i n t e r t i d a l exposure, t u r b i d i t y , and food. Growth i s g rea t - e s t i n August and September a f t e r spawning, when glycogen reserves a r e r e s t o r e d (Loosanof f and Nomejko 1949; P r i c e e t a l . 1975 ) . G row th i n t h e g u l f r e g i o n i s cont inuous th roughout much o f t h e y e a r , t h o u g h i t may be i n t e r r u p t e d by unusual c o l d pe r i ods o r by spawning. Growth i s s low d u r i n g spawning because most o f t h e energy i s used f o r gamete p r o d u c t i o n i n s t e a d of add ing body biomass. I n Lou is iana ,

t h e glycogen con ten t o f oys te r s dec l i nes t o suppor t gonad ma tu ra t i on i n A p r i l and reaches l o w e s t l e v e l s d u r i n g spawning i n May, June, and J u l y (Hopkins e t a l . 1954). B u t l e r (1953) n o t e d an i n c r e a s e i n b iomass a f t e r spawning w i t h o u t an i nc rease i n s h e l l l eng th . Oysters expend as much as 48% o f t h e i r annual energy budget i n r ep roduc t i on (Dame 1976).

Growth o f oys te r s depends on env i ronmental c o n d i t i o n s and t h e i r p o s i t i o n and d e n s i t y i n t h e o y s t e r r e e f . F l u c t u a t i n g environments may promote b e t t e r growth. F o r example, oys te rs i n f l u c t u a t i n g s a l i n i t y w i t h i n normal ranges tend t o grow b e t t e r t h a n oys te r s under a r e l a t i v e l y cons tan t s a l i n i t y ( P i e r c e and Conover 1954). Oysters exposed f o r s h o r t pe r i ods d u r i n g t h e t i d a l c y c l e grow about t h e same r a t e as those con t i nuous l y sub- merged (Gi l l m o r 1982). Long exposure ou t o f water, however, reduces growth. Oysters i n r ee f s exposed about 20% o f t h e t i m e may grow about t w i c e as f a s t as those exposed 60% o f t h e t ime. The growth r a t e o f t h e o y s t e r i s d i r e c t l y r e l a t e d t o phy top lank ton dens i t y . Oysters grow f a s t e r i n n u t r i e n t - r i c h s a l t ponds than i n t i d a l creeks where p r ima ry p r o d u c t i v i t y i s lower (Manzi e t a l . 1977). I n d i v i d u a l s i n popu la t i ons o f oys te r s o f h i g h d e n s i t y grow s lower than those a t low d e n s i t y (Copeland and Hoese 1966). Crowding, however, may p reven t spawning and thus i nd i r e c t l y 1 ead t o inc reased growth ( B u t l e r 1953).

A Wal fo rd p l o t p r e d i c t s t h a t oys te r s i n South C a r o l i n a would cease growing when 140-mn l o n g (Dame 1971); however, oys te r s 200-mm l o n g occur.

COMMERCIAL SHELLFISHERIES

The Amer i can o y s t e r has t r a d i - t i o n a l l y suppor ted a va luab le s h e l l f i s h e r y a l ong t h e e n t i r e gu l f coast . The s h e l l f i s h e r i e s a r e concent ra ted i n bays and e s t u a r i e s ( F i g u r e 2). The l and ings i n t h e Gu l f S ta tes combined average about 8,000

m e t r i c tons (18 m i l l i o n pounds) annua l l y (Table 1 ) . Oys te r p r o d u c t i o n has been r e l a t i v e l y s t a b l e ; t h e land ings s i n c e 1950 have va r i ed on l y f r om 10 m i l l i o n t o 27 m i l l i o n pounds. The land ings o f oys te r s i n t h e Gu l f o f Mexico a re about a t h i r d o f t h e U.S. 1 andi ngs . The land ings f o r t h e i n d i v i d u i r l S ta tes vary by an o rde r o f magnitude (Table 2 ) . Lou is iana has t h e l a r g e s t she1 l f i s h e r i e s f o r

oys te rs ; annual land ings a r e about 9 m i l l i o n pounds (4,000 m e t r i c t o n s ) . The wes t c o a s t o f F l o r i d a has t h e second l a r g e s t f i s h e r y , about h a l f t h a t o f Lou is iana . Poor y e a r c lasses l ead t o reduced harves ts . Lou i s i ana had poor ha rves t s i n 1979, 1980, and 1981; F l o r i d a i n 1973 th rough 1976; and Texas i n 1974, 1975, 1978, 1979 and 1981. Alabama and M i s s i s s i p p i have t h e same t r e n d s as L o u i s i a n a .

T a b l e 1. O y s t e r l a n d i n g s ( t h o u s a n d s o f pounds ; meat w e i g h t ) by geographic r eg ion f o r t h e years 1950-1982. (From U.S. Dep. Commer., N a t l . Mar., F i sh . Serv., NOAA, N a t l . F ish . S t a t . Program. Annual summaries o f o y s t e r land ings .)

South G u l f o f Year New England M i d - A t l a n t i c Chesapeake Atlantic Mexico

Table 2. Oyster landings (thousands o f pounds; meat weight) for the Gulf S t a t e s , 1930-82 (From U.S. Dep. Commer., Nat. Mar. F ish. Serv . , NOAA, N a t l . F ish. S t a t . Program. Summation of annual repor ts . )

Years ~ l o r i d a ~ Alabama Miss iss ipp i Louisiana Texas T o t a l

1930 1,501 1931 1,406 1932 1,109 1934 1,357 1936 917 1937 817 1938 858 1939 742 1940 669 1945 1,496 1950 873 1951 681 1952 542 1953 564 1954 668 1955 6 30 1956 856 1957 710 1958 795 1959 1,415 1960 1,931 196 1 3,255 1962 4,592 1963 4,282 1964 2,793 1965 3,789 1966 4,157 1967 4,578 1968 5,317 1969 4,912 1970 3,573 1971 3,529 1972 3,231 1973 2,409 1974 2,653 1975 2,134 1976 2,602 1977 4,072 1978 5,780 1979 6,048 1980 6,445 1981 7,179 1982 4,833

a ~ u l f coast only.

Oysters are taken by handpick ing o f clumps f rom reefs (Bahr and Lan ier 1981), hand and pa ten t tonging, and dragging and dredging (Kor r inga 1976). I n Louisiana, oys ters are taken most ly w i t h dredges (Pausina 1971). Tonging i s 1 i m i t e d t o water 4-m deep o r less ; dredging requ i res a l a r g e r vessel (Maghan 1967). I n M iss i ss ipp i coasta l waters, t he method used depends on t h e type o f f i s h e r y . I n t h e M iss i ss ipp i Sound near Bay S t . L o u i s and Pass C h r i s t i a n , oysters are taken by dredging o r w i th tongs; i n B i l o x i Bay and Gravel ine Bayou they are dredged f o r t r a n s p l a n t a t i o n t o grow out s i t e s ; and near Horn I s l a n d they are taken by hand f o r f o o d and r e c r e a t i o n (Og le 1979). I n Alabama, tong ing and handpick ing are t h e only l e g a l means of t a k i n g oysters; t h i s i s because t h e m a j o r r e e f s a r e c l o s e t o s h o r e i n s h a l l o w wa te rs (Mark S . Van Hoose, A1 abama Department o f Conservation and Natura l Resources, pers. comm.) . Power equipment has made capture more e f f i c i e n t but i t a l so increases t h e p o t e n t i a l f o r dep le t i ng t h e beds.

The American oys ter i s t h e dominant species i n mar i cu l t u re i n t h e Uni ted States. I n 1980, t h e y i e l d o f oysters i n m a r i c u l t u r e was 10,753 m e t r i c tons (about 24 m i l l i o n l b ) valued a t $37 m i l l i o n , which was about 55% o f t h e t o t a l U.S. s h e l l f i s h e r y harves t (19,250 m e t r i c tons; 42.4 m i 11 i o n 1 b) . The equi valences between d i f f e r e n t values repor ted f o r harvest are: 1 bu = 35 1 = 32 kg t o t a l weight = 7.8 p i n t s o f meats = 3.4 k g meat weight (Pruder 1975).

The market q u a l i t y o f t h e meat var ies w i t h t h e season. The y i e l d o f oys ter meat per s h e l l i s h ighest i n March before reproduct ion and lowest i n t h e summer i n Texas (Gunter 1942) and F l o r i d a (Rockwood and Mazek 1977). The reduced y i e l d s du r ing spawning per iods correspond t o a reduced cond i t i on index f o l l o w i n g spawning (Hopk ins e t a l . 1954; Lawrence and Sco t t 1982 ) .

Even ' w i l d ' oys ters are o f t e n c u l t i v a t e d by a l t e r i n g t h e substrate. Oyster s h e l l s ( cu l t ch ) p laced i n s u i t a b l e h a b i t a t l a c k i n g subst ra te promote se t t lement o f t h e l a rvae (Whi t f i e l d and Beaumariage 1977). Su i tab le h a b i t a t can be c reated by redepos i t i ng bu r ied she1 1 s on the sur face (May 1976) b u t on l y i f t h e bottom i s r e l a t i v e l y hard a t t h e s i t e o f depos i t i on (Eckmayer 1977). Dredging i s e f f e c t i v e i n r e h a b i l i - t a t i n g oys te r r e e f s i f the bottom i s re1 a t i v e l y hard (Eckmayer 1977).

Populat ion Dynamics

A vast m a j o r i t y o f t h e eggs and 1 arvae produced by Ameri can oysters pe r i sh before s e t t i n g . Fo l l ow ing spawning, oys te r l a r vae are abundant p lank ters , ranging from 2.0 t o 5.5 per 1 i t e r i n V i r g i n i a coasta l waters (Andrews 1979; S e l i g e r e t a l . 1982). I n t h e M iss i ss ipp i Sound, one h a l f o f t h e z o o p l a n k t e r s i n t h e summer a r e oys ter la rvae ( B u t l e r 1954). Abundance i s greatest a f t e r h igh t i d e (Andrews 1979). The d a i l y m o r t a l i t y o f l a r vae i s about 10% (Drinnan and S t a l l w o r t h y 1979) .

Newly s e t spat u s u a l l y a re dense on s u i t a b l e substrates. For exanple, i n Apalachicola Bay the re i s an average o f 2.5 spat s e t per s h e l l ( I n g l e 1951), o r 100 spat/m2 o f sur face area (Menzel e t a l . 1966). I n Alabama, t he re are on l y 0.06 spat/m2 i n Bayou Cour and 0. 17/m2 i n She1 lbank Bayou (Eckmayer 1977), where the re i s i n t e n s i v e shrimping, low DO, and s i l t a t i o n (Mark S. Van Hoose, pers. comm. 1. Ten m i les away i n Kings Bayou, spat dens i t y i s 1.2 t o 10.8/m . I n Louis iana, t h e d a i l y r a t e o f s e t t i n g a f t e r peak spawning i s as much as 90 spa t / she l l (Hopkins 1955). Chatry e t a l . (1983) observed se ts o f 10 t o 1,890 oysters/m2 i n Louisiana.

The e a r l y m o r t a l i t y o f spat has not been s tud ied i n t h e g u l f region. I n Massachusetts, t h e m o r t a l i t y du r i ng

t h e f i r s t mmth ranges f r o m 79% t o 99% (Kran tz and Chamber1 i n 1978). T y p i c a l annua l m o r t a l i t y o f s p a t i s 60% i n Lou i s i ana (Mackin 1961a) ; m o r t a l i t y i s u s u a l l y 90% t o 99% a t s p e c i f i c seed grounds (Chat ry e t a1 . 1983). Annual m o r t a l i t y o f seed oys te r s i s 6% t o 11% (Owen 1953a). Spat s u r v i v a l i s l e s s i n dense se t s t han i n sparse s e t s i n L o u i s i a n a ( C h a t r y e t a l . 1 9 8 3 ) and Chesapeake Bay (Webster and Shaw 1968). M o r t a l i t y tends t o be g rea te r i n sma l l seed oys te r s t han i n l a r g e ones. P roduc t i on of seed oys te r s i s n o t c l o s e l y c o r r e l a t e d w i t h t h e number o f s p a t (Chat ry e t a l . 1983).

The m o r t a l i t y o f oys te r s i n g u l f coas ta l waters v a r i e s g r e a t l y depending upon t h e r a t e o f f r eshwa te r i n f l o w and p r e d a t o r abundance. I n Texas, t h e m o r t a l i t y o f oys te r s f rom seed t o a d u l t ( 1 y e a r ) i s 90% (Gunter 1955). Under op t ima l cond i t i ons , t h e month ly m o r t a l i t y i s 2% t o 4% i n Lou i s i ana (Gunter 1953). Mack i n (1961a) c i t e d 60% as t h e annual m o r t a l i t y under p reva i 1 i n g c o n d i t i o n s o f s a l i n i t y and p reda to rs . Based on t h e number o f newly dead oys te rs , Ogle (1979) es t imated t h a t t h e month ly mor ta l i t y i n M i s s i s s i p p i ranged from 6% t o 36%. I n Lou is iana , newly dead o y s t e r s made up 5% t o 80% of t h e p o p u l a t i o n w i t h an average o f 27% (Owen e t a l . 1951). An e n t i r e p o p u l a t i o n of o y s t e r s i n some areas may be k i 1 1 ed by excess ive f r eshwa te r i n f l o w (and low s a l i n i t i e s ) f rom t h e M i s s i s s i p p i and Pear l R i ve rs (Gunter 1953; Schlesselman 1955; MacKenzie 1977), o r by h i gh wate r temperatures i n i s o l a t e d bays i n Texas (Copeland and Hoese 1966).

ECOLOGICAL ROLE

Larvae feed l a r g e l y on p lank ton , p a r t i c u l a r l y sma l l , naked f l a g e l l a t e s (chrysophy tes) (Gui 1 l a r d 1957). A t moderate wate r temperatures, l a r v a l growth i s bes t w i t h a d i e t o f naked f l a g e l l a t e s , whereas a t temperatures above 27 "C naked a lgae a r e scarce and

ch lo rophy tes a re more abundant as f ood (Davis and Calabrese 1964). B a c t e r i a a r e no t eaten by l a r v a e (Davis 1953).

Oys te r l a r v a e a r e f ood f o r a w ide v a r i e t y o f f i l t e r feeders (Andrews 1979).

A d u l t oys te rs f i l t e r l a r g e q u a n t i t i e s o f b rack i sh water . They most e f f e c t i v e l y f i l t e r p a r t i c l e s i n t h e 3- t o 4-wn s i z e range (Haven and Moral es-A1 amo 1970). Naked f 1 age1 - l a t e s a r e t h e most impor tan t f ood a l though b a c t e r i a a r e sometimes consumed, presumably because they a r e a t tached t o d e t r i t u s . Fo r each gram o f d r y w e i g h t o f t i s s u e , an o y s t e r h e l d a t 21 "C f i l t e r s 1.5 l / h r , w i t h a maximum o f 1.9 l / h r (Palmer 1980). A t temperatures above 25 O C about 8 l / h r a r e f i 1 t e r e d (Langefoss and Maurer 1975). The volume o f wa te r f i l t e r e d p e r hour i s about 1500 t imes t h e volume o f t h e o y s t e r ' s body (Loosanof f and Nomejko 1946 ) . The f i l t r a t i o n r a t e i s independent o f t h e a v a i l a b l e f ood supply , t h e s tage of t i d e , o r t h e t i m e of day. I f f o o d i s a b s e n t , however, t h e va lves a re c losed much o f t h e t i m e (H igg ins 1980).

The American o y s t e r i s t h e dominant species i n t h e o y s t e r r e e f community. Over 40 macrofaunal spe- c i e s o r g roups 1 i v e i n o y s t e r beds (Bahr and L a n i e r 1981), and t h e t o t a l number of species i n an o y s t e r community may exceed 300 (We1 1s 1961). On t h e o y s t e r r ee f , oys te r s a r e r espons ib l e f o r as much as 88% o f t h e r e s p i r a t i o n (Bahr and L a n i e r 1981).

Oys te rs a r e s u s c e p t i b l e t o a v a r i e t y o f diseases and p a r a s i t e s and a r e p r e y e d upon by s e v e r a l s p e c i e s ( G a l t s o f f 1964). The b a c t e r i a l diseases V i b r i o and Pseudomonas sometimes k i 11 oysters . The p ro tozoan pathogen ~ e r k i nsus mar inus. i n f e c t s oys te r s f r om Delaware t o Mexico. I n ~ i x a s , t h e i n d e x o f s t r e s s was i n d i r e c t r e l a t i o n t o t h e l e v e l of i n f e c t i o n (Soni a t and Koeni g 1982). I n F l o r i d a , i n f e c t i o n s o f t h e

pro tozoan become l e t h a l on l y d u r i n g e l e v a t e d summer wa te r temperatures (Qu ick and Mackin 1971). I n Texas, t h e p ro tozoan p a r a s i t e Labyr in thomyxa marina i s though t t o k i l l 10% t o 50% o t e a d u l t oys te r s ( H o f s t e t t e r 1977). Disease epidemics a r e common i n t h e g u l f r e g i o n (Mackin 1961b). I n L o u i s i a n a , a l l o y s t e r s i n some l o - c a t i o n s a r e i n f e c t e d w i t h t h e g r e g a r i ne p a r a s i t e Nemgop;!j; ost rearum, and i n F l o r i d a 9 i n f e c t e d (Owen e t a l . 1951). The p a r a s i t e , however, d i d n o t d i r e c t l y cause m o r t a l i ty.

Preda to rs o f t e n l i m i t t h e abundance o f oys te rs . The sou thern o y s t e r d r i 11, Tha is haemastoma, i s r espons ib l e f o r h e m a j o r i t y o f o y s t e r deaths i n Lou is iana , M i s s i s s i p p i , and Alabama. Other common p reda to r s a r e t h e l i g h t n i n g whel k (Busycon con t r a r i um) , t h e b l u e c rab ( C a l l i n e c t e s sap idus) , and t h e s t one c rab (Menippe mercenar ia ) (Ma rsha l l 1954; Menzel and N icky 1958; Cake 1983). A l l s i z e s o f oys te r s a r e k i l l e d by o y s t e r d r i l l s , which bore th rough t h e s h e l l s w i t h a combinat ion o f chemical d i s s o l u t i o n o f t h e s h e l l and d r i l l i n g ( r a d u l a r r asp i ng ) . B l u e crabs p r e f e r sma l l oys te r s ; s t one crabs w i l l c rush any s i z e o f o y s t e r t h a t t hey can manipu la te, as wi 11 seve ra l spec ies o f x a n t h i d mud crabs. The sou thern o y s t e r d r i l l o f t e n k i l l s w i t h o u t d r i l l i n g by r asp i ng a m inu te gap between t h e va lves and p r o t r u d i n g t h e p robosc i s i n t o t h e mant le c a v i t y (McGraw and Gunter 1972; Gunter 1979b). The crown conch (Melongena corona) i s a p r e d a t o r o f oys te r s a l ong F l o r i d a ' s west coas t . The sou thern o y s t e r d r i l l has been r e p o r t e d t o k i l l 50% o f t h e oys te r s o f p r o d u c t i v e r e e f s and 100% i n nonproduc t i ve reefs near Pass C h r i s t i a n , M i s s i s s i p p i (Chapman 1959), and 50% t o 85% o f t h e oys te r s i n Lou i s i ana (Schlesselman 1955). Souther? o y s t e r d r i l l s have d e n s i t i e s o f 201111 i n some o y s t e r r e e f s (Hopkins 1955), and a s i n g l e d r i l l can consume up t o 4 s p a t l h r ( B u t l e r 1954), o r up t o one a d u l t o y s t e r every 8 days

(Gunter 1979b). On S t . V incen t Bar i n Apa lach i co l a j a y , F l o r i d a , t h e r e were 2.8 d r i l l s l m , which t o g e t h e r w i t h s t one crabs des t r oyed 67% of t h e oys te r s i n one month (Menzel e t a l . 1957). The d r i 11 and t h e s tone c rab cause se r i ous m o r t a l i t y i n Texas (Gunter 1955) and F l o r i d a (Menzel e t a1 1966).

Menzel e t a1 . (1966) cons i de r t h e s t o n e c r a b t o be t h e m a i n enemy o f oys te r s i n F l o r i d a . The d e n s i t y o f t h e 2 s tone c rab i n Lou i s i ana i s l / m and each p o t e n t i a l l y consumes 219 oys te r s p e r year . I n l a b o r a t o r y exper iments , a b l u e c rab a t e 19 o y s t e r spa t l day , bu t d i d n o t consume a d u l t s un l ess t h e y were weakened (Menzel and Hopkins 1956). The b lack drum ( ~ o ~ o n i a s c romis ) , sou the rn eag le r ay (My1 i o b a t i s goode i ) , and cownose ray (Rh i nopte ra bonasus ) may des t r oy an o y s t e r reef by e a t i n g t h e spa t (Schlesselman 1955).

The o y s t e r c rab P inno theres l i v e s i n t h e mant le c a v i t y and may damage t h e g i 11s o f oys te r s (Schlesselman 1955). The widespread b o r i n g sponge C l i ona , and t h e b o r i n g clam i l o t h r a s m i t h i i ) weaken t h e oys- - and lowe r market q u a l i t y

(Schlesselman 1955). Spat a re preyed upon by t h e f l a t w o r m Sty lochus e l 1 i p - t i c u s (MacKenzie 1970; Ch r i s t ensen 1973). The sea anemone (Diadumene leuco lena) consumes 0.6 t o 4.9 o y s t e r l a r v a e p e r m inu te i n t h e l a b o r a t o r y and a l s o feeds on l a r v a e i n t h e n a t u r a l env i ronment ( S t e i nberg and Kennedy 1979).

M a j o r c o m p e t i t o r s f o r space on s u b s t r a t e a r e t h e s l i p p e r s h e l l s (C rep idu l a spp.) and t h e j i n g l e s h e l l s (Anomia spp.) as w e l l as barnac les and o t h e r oys te r s t h a t s e t on a d u l t s h e l l s (MacKenzie 1970). The hooked mussel ( I schad ium recurvum) competes w i t h oys te r s f o r space and food i n Lou i s i ana (Schlesselman 1955). A heavy s e t of t h e barnac le Balanus improv isus can s e r i o u s l y reduce t h e area o f ha rd su r face a v a i l a b l e t o

oys te r s ( I n g l e 1951). Accord ing t o I n g l e (1951), s l i p p e r s h e l l s and t h e hooked mussel a re n o t se r i ous compet- i t o r s w i t h oys te rs i n Apa lach i co la Bay, F l o r i d a . Young oys te r s may be smothered by t h e exc re ta o f po lychaete worms o f t h e genus P o l y d o r a , o r by exc re ta o f a d u l t oys te rs (S tenze l 1971). Blooms o f red t i d e (Co- c h l o d i nium he te ro loba tum) a t concen- t r a t i o n s o f 500 c e l l s / m l k i l l o y s t e r l a r v a e (Ho and ~ u b k o f f . l 9 7 9 ) .

"

ENVIRONMENTAL REQUIREMENTS

The American o y s t e r t y p i c a l l y l i v e s i n sha l low, we l l -m ixed es tua r - i e s , lagoons, and oceanic bays where i t t o l e r a t e s w i d e l y f l u c t u a t i n g water temperatures , s a l i n i t i e s , and concen t ra t i ons o f suspended s o l i d s (Andrews 1979). Because o f t o l e r a n c e t o t hese f l u c t u a t i o n s , p r e c i s e env i ronmental requ i rements a lone o r i n combinat ion a r e d i f f i c u l t t o de f ine .

Temperature

I n 1 abo ra to r y t e s t s , embryos develop normal l y a t temperatures between 20 and 30 "C bu t abnormal- i t i e s i nc rease p rog ress i ve l y when temperatures d e c l i n e t o 15 "C o r r i s e t o 35 "C (MacInnes and Calabrese 1979). On t h e o t h e r hand, Dupuy (1975) i n h i s experiments r epo r t ed t h a t embryo abno rma l i t i e s cou ld be as h i g h as 2% a t 25 "C and 12% a t 30 "C. The growth o f l a r v a e may be impa i red by w a t e r t e m p e r a t u r e s o f 30 "C and h i ghe r , and even a b r i e f exposure f o r 10 min a t wa te r temperatures near 40 "C r e t a r d s g r o w t h ( H i d u e t a l . 1 9 7 4 ) . I n o t h e r t e s t s , g row th was f a s t e s t and s u r v i v a l h i g h e s t a t water temperatures o f 27.5 t o 32.5 "C (Davis and Calabrese 1964). These t e s t s were a l l conducted on o y s t e r s tocks from t h e A t l a n t i c coas t and exact temperature ranges may no t apply t o o y s t e r embryos o r l a r v a e f r om t h e Gulf o f Mexico.

A d u l t s e x i s t w i t h i n a r ange o f water temperatures f r om -2 "C i n New England t o 36 "C i n t h e G u l f o f Mexico. Dur ing low t i d e , oys te rs may be exposed t o and s u r v i v e a i r temper- a tu res below f r e e z i n g o r above 49 "C ( G a l t s o f f 1964). Excess i ve l y h i gh ter rperatu res cause m o r t a l i t y ; water temperatures above 35 "C f o r t h e whole t i d a l c y c l e i n I n d i a n R i v e r bay, Delaware, a r e known t o have k i l l e d some oys te r s (Tinsman and Maurer 1974). The c r i t i c a l thermal maximum determined i n t h e l a b o r a t o r y f o r t h e American o y s t e r i s 48 "C (Henderson 1929). Oysters t o l e r a t e f r e e z i n g o f t h e i r t i s s u e s , and r e v i v e a f t e r thaw- i n g (Loosanof f 1965a). Gu l f coast oys te r s , however, appa ren t l y a r e no t as t o l e r a n t o f f r e e z i n g (Cake 1983).

Optimum water temperatures f o r growth, reproduct ion , and s u r v i v a l o f American oys te r s range f r om about 20 t o 30 "C, and t h e response o f oys te rs t o tempera tu re changes and extremes depend on an i n t e r a c t i o n o f env i ronmenta l cond i t i ons . The r a t e t h a t water i s pumped th rough t h e o y s t e r ' s g i l l system i s determined by temperature. A water temperature range of 20 t o 25 "C r e s u l t s i n f a v o r a b l e pumping ra tes f o r supp l y i ng needs f o r oxygen, food, and waste d i sposa l ( C o l l i e r 1951). Oysters a re r e l a t i v e l y i n a c t i v e be low 7 "C and pumping i s g r e a t l y reduced. Although t h e t h r e s h o l d f o r f eed ing by Chesapeake Bay oys te r s i n t h e l a b o r a t o r y i s 3 "C (Haven and Morales-Alamo 1966), few New England oys te rs feed a t temperatures below 8 "C and growth ceases ( P r i c e e t a l . 1975). Some growth has been repo r t ed i n Long I s l a n d Sound i n t h e w i n t e r when water i s unseasonably warm and f ood i s a v a i l a b l e (Ruddy e t a l . 1975). Growth o f Long I s l a n d Sound oys te rs i s p o s s i b l e between 6 and 32 "C and f a s t e s t near 26 "C ( G a l t s o f f 1964). The exposure o f F l o r i d a a d u l t s t o a 35 "C water temperature acce le ra ted gametogenesis and spawning, bu t t h e exposure p reven ted subsequent spawning i n t h a t y e a r (Qu ick 1971).

D i f f e r e n c e s i n thermal r e q u i r e - ments o f oys te rs f r om d i f f e r e n t areas have l e d t o t h e p o s t u l a t i o n t h a t races may be separated on t h e bas is o f tem- pe ra tu r e requirements (Ahmed 1975). Spawning temperatures f o r t h r e e d i s - t i n c t races were r e p o r t e d by Stauber (1950): 16 OC f o r t h e no r t he rn race (New England), 20 OC f o r t h e m i d - A t l a n t i c race, and 25 O C f o r t h e G u l f o f Mexico race. For instance, oys te r s spawn i n Galveston Bay, Texas, a f t e r temperatures exceed 25 OC (Hop- k i n s 1931), and mass spawnings i n Apa lach i co la Bay, F l o r i d a , do n o t t a k e p l a c e u n t i l temperatures exceed 26 O C

( I n g l e 1951). A d d i t i o n a l ev idence f o r t h e ex i s t ence of p h y s i o l o g i c a l races was r e p o r t e d by Menzel ( 1 9 5 5 ) , who found t h a t c i l i a r y a c t i v i t y cont inues a t 0 OC i n no r t he rn oys te r s bu t ceases a t 6 O C i n sou thern oys te rs . Andrews (1979) be1 ieves t h e r e a r e o t h e r races as w e l l , bu t gene t i c s t u d i e s do no t c l o s e l y suppor t t h e ex i s t ence o f phys- i o l o g i c a l races. Buroker e t a l . (1979) found t h a t a l l oys te r s s t u d i e d were g e n e t i c a l l y i d e n t i c a l , except those f r om Nova S c o t i a and F l o r i d a . These popu la t i ons were 82% s i m i l a r , about t h e l e v e l o f s i m i l a r i t y between t h e American and mangrove oys te r s , which can successfu 1 l y h y b r i d i z e (Menzel 1968). Accord ing t o Groue and L e s t e r (1982), oys te r s i n Laguna Madre, Texas, a r e g e n e t i c a l l y d i s t i n c t f r om f o u r o t h e r g u l f popu la t i ons . Measurement o f isozymes i n t h e gene t i c s t ud ies , however, may n o t v a l i d a t e these f i n d i n g s .

S a l i n i t y

A d u l t oys te r s i n t h e G u l f o f Mexico norma l l y occur a t s a l i n i t i e s between 10 and 30 p p t bu t they t o l e r a t e a s a l i n i t y range o f 2 t o 40 p p t (Gunter and Geyer 1955); o u t s i d e t h i s range, they d i e o r d i scon t i nue feed ing and reproduc t ion . I n t h e M i s s i s s i p p i Sound, s a l i n i t i e s among p r o d u c t i v e r e e f s range f r o m 2 t o 22 p p t ( E l e u t e r i u s 1977). The optimum s a l i n i t y range o f t h e American o y s t e r

i n Long I s l a n d Sound i s 10 t o 28 p p t (Loosanof f 1965a), bu t most oys te r s f r om Long I s l a n d Sound s u r v i v e 3 p p t f o r up t o 30 days i n t h e l a b o r a t o r y (Loosanof f 1965b). H igh mor ta l i t y was r e p o r t e d d u r i n g extended exposure o f o y s t e r s t o f reshwater ( t 2 p p t s a l i n i t y ) d u r i n g s p r i n g f l o o d s i n M i s s i s s i p p i Sound and Lou i s i ana marshes (Gunter 1953), i n Mob i l e Bay, Alabama (May 1972), and i n t h e Santee R i ve r , South Caro l i na (Bu r re l 1 1977). Many o y s t e r s d i e d i n t h e Beau fo r t I n l e t , N o r t h Ca ro l i na , a f t e r exposure t o 5 p p t f o r about a month (Wel ls 1961). Oysters i n one Lou i s i ana r e e f d i e d a f t e r 14 days a t 6 p p t (Anderson and Anderson 1975), a l t hough most o y s t e r s i n Lou i s i ana coas ta l waters t o l e r a t e lower s a l i n i t i e s : Gunter (1953) r e p o r t e d t h a t a s a l i n i t y o f l e s s t h a n 2 p p t f o r 14 days k i l l e d o n l y 12% o f a p o p u l a t i o n o f oys te r s .

Oysters appa ren t l y t o l e r a t e h i g h e r s a l i n i t i e s i n Texas t h a n e l sewhere. I n Laguna Madre, a s a l t w a t e r bay t h a t o f t e n has unusua l l y h i g h s a l i n i t i e s , oys te rs spawn and grow i n s a l i n i t i e s g r e a t e r t han 40 p p t (Breuer 1962). I n Red f i sh Bay and Harbor I s land , Texas, mass m o r t a l i t y occur red a t a s a l i n i t y o f 40 p p t b u t t h e o y s t e r s a l s o were exposed t o a wa te r temperature of 37 O C (Copeland and Hoese 1966).

S a l i n i t y requi rements o r t o l e r - ance v a r y f r o m p l a c e t o p l a c e f o r d i f f e r e n t l i f e s tages and a c t i v i t i e s . I n t h e G u l f o f Mexico, bes t growth and rep roduc t i on i s i n o y s t e r r e e f s w i t h a s a l i n i t y o f 12 t o 30 p p t , bu t o y s t e r abundance i s g r e a t e s t a t 10 t o 20 p p t ( B u t l e r 1954). I n Long I s l a n d Sound, s a l i n i t i e s above 7 p p t a re r e q u i r e d f o r spawning (Loosanof f 1948). Unusual ly h i g h f r eshwa te r i n f l o w i n Mob i l e Bay, Alabama, i n h i b i t s t h e ma tu ra t i on and spawning o f oys te r s (May 1972). Excess i ve l y low s a l i n i t y i n h i b i t s gonadal ma tu ra t i on i n oys te r s i n Chesapeake Bay ( B u t l e r 1949) and Long I s l a n d Sound (Loosanoff 1953). Reproduc t i ve f a i l u r e may be a d i r e c t

e f f e c t o f s a l i n i t y o r i t m i g h t be i n d i r e c t l y caused by i n s u f f i c i e n t f e e d i n g a t low s a l i n i t y .

I n t h e l abo ra to r y , A t l a n t i c coas t embryos develop norma l l y a t s a l i n i t i e s o f 16 t o 30 p p t (MacInnes and Cala- brese 1979). A t l a n t i c coast l a r v a e t o l e r a t e s a l i n i t i e s o f 3 t o 3 1 p p t ( C a r r i k e r 1951), bu t grow f a s t e s t and s u r v i v e bes t a t s a l i n i t i e s above 12 p p t (Davis and Calabrese 1964). La r - vae i n a New Jersey es tua ry move t o t h e ha1 o c l i ne ( t h e boundary between l o w s a l i n i t y w a t e r and deepe r h i g h s a l i n i t y wa te r ) where s a l i n i t i e s a r e above 5 p p t ( C a r r i k e r 1951 ) . The minimum s a l i n i t y f o r good p r o d u c t i o n o f l a r v a e i n Galveston Bay, Texas, i s about 20 pp t , p robab ly because f ood i s more abundant a t these s a l i n i t i e s (Hopkins 1931). I n general , spa t s e t t i n g i s l ess a t lower s a l i n i t i e s (Menzel e t a l . 1966). I n a 10-year s tudy a t t h r e e s i t e s near B re ton Sound, Lou is iana , optimum s a l i n i t i e s f o r spa t p r o d u c t i o n were 6 t o 8 p p t i n May and 3 p p t i n June and J u l y (Chat ry e t a l . 1983). Optimum s a l i n i t i e s f o r t h e growth o f spa t a r e 15 t o 22 p p t (Chanley 1957).

Heavy f r eshwa te r i n f l o w sometimes g r e a t l y b e n e f i t s o y s t e r popu la t i ons by k i 11 i ng p reda to r s t h a t cannot t o l e r a t e low s a l i n i t y water (Owen 1953b; Marshal 1 1954). For exarnpl e, t h e southern o v s t e r d r i l l and t h e whelk (Bus con c a r i c a ) d i e a t sa l i n i t i e s& l l ~ ( W e l l s 1961). and s tone c rabs succumb a t s a l i n i t i e s below 1 5 p p t (Menzel e t a l . 1966).

Subs t ra te

The p r e f e r r e d h a b i t a t s i n t h e G u l f o f Mexico a r e sha l l ow bays, mud f l a t s , and o f fshore sandy bars ( B u t l e r 1954; Copeland and Hoese 1966; Menzel e t a l . 1966). Oysters grow e q u a l l y w e l l on rocky bottoms o r on mud w i t h a cons is tency t h a t w i 11 h o l d t h e o y s t e r on t h e sur face , A l though most o y s t e r r ee f s a r e on f i r m bottoms ( P r i c e

1954), t hey may a l s o be abundant on mud bottoms sur round ing t h e ree fs ( B u t l e r 1954; Menzel e t a l . 1966 ) . Oysters f r o m muddy subs t ra tes a r e more s l ende r t han those f r o m ha rd sub- s t r a t e s (Gal t s o f f 1964). Maximum s e t t i n g i s on h o r i z o n t a l sur faces (Cl ime 1976). I n Galveston Bay, Texas, oys te r s t h r i v e on bottoms t h a t a r e 17% t o 100% sand ( H a r r y 1976 ) . The weather ing o f s h e l l s produces g r i t which i s thought t o c l ean o y s t e r she1 1s of f o u l i n g organisms (Gunter 1979a).

Cur ren ts

Cur ren ts a r e p a r t i c u l a r l y impor tan t t o American o y s t e r l a r v a e and adu l t s . Fo r maximum feed ing , t h e volume o f water immediate ly above an o y s t e r bed must be renewed by a moderate c u r r e n t 72 t imes every 24 h ( G a l t s o f f 1964). T i d a l f l o w s o f 156 t o 260 cm/sec o r h i g h e r a r e needed f o r optimum growth i n M i s s i s s i p p i (Veal e t a l . 1972). Cur ren ts a re necessary f o r removal o f feces and pseudofeces t o p reven t b u r i a l o f t h e oys te r reef (Lund 1957; S tenze l 1971). Cur ren ts on t h e s i t e s o f o y s t e r bars i n Beau fo r t I n l e t and t h e Newport R i v e r es tua ry i n Nor th C a r o l i n a a re 11 t o 66 cm/sec (We1 1s 1961). Turbu len t cu r ren t s t h a t c a r r y sand and pebbles, however, can damage oys te r s by e rod ing s h e l l s u r f a c e s ( G a l t s o f f 1964 ) . A v e l o c i t y o f 150 cm/sec was observed t o cause unat tached oys te rs t o tumble a l ong t h e bot tom o f Long I s l a n d Sound (MacKenzie 1981). I n Delaware Bay, oys te r s a r e most abundant i n areas o f scour where c u r r e n t s keep t h e o y s t e r beds f r e e o f sediments (Keck e t a1 . 1973).

Oxygen

The h o u r l y oxygen consumption i s 39 ml /kg f o r a whole animal i n c l u d i n g t h e s h e l l o r 303 ml /kg o f wet t i s s u e (Hammen 1969). Oxygen consumption

I increases w i t h i ncreas i ng temper-

a t u r e ( F i g u r e 3); Q values ( t h e f a c t o r by which a reaction v e l o c i t y i s inc reased by an i nc rease i n temperature o f 10 "C) range f r om 1.2 t o 2.3 f o r g i l l t i s s u e and 2.7 t o 4.2 f o r mant le t i s s u e (Bass 1977). Oys- t e r s a r e f a c u l t a t i v e anaerobes and a re ab le t o s u r v i v e d a i l y exposure t o low oxygen. I n 1971, low oxygen k i l l e d o y s t e r s and reduced t h e s e t t i n g o f spa t i n Mob i l e Bay, Alabama (May 1972 ) . Oxygen consump t i on i s z e r o when t h e v a l v e s a r e c l o s e d (Hammen 1969), b u t an oxygen debt b u i l d s up.

F i g u r e 3. Oxygen consumption i n t h e American o y s t e r as a f u n c t i o n o f s a l i n i t y and temperature (Shumway 1982).

Suspended So l i ds and Sedimentat ion

Extreme cond i t i ons , such as those assoc ia ted w i t h l a r g e storms, can p r a c t i c a l l y des t roy an o y s t e r ree f . The l a r g e decrease i n o y s t e r meat land ings i n Alabama f rom 1979 t o 1980 i s .a r e s u l t o f H u r r i c a n e F r e d e r i c k which s t r u c k Alabama i n September

1977. The s t o r m k i l l e d o y s t e r s by cove r i ng some ree f s w i t h mud and washing t h e s u b s t r a t e o f f o thers (Mark S. Van Hoose, pers. comm.). Suspended s o l i d s may c l o g g i l l s and i n t e r f e r e w i t h f i l t e r f e e d i n g and r e s p i r a t i o n (Cake 1983). Oysters t o l e r a t e water w i t h suspended s o l i d s , b u t t h e pumping r a t e decreases. I n t h e 1 aboratory , pumping i s reduced 70% t o 85% over t h e range 0 t o 1 g / l , depend ing on t h e na tu re o f t h e suspended sediment (Loosanof f and Tommers 1948). I n n a t u r a l env i ronments oys te r s appa ren t l y develop and grow b e t t e r i n waters w i t h h i g h concent ra t ions o f suspended s o l i d s than i n waters w i t h low concen t ra t i ons (Rhoades 1973).

I f covered w i t h sediment, oys te r s d i e i n 1 week a t 20 "C and i n 2 days a t 25 OC (Dunnington 1968). The m o r t a l i t y o f oys te r s covered w i t h 2 t o 5 cm o f s e d i m e n t n e a r one d r e d g i n g s i t e i n L o u i s i a n a i n c r e a s e d by 48% (Rose 1973 ) . I n Alabama, however , muddy water f rom dredg ing gene ra l l y d i d no t harm nearby o y s t e r r e e f s because cu r r e n t s and g r a v i t y c a r r i e d t h e muddy wate r away f r om t h e e l eva ted o y s t e r r e e f s (May 1976).

Other Envi ronmenta l Requirements

Oys te r embryos develop normal l y w i t h i n a pH r a n g e o f 6.75 t o 8.75 (Calabrese and Davis 1966), and develop abnormal ly a t a pH above 9.0 and below 6.5. Larvae t o l e r a t e t h e same pH range as embryos bu t growth i s f a s t e s t a t a pH o f 8.25 t o 8.5.

Oys te r s occur a t depths o f 0.3 m above t o 12 m be low mean l o w t i d e ( B u t l e r 1954).

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Keck, R., D. Maurer, and L. Wat l ing . 1973. T i d a l s t ream development and i t s e f f e c t on t h e d i s t r i b u - t i o n o f t h e American oys te r . Hydrob io l og ia 42(4 ) : 369-379.

K i lgen , R.H., and R.J. Dugas. 1984. The e c o l o g y o f o y s t e r r e e f s o f t h e n o r t h e r n G u l f o f Mex ico : A cormun i ty p r o f i l e . U.S. F i s h W i l d l . Serv. B i o l . Rep. ( i n prep

Ko r r i nga , P. 1976. Farming t h e cupped oys te r s o f t h e genus Crassostrea: A m u l t i d i s c i p l i n a r y t r e a t i s e . E l s e v i e r , Amsterdam. 238 pp.

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Langefoss, C.M., and D. Maurer. 1975. Energy p a r t i t i o n i n g i n t h e Amer- i c a n oys te r , Crassost rea v i r g i n- i ca (Gmel i n ) . Proc. Na t l . She1 l- 7 f i s h . Assoc. 65:20-25.

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Loosanof f , V.L., and C .A. Nomejko. 1951. Spawn ing and s e t t i n g o f t h e American oys te r , 0. v i r g i n i c a i n r e l a t i o n t o l u n a r phase. Ecology 32(1) : 223-234.

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Lu tz , R., J. Goodsel l , M. Castagna, S. Chapman, C. Newel l , H. Hidu, R. Mann, D. Jab lonsk i , V. Kennedy, S. S i d d a l l , R. Goldberg, H.

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Menzel, R.W. 1955. Some phases o f t h e b i o l o g y o f Ostrea e q u e s t r i s and a comparison w i t h Crassos t rea c- i n i c a (Gmelin). Publ. I n s t . Mar. h n i v . Tex. 4:69-153.

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Menzel , R.W., and F.E. Nicky. 1958. S tud ies o f t h e d i s t r i b u t i o n and f eed ing h a b i t s o f some o y s t e r p reda to rs i n A1 li g a t o r Harbor, F l o r i d a . B u l l . Mar. Sc i . Gu l f Ca r i bb. 8 (2 ) : 125-145.

Menzel, R.W., N.C. Hu l ings , and R.R. Hathaway. 1957. Causes of d e p l e t i o n of oys te r s i n St. V incent Bay, Apa lach i co la Bay, F l o r i d a . Proc. N a t l . Shel l f i s h . Assoc. 48: 66-71.

Menzel, R.W., N.C. Hu l i ngs , and R.R. Hathaway. 1966. Oys te r abundance i n Apa lach i co la Bay, F l o r i d a , i n r e l a t i on t o b i o t i c assoc ia t i ons i n f luenced by s a l i n i t y and o t h e r f a c t o r s . Gu l f Res. Rep. 2(2):73- 96.

Newkirk, G.F., L.E. Haley, D.L. Waugh, and R. Doyle. 1977. Genet ics o f l a r v a e and s p a t g r o w t h r a t e i n t h e o y s t e r ~ r a s s o s t r e a v i r i n i c a . Mar. B i o l . (Be r l . ) 41(1 + :49-52.

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Owen, H.M. 1953b. The r e l a t i o n s h i p o f h i g h t enpe ra tu re and low r a i n f a l l t o o y s t e r p r o d u c t i o n i n L o u i s i - ana. B u l l . Mar. Sc i . Gu l f Car ibb. 3(1) : 34-43.

Owen, H.M., L.L. W a l t e r s , and L.A. Bregan. 1951. E t i o l o g i c a l s t ud ies on o y s t e r m o r t a l i t y . I. Nemato s i s ost rearum Pry therch ,

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Pa r r i sh , F.K. 1969. E a r l y mol luscan development . Proceedings o f t h e conference on s h e l l f i s h c u l t u r e . Regional Mar i ne Resources Coun- c i l , Hauppauge, N.Y.

Pausina, B.V. 1971. Lou i s i ana o y s t e r c u l t u r e . P r o c . 1 s t Annu. Meet . Wor ld M a r i c u l t . Soc. 1: 29-34.

P ie rce , M.E., and J.T. Conover. 1954. A s tudy o f t h e growth of oys te rs u nder d i f f e r e n t eco l o g i c a l con- d i t i o n s i n Great Pond. B i o l . B u l l . (Woods Hol e ) 107: 318. (Abs t r . )

Pol l a r d , J .F. 1973. Experiments t o r ees tab l i s h h i s t o r i c a l o y s t e r seed grounds and t o c o n t r o l t h e sou thern o y s t e r d r i 11. La. W i l d l . F ish . Comm. Tech. B u l l . 6. 82 PP.

P r i ce , W.A. 1954. Oys te r reefs of t h e Gu l f o f Mexico. U.S. F i s h W i l d l . Serv. F ish. B u l l . 55(89): 491.

P r i ce , A.H., C.T. Hess, and C.W. Smith. 1975. Observat ions of Crassost rea v i r g i n i c a c u l t u r e d i n t h e heated e f f l u e n t and d i s - charged rad ionuc l i des of a n u c l e a r power r eac to r . Proc. N a t l . Shel l f i s h . Assoc. 66:54-68.

Pruder, G.D. 1975. Eng inee r i ng aspects o f b i v a l v e mol luscan m a r i c u l t u re: cu 1 t u r e sys tem con f i gu r a t i ons . Col lege o f Mar ine Studies, U n i v e r s i t y o f Delaware, Newark. 13 PP.

Qu ick , J.A., Jr. 1971. Pa tho log i ca l and p a r a s i t o l o g i c a l e f f e c t s of e l eva ted temperatures on t h e oys- t e r Crassost rea v i r g i n i c a w i t h emphasis on t h e pathogen Lab r i n - +- thomyxa marina. Pages 105-1 1 fi J.A. Quick, Jr. , ed. A p r e l i m i - nary i n v e s t i g a t i o n : t h e e f f e c t of e l eva ted temperature on t h e Amer- i c a n o y s t e r Crassos t rea v i r g i n i c a (Gmel in) . F l a . Dep. Nat. Resour. P ro f . Pap. Ser. 15. 190 pp.

Q u i c k , J.A., Jr., and J.G. Mack in . 1971. Oys te r p a r a s i t i s m by L a b y r i nthomyxa marina i n F l o r i d a . F la . Dep. Nat. Resour. Mar. Res. Lab. P ro f . Pap. Ser. 13: l -55.

Rhoades, D.C. 1973. The i n f l u e n c e o f depos i t - f eed ing benthos on water t u r b i d i t y and n u t r i e n t r ecyc l ing . Am. J. Sci. 273: 1-22.

R i t c h i e , T.P., and R.W. Menzel. 1969. I n f l u e n c e o f l i g h t on l a r v a l se t t l emen t o f American oys te rs . Proc. Na t l . S h e l l f i s h . Assoc. 59: 116-120.

Rockwood, C.E., and W.F. Mazek. 1977. Seasonal v a r i a t i o n s i n o y s t e r meat y i e l d s i n Apa lach ico la Bay, F l o r i d a . B u l l . Mar. Sc i . 27(2): 346-347.

Rose, C.D. 1973. M o r t a l i t y o f market- s i z e d oys te rs C rassos t rea v i r i n i c a i n t h e v i c i n i t y o f a 6%- r e g~ ng opera t ion . Chesapeake Sc i . 14(2) : 135-138.

Soniat , T.M., and M.L. Koenig. 1982. The e f f e c t o f p a r a s i t i s m by Perk i nsus mari nus . on t h e f r e e amino a c i d c o m ~ o s i t i o n o f Crassostrea v i r g i n i c a mant le t i s s u e . J. S h e l l f i s h Res. 2 [1 ) :

S t a u b e r , L.A. 1950. The p r o b l e m o f p h y s i o l o g i c a l species w i t h spe- c i a l re fe rence t o oys te rs and o y s t e r d r i l l s . ~co lo -gy 31:109- 118.

Ste inberg, P.D., and V.S. Kennedy. 1979. Predat ion upon Crassostrea v i r g i n i c a (Gmelin) l a r v a e by two i n v e r t e b r a t e species common t o Chesapeake Bay oys te r bars. Vel i ger 22: 78-84.

Stenzel , H.B. 1971. Oysters. Pages

Ruddy, G.M., S.Y. Feng, and G.S. N953-N1224 i n K.C. Moore, ed. Campbell. 1975. The e f f e c t o f T r e a t i s e on i n v e r t e b r a t e paleon- pro longed exposure t o e l eva ted t o l ogy . Pa r t N, Vol. 3. Mol lusca temperatures on t h e b iochemical 6. Geol. Soc. Am., Boulder, cons t i t uen t s , gonadal develop- Colo. and U n i v e r s i t y o f Kansas, ment, and s h e l l d e p o s i t i o n o f t h e Lawrence. American oys te r , Crassostrea v i r g i n i ca. Comp. B i ochem. Phys io l . 51B(2): 157-164.

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mariage. 1977. She1 l f i s h Birkenhead, England. 209 pp.

PAGE ] B i o l o g i c a l Report 82(11.64)* ] 4. TbIIa and Subtatla L n*oon DS~.

Species P r o f i l e s : L i f e Hi s t o r i e s and Environmental I

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Species p r o f i l e s a r e 1 i t e r a t u r e summaries o f t h e taxonomy, morphology, 1 i f e h i s t o r y , and environmental requ i rements o f coas ta l a q u a t i c spec ies . They a r e designed t o a s s i s t i n environmental impact assessment. The American o y s t e r , Crassost rea v i r g i n i c a , i s an impor tan t commercial species. Spawning occurs r e p e a t e d l y d u r i n g warmer months w i t h m i l l i o n s o f eggs re leased. Embryos and l a r v a e a r e c a r r i e d by c u r r e n t s th roughout t h e e s t u a r i e s and oceanic bays where t h e y occur. The s u r v i v i n g l a r v a e cement themselves t o a s o l i d o b j e c t , where they remain f o r t h e remainder of l i f e . Unable t o move, t hey must t o l e r a t e changes i n t h e environment t h a t range f rom -2 t o 36 O C ( a i r temperature) , 2 t o 40 p p t s a l i n i t y , and c l e a r o r muddy water . The d e n s i t y and occurrence o f a d u l t s i s l i m i t e d by p reda to rs , c h i e f l y o y s t e r d r i l l s , whelks, f i s h , and crabs. I

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E s t u a r i e s F i s h e r i e s Oxygen consumption Oysters Sal i n i t y L i f e c y c l e s Growth Temperature Feeding H a b i t s Suspended sediments

American o y s t e r Spawning Crassost rea v i r g i n i c a S a l i n i t y requ i rements Temperature r e q u i rements

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DEPARTMENT OF THE INTERIOR U.S. FISH AND WILDLIFE SERVICE

As the Nation's principal conservation agency. the Department of the Interior has responsibility for most of our.nationally owned public lands and natural resources. This includes fostering the wisest use of our land and water resources, protecting our fish and wildlife, preserving theenvironmental and cultural values of our national parks and historical places, and providing for the enjoyment of life through outdoor recreation. The Department as- sesses our energy and mineral resources and works to assure that their development is in the best interests of all our people. The Department also has a major responsibility for American Indian reservation communities and for people who live in island territories under U.S. administration.

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Species Profiles: Life Histories and Environmental ...aquaticcommons.org/3579/1/1986_stan.pdfoccurs from the Gulf of St. Lawrence, Canada, to Key Bi scayne, Florida. This species was