An Estuarine Bentic Index of Biotic Integrity IBI

8/8/2019 An Estuarine Bentic Index of Biotic Integrity IBI

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Estuaries Vol. 20, No. 1, p. 149-1 58 March 1997

An Estuar ine Benth ic

Biotic Integrity (B-IBI)C h e s a p e a k e B a y

Index o f

fo r

S T E I ' H E N B . W E I S B E R G L 9

j . A N A N D A R A N A S I N G I IEVersar, Inc.9200 Rumsey RoadColumbia , Maryland 21045

L I N D A C . S C H A F F N E R

ROBERT J. DIAZSchool of Mar ine ScienceThe C ol lege of W il liam a nd Ma ryGloucester Point, Virginia 2 30 62

DANIEL M. DAUER

Depa rtment of Biological SciencesOld Do min ion UniversityNorfolk, Virgin ia 23 52 9

JE~'FREY B .F R I T H S E NVersar, Inc.9200 Rum~wy RoadColumbia , Maryland 21045

A B S T R A C T : A m u l t i m e t r i c b e n t h i c i n d e x o f b i ot i c i n te g r it y ( B -I B I) w a s d e v e l o p e d u s i n g d a t a f r o m f i v e C h e s a p e a k eB a y s a m p l i n g p r o g r a m s c o n d u c t e d b e t w e e n 1 9 72 a n d 1 9 91 . A t t r i b u te s o f t h e i n d e x w e r e s e l e c t e d b y c o m p a r i n g t h er e s p o n s e o f 1 7 c a n d i d a t e m e a s u r e s o f b e n t h i c c o n d i t i o n ( m e t ri c s ) b e t w e e n a s e t o f m i n i m a l l y a f f e c t e dr e f e r e n c e s i t e sa n d a t a ll o t h e r s i t e s f o r w h i c h d a t a w e r e a v a i l ab l e. T h i s p r o c e d u r e w a s c o n d u c t e di n d e p e n d e n t l y f o re a c h o f s e v e nh a b i t a t s d e f i n e d b y s a l in i t y a n d s u b s t r a t e . F i f t e e n o f t h e 1 7 c a n d i d a t e m e t r i c s d i f f e r e d s i g n i f i c a n t l y b e t w e e n r e f e r e n c es i t e s a n d o t h e r s i t e s f o r a t l e a s t o n e h a b i t a t . N o m e e r i c d i f f e r e d s i g n i f i c a n tl y i n a ll s e v e n h a b i t a t s ; h o w e v e r , f o u r m e t r i c s ,s p e c i e s d i v e r s it y, a b u n d a n c e , b i o m a s s , a n d p e r c e n t o f a b u n d a n c e a s p o l l u t io n - i n d i c a t i v e t a x a, d i f f e r e d i n s ix h a b i t a t s .T h e i n d e x w a s c a l c u la t e d b ys c o r i n g e a c h s e l e c t e d m e t r i c a s 5 , 3 , o r 1 d e p e n d i n g o n w h e t h e r i t s v a l u e a t a s i t e a p p r o x -i m a t e d , d e v i a t e d s l i g h t ly f r o m , o r d e v i a t e d g r e a t l y f r o m c o n d i t i o n s a t t h e b e s t r e f e r e n c e s i t e s . Va l i d a t i o n b a s e d o ni n d e p e n d e n t d a t a c o l l e c t e d b e t w e e n 1 9 9 2 a n d 1 9 9 4 i n d i c a t e d t h a t t h e i n d e x c o r r e c t l y d i s t i n g u i s h e d s l x e s s e d s i t e s f r o mr e f e r e n c e s i t e s 93% o f t h e t i m e , w i t h t h e h i g h e s t v a l i d a t i o n r a t e s o c c u r r i n g i n h i g h s a l i n i t y h a b i t a t s .

I n t r o d u c t i o n

B e n t h i c i n v e r t e b r a t e s a r e u s e d e x t e n s i v e l y a s i n -d i c a t o r s o f e s t u a r i n e e n v i r o n m e n t a l s t a tu s a n dt r e n d s b e c a u s e n u m e r o u s s tu d ie s h a v e d e m o n s t r a t-e d t h a t b e n t h o s r e s p o n d p r e d i c t a b l y t o m a n y k in d so f n a t u r a l a n d a n t h r o p o g e n i c s tr e ss ( P e a r s o n a n dR o s e n b e r g 1 9 7 8 ; D a u e r 1 9 93 ; T a p p e t a l. 1 99 3 ; Wi l-s o n a n d J e f f r e y 1 9 9 4 ) . M a n y c h a r a c t e r i s t i c s o f b e n -t h i c a s s e m b l a g e s m a k e t h e m u s e f u l i n d i c a t o r s ( B i l -y a r d 1 9 8 7) , t h e m o s t i m p o r t a n t o f w h i c h a r e r e l at -e d t o t h e i r e x p o s u r e t o s t re s s a n d t h e d i v e r s it y o ft h e i r r e s p o n s e . E x p o s u r e t o h y p o x i a i s t y p i c a ll yg r e a t e s t in n e a r - b o t t o m w a t e r s a n d a n t h r o p o g e n i cc o n t a m i n a n t s o f t e n a c c u m u l a t e in se d i m e n t sw h e r e b e n t h o s l i v e . B e n t h i c o r g a n i s m s g e n e r a l l yh a v e l im i t e d m o b i l i t y a n d c a n n o t a v o i d t h e s e a d -v e r s e c o n d i t i o n s ( Wa ss 1 9 6 7 ) . T h i s i m m o b i l i t y isa d v a n t a g e o u s i n e n v i r o m n e n t a l a s s e s s m e n t s b e -

C o r r e s p o n d i n g a u t h o r .-~ P r e s e n t a d d r e s s : S o u t h e r n C a l i f o r n i a C o a s t a l W a t e r R e -

s e a r c h P r o g r a m , 7 1 7 1 F e n w i c k L a n e , W e s t m i n s t e r , C a l i f o r n i a9 2 6 8 3 ; t e l e 7 1 4 / 8 9 4 - 2 2 2 2 ; f a x 7 1 4 / 8 9 4 - 9 6 9 9 ; e - m a i l s t ev e w @s c c w r p . o r g .

c a u s e , u n l i k e m o s t p e l a g i c f a u n a , b e n t h i c a s s e m -b l a g e s re f l e c t l o ca l e n v i r o n m e n t a l c o n d i t i o n s( G r a y 1 9 7 9) . T h e s t r u c t u r e o f b e n t h i c a s s e m b l a g e sr e s p o n d s t o m a n y k i n d s o f st re s s b e c a u s e t h e s e a s-s e n t b l a g e s t y p i c a l ly i n c l u d e o rg a n i s m s w i t h a w i d er a n g e o f p h y si o lo g i c a l t o le r a n c e s , f e e d i n g m o d e s ,a n d t r o p h i c i n t e r a c t i o n s ( P e a r s o n a n d R o s e n b e r g1 9 78 ; R h o a d s e t al . 1 97 8 ; B o e s c h a n d R o s e n b e rg1 9 8 1 ) .

A l t h o u g h d e s c r i p t i o n s o f b e n t h i c a s s e m b l a g e sh a v e b e e n u s e fu l f o r c h a r a c t e r i z i n g e n v i r o n m e n t a lc o n d i t i o n s a n d g r a d i e n t s a t l o c a l s c a l e s , b e n t h i c a s -s e m b l a g e s h a v e n o t y e t b e e n u s e d t o t h e i r f u ll p o -t e n t i a l a s i n d i c a t o r s i n r e g i o n a l - s c a l e s t u d i e s o rs t u di e s o f e n t i r e e s t u a r ie s b e c a u s e t h e s t r u c t u r e o fb e n t h i c a s s e m b l a g e s a l s o r e f l e c t s n a t u r a l v a r i a t i o nr e l a t e d t o s a l i n i t y, s e d i m e n t t y p e , l a t i t u d e , a n dd e p t h ( B o e s c h 1 9 7 3 , 1 9 77 ; D a u e r e t a l . 19 8 4 , 1 9 8 7 ;H o l l a n d e t a l . 19 8 7 ; S c h a ff n e r e t a l . 1 98 7 ; S n e l -g r o v e a n d B u t m a n 1 99 4 : H e i p a n d C r a e y m e e r s c h1 9 9 5 ) . B e n t h i c a s s e m b l a g e s r a r e l y a r e u s e d t o as -s e s s e c o l o g i c a l c o n d i t i o n a c r o s s h a b i t a t s b e c a u s e o ft h e d i f f i c u l t y i n s e p a r a t i n g v a r i a t i o n i n t h e c o n d i -t i o n o f t h e a s s e m b l a g e c a u s e d b y h a b i t a t d if f e r -

9 1997 Estuarine Research Fe deration 14 9


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"150 S.B . Weisb0rg et al.

TABLE t_ Data sources used in developing the Chesapeake Bay B-IBI.

Number ofSampling Gear and Summer

Data .'-;oulce Time Period Samp ling Krea (rod Samples References

Chesapeake Bay Benthic 1984-1994 Petite Ponar (0.025) 1,814 Ranasinghe t al.Monitoring Program, Maryland Van Veen (0.1) (1994a)Box Corer (0.022)

Chesapeake Bay Benthic MonitoringProgram, VirginiaEPA's Environmental Monitoring andAssessment Program (EMAP)James River StudyWolf Trap

1985-1994 Box Corer (0.0184) 180 Dauer nd Alden (1995)

1990-1993 Van Veen (0.044) 293 Paul et al. (1992)1971-1972 Ponar (0.05) 28 Diaz (1989)1987-1991 Box Corer (0.063) 4 Schaffner unpublished data)

ences trom variation caused by natural and anthro-pog eni c stresses. In site-specific assessments o f ben-thic assemblages, the pro blem of accounting forhabitat-induced variation is minimized by using

nearby ref erenc e sites from the same kind of hab-itat. Benthic assessments also are used frequentlyin studies of trends, where the pr obl em of habitat-induced variat ion can be minimized by returningto the same site or area,

One appro ach used to integrate biot ic responsesand account for natural habitat variations in thefreshwater environment is to define habitat-specificreference conditions (Karr 1991; Kerans and Karr1994; DeShon 1995). This approach defines ex-pected condit ions at s ites free of anthr opog enicstress, and then assigns categorical values for vari-ous descriptive metrics by comparison with obser-vations at reference sites. The result is a multi-met-

r ic index of biot ic condit ion, f requently refer redto as an index of biotic integrity (IBI). We bor-rowed from that approach to develop a benthicindex of biotic integrity (B-IBI) for use with sum-mer estuarine benthic c ommunit ie s of ChesapeakeBay.

M e t h o d s

Macrobenthic infaunal data from five Chesa-peake Bay sampling progr ams, each of which useda 0.5-mm sieve and identified org anism s to the low-est possible taxonomic level, were used to developthe B-IBI (Table 1). Taxonomic inconsistenciesamong programs were el iminated by cross-corre-lating the species lists, identifying differences innomenclature, and consul t ing the taxonomist foreach program to resolve discrepancies. Data col-lected before 1992 were used to calibrate the in-dex; data collected between 1992 and 1994 wereused to validate the i ndex. If a sile was sam pledmore than once during a summer, which we de-fined as July 15 thro ugh Sep tem ber 30, only thefirst sample was used in the calibration dataset.

Our analytical approach was similar to the oneKarr et al. (1986) used to develop comparable in-dices for freshwater fish and involved four activi-

ties: selecting measures of benthic macroinverte-brate assemblages (referred to by Karr as metrics)that differ between references and degra ded areas;identifying quantitative thresholds that differenti-

ate between degraded and reference areas for eachselected metric; combining metric scores to devel-op an index that identifies the conditi on of theassemblage at a site; and validating the index withan independent dataset ,

Attributes of the index were selected by com-paring response of the benthic assemblage be-tween minimally affected reference sites and allother sites in our database. Reference sites wereselected from our dataset by first eliminating siteswithin highly developed watersheds and locationsnear known point-source discharges. The remain-ing sites were examined to identify those where noconta minan t excee ded Long et a l. ' s (1995) effectsrange-median (ER-M) concentrat ion, total organiccontent of the sediment was less than 2%, and dis-solved oxygen concentration was consistently high.Dissolved oxygen concentration was considered tobe consistently high if the site had no rec ord edmeas urem ent below 2 ppm, 90% of the observa-tions were above 3 ppm, and at least 80% of themeasurements were above 5 ppm. Sites for whichless than f ive independent oxygen measurementswere available were selected as reference sites onlyif they were in a region classified by the Chesa-peak e Bay Pr ogr am as bei ng fr ee of" dissolved ox-ygen stress (Magn ien et al. 1995). On e o f the sam-

pling programs (EMAP) included a 10-d, acutesediment bioassay using the amphipod Ampeliscaabdita for each site. Bioassay survival also had toexceed 80% of control survival for sites sampledby this program to be selected as reference sites.

Two criteria were used to compare metric valuesbetween reference sites and other sites in the cal-ibration dataset. First, a Mann-Whimey U-test wasused to test for differences in mean. Second, dis-t r ibut ions were compared using a Kolmogorov-Smirnov test. The latter criterion was particularlyimportant for the abundance and biomass metr ics


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Benthic Index for Chesapeake Bay 151

TABLE 2 . Mean va lues by habi ta t for each can dida te m et r ic a t re fere nce s i tes ( top numb er) and a t a ll o the r s ites (bot tom num ber) .Shadin g in the Table : Top n um ber boldface indica tes pa i r is d i ffe rent by Mann-W hi tney tes t ; bo t tom num ber boldface indica tesd i f f e r e n t b y K o l m o g o r o v - S m i r n o v te s t.N/ A = da ta unavai lab le for tha t habi ta t.

H i g h H i g h

Tidal Low Mes ohaline Meso haline Polyhaline PotvhalineFreshwate r Ol igoha l ine Mesoha l inc Sand Mud Sand Mud

Species l) iversityS h a n n o n - We i n e r

Product iv i tyA b u n d a n c e ( # m ~ )

Biom ass (g dry) (wt m -2)

1 . 8 9 2 . 4 9 2 . 4 1 3 . 3 5 2 . 8 4 4 . 0 6 3 . 5 51 . 9 0 1 . 8 4 1 . 8 4 2 . 4 4 1 . 6 6 2 . 8 8 1 . 1 0

3 , 8 4 9 2,052 1,954 2,765 1,319 4,122 2,7706 , 7 1 3 3,163 2 , 6 6 9 3 , 5 4 1 1 , 6 8 1 2 , 8 7 8 2 , 1 4 0

10.7 26.5 9.6 19.9 8 . 4 2 9 . 9 8.121.9 28.9 18.7 5 . 8 2 . 9 1 0 . 0 0 . 9

S p e c i es c o m p o s i t i o n9 Perc ent of b iom~ss as 24 .5 0 .8

pol lu t ion- indica t ive taxa N /A 1Perce nt of abun dance 29 .4 22 .4

pollutio n-indic ative taxa 45.9 27.8Percent of b iomass as 18 89.1

pol lu t ion-sens it ive taxa N /A 66 .9Per cent of abun dance 12 .8 44 .8

as pollution- sensit ive taxa 4.7 28.3

Tr o p h i c c o m p o s i t i o nPercen t of abun danc e 15.1 11 .8

as carn ivores or om nivores 10.1 15Perce nt of abun danc e 66 .6 37 .8

as deep depos i t feeders 69 .6 35.1Perc ent of abun danc e 6 .5 16 .7

as suspe nsion feed ers 11.3 13.6Percen t of abun danc e 10 .4 33 .7

as in te r face feeders 8 .4 35 .2

Depth d is t r ibut ion be low sediment -water in te r face

Perce nt of taxa 31 .4 20 .0d e e p e r t h a n 5 c m N / A 4 .2

Perce nt of taxa 8 .7 6 .7d e e p e r t h a n 1 0 c m N / A 0

Perce nt of abun danc e 11 .1 8 .6d e e p e r t h an 5 c m N / A 0 .7

P e r c e n t o f a b u n d a n c e 1 .9 1 .5d e e p e r t h a n 1 0 c m N / A 0

Perce nt of b iomass 14.1 10 .0d e e p e r t h a n 5 c m N / A 3

Perc ent of b ioma~s 3 .3 1 .7d e e p e r t h a n 1 0 c m N / A 0

0.9 2.8 9 2.3 5.98 .4 N /A 55 .4 6 .3 24 .82 . 4 11 . 6 2 6 . 5 1 2 . 1 2 2 . 9

1 9 .1 1 9 . 3 4 8 . 7 3 2 . 4 5 8 . 9

8 3 7 8 . 9 6 5 . 3 7 1 . 2 6 3 . 22 6 . 9 N / A 2 0 . l 6 6 . 1 4 0 . 4

3 0 . 6 4 0 . 3 2 9 . 5 4 8 . 5 3 9 . 925.7 2 0 . 8 1 0 . 3 2 9 . 3 8 . 4

22.9 3 7 . 4 2 3 . 1 35.3 41.818.3 23.8 15.6 32.8 19,923.8 24.3 21.4 25.1 21.421.8 21.3 18 12.4 9.4

1.2 7.0 4.8 10.6 3.18.3 15.4 6 .4 9.0 4.9

52.1 31.4 50.8 29.0 33.748.1 39.4 46.7 35.3 39.1

37.6 26.8 35.1 47.6 3 5 . 518.1 N /A 19.9 47.1 15.220.0 8.2 10.7 22.0 9.3

6.9 N /A 3.3 30.1 6.12 7 . 7 11.7 21.4 34.9 16.6

8 . 9 N / A 5 . 2 3 2 7

8.(1 2.4 5.6 16.6 4.21.1 N /A 0.8 16.3 2.4

6 8 . 8 63.6 61.6 58.3 421 7 N / A 1 1 . 5 6 8 . 5 1 7 . 4

48.3 31.6 2 9 . 9 2 8 . 5 2 4 . 93 N /A 1 33.8 10.6

b e c a u s e t h e a n t i c i p a t e d r e s p o n s e a t d e g r a d e d s i te sc o u l d b e h i g h e r o r l o w e r t h a n a t r e f e r e n c e s i t e s,d e p e n d i n g o n t h e s e v e r i t y o f t h e s tr e ss .

9 We t e s t e d 1 7 c a n d i d a t e m e t r i c s r e p r e s e n t i n gm e a s u r e s o f s p e c i e s d i ve r s it y , p r o d u c t i v i t y , s p e c i e sc o m p o s i t i o n , d e p t h d i s t r i b u t i o n , a n d t r o p h i c c o m -p o s i t i o n ( T a b l e 2 ) . T o e n s u r e t h a t t h e i n t le x w o u l db e a p p l i c a b l e t o a w i d e a r r a y o f d a ta s e t s , w e a t-t e m p t e d t o i d e n t i f y m e t r i c s t h a t h a v e b e e n s h o w nt o b e l e a s t s e n s i t i v e t o c o l l e c t i o n g e a r ( E w i n g e t a l .1 9 8 8 ) . M e t r i c s b a s e d u p o n i n d i v i d u a l s p e c i e s w e r ea v o i d e d i n f a v o r o f a s s e m b l a g e m e a s u r e s , w h i c hc a n b e e q u a l l y s e n s i t i v e t o t h e e f f e c t s o f p o l l u t i o n

b u t l e s s s e n s i t i v e t o s m a l l c h a n g e s i n h a b i t a t , s u c ha s s a l in i ty a n d s u b s t r a t e t y p e ( W a r w i c k 1 9 88 1 .

S p e c i e s w e r e c l a s s it i e d i n t o f e e d i n g g u i l d s u s i n gl i t e r a t u r e d e s c r i p t i o n s o f f e e d i n g b e h a v i o r ( J o r g e n -s e n 1 9 66 ; B o u s f i e l d 1 9 7 3 ; F a u c h a l d a n d J u m a r s1 9 7 9 ; D a u e r e t al . 1 9 8 1 ) ; a c o m p l e t e l is t o f t a x ai n c l u d e d i n e a c h g u i l d i s a v a i l a b l e i n R a n a s i n g h ee t a l. ( 1 9 9 4 b ) . I , is t s o f p o l l u t i o n - i n d i c a t i v e ( Ta b l e3 ) a n d p o l l u t i o n - s e n s i t i v e ( T a b l e 4 ) t a x a w e r e d e -v e l o p e d u s i n g a t w o - s t e p p r o c e d u r e . F i rs t , c a n d i -d a t e t a x a w e r e i d e n t i f i e d b a s e d o n k n o w n o p p o r -t u n i s t ic o r e q u i l i b r i u m l i f e - h is t o r y c h a r a c t e r i s t i c s( B o e s c h 1 9 7 3; G r a s s l e a n d G r a s s l e 1 9 7 4 ; M c C a l l


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15 2 S .B . Wei sberg e t a l .

TA B L E 3 . Ta x a d e f i n e d a s p o l l u t i o n - i n d i c a t iv e i n t h e C h e s a -p e a k e B a y B - I B I .

Anne l ida : Polychaeta

AsabeUides o culataCapitellaspp.Hypereteone heteropodaLeitoscoloplo~ fragTlisParaprionospio pinnataStreblospio benedicti

,M'thropoda : ]nsectaChironomusspp.Cladotanytarsu.~spp.Coelotanypusspp.Glyptotendipesspp.Polypedilum tripoduraProckulius subletteiTanypus spp.

Anne l ida : O l igochae ta

Aulodrilus limnobiusA ulod~ilus paucichae/aA ulodrilus p iguetiAulodrilus plurisetaBothrioneurum vqdovskyanumFIabercf . speciosu,~L~ochaetides curvosetosusIsochaetides ]reyiLimnodrilus hoffmeiste,qPotamothrix vejdovskviQuistadvilus multisetosusTubi f ic id imm atu res w i thou t

capi l l i form chaetae

Mollusca : BivalviaMulinia klteralisNucula proxima

1 9 7 7 ; R h o a d s e t a l . 1 9 7 8 ; G r a y 1 9 7 9 ; R h o a d s a n dB o y e r 1 9 8 2; Wa r w i c k 1 9 8 6; D a u e r 1 9 9 3 ). S e c o n d ,t h e li st w a s v e r i f i e d a n d a m e n d e d b y c o m p a r i n gt h e a b u n d a n c e o f e a c h t a x a a t t h e r e f e r e n c e s i te sw i t h a b u n d a n c e a t s i te s f r o m t h e c a l i b r a t i o n d a t a -s e t t h a t h a d k n o w n p o l l u t i o n s t re s s . S i te s i n t h ec a l i b r a t i o n d a t a s et w e r e c o n s i d e r e d t o b e p o l l u -t i o n -s t r es s e d if a n y s e d i m e n t c o n t a m i n a n t e x c e e d -e d t h e L o n g e t a l. (1 9 9 5 ) E R - M c o n c e n t r a t i o n a n ds u r v i v a l in s e d i m e n t t o x i c i t y te s t s w a s le s s t h a n 8 0 %o f c o n t r o l ( w h e r e t o x i c i t y d a t a w e r e a v a i l a b l e ) , o rt o t a l o r g a n i c c a r b o n i n t h e s e d i m e n t e x c e e d e d 3 % ,

o r d i s s o l v e d o x y g e n c o n t e n t w a s lo w . A s it e w as c o n -s i d e r e d t o h a v e l o w d i s s o l v e d o x y g e n i f t h e m e a -s u r e d c o n c e n t r a t i o n w a s b e l o w 0 .5 p p m o n a n y o c -c a s i o n , o r b e l o w 2 p p m o n a t l e a s t t h r e e d i f f e r e n td a t e s w i t h i n a y e a r .

M e t r i c s w e r e s e l e c t e d s e p a r a t e l y f o r e a c h o f s ev -e n h a b i t a t s ( Ta b l e 5 ) . T h e s e v e n h a b i t a t s t r a ta w e r ee s t a b l i s h e d b y c l u s t e r a n a l y s i s ( B r a y - C u r t i s s im i l a r -i ty c o e f f i c i e n t ; t l e x i b l e s o r t i n g ; 13 = - 0 . 2 5 ) o f t h ec a l i b r a t i o n d a t a s e t t o i d e n t i f y d o m i n a n t a s s e m -b l a g e s i n C h e s a p e a k e B ay , a n d b y a n al y s is o f v a ri -a n c e t o d e t e r m i n e w h e t h e r s a li n it y , g r a i n s i ze ,d e p t h , a n d l a t i t u d e d i f f e re d s i g n i f i c a n d y a m o n gg r o u p s o f s i te s d e f i n e d b y t h e d i f f e r e n t a s s e m -b l a g e s ( R a n a s i n g h e e t a l. i n p r e p a r a t i o n ) .

T h r e s h o l d s f o r th e s e l e c t e d m e t r i c s w c rc b a s e do n t h e d i s t r i b u t i o n o f v a l u e s f o r t h e m e t r i c a t t h er e f e r e n c e s it e s. T h e I B I a p p r o a c h i n v o l ve s s c o r i n ge a c h m e t r i c a s 5 , 3 , o r 1 , d e p e n d i n g o n w h e t h e ri ts v a l u e a t a s it e a p p r o x i m a t e s , d e v i a t e s s li g h t ly , o rd e v i a t e s g r e a t l y f r o m c o n d i t i o n s a t r e f e r e n c e s i te s( K a r r e t ai . 1 9 86 ) . T h r e s h o l d v a l u e s w e r e e s t a b -l i s h e d a s a p p r o x i m a t e l y t h e 5 t h a n d 5 0 t h ( m e d i a n )p e r c e n t i l e v a l u e s l o t r e f e r e n c e s i te s i n e a c h h a b i -t at . F o r e a c h m e t r i c , v a l u e s b e l o w t h e 5 t h p e r c e n -t il e w e r e s c o r e d a s 1; v a l u e s b e t w e e n t h e 5 t h a n d

TAB1.E 4. Taxa de fine d as pollution-sensitive in the Chesa-peake Bay B-IBI.

Coelen te ra ta : Anthozoa

Ceriantheopsis ame ricanu5Anne l ida : Polychaeta

Asychis elongataBhawania heterosetaChaetopterus variepedatusClymenella toruataDiopatra cupreaGlycera americanaGlycinde solitalial,oimia medusaMao'oclymer~ zonalisMarenzelleria virdisMediomastus ambisetaNephtys pictaSpiochaetopterus cos tarumSpiophanes bombyx

Arth ropodaAlpheus heterochaelisBiffarius bifo,misCallianassa setimanusCyathura politaListriella clymenellaeSquiUa empusa

Mollusca : Bivalvia

Anadara ovalisAnadara transversaCyrtopleura costataDosinia discusEnsis directusMacoma balthicaMercenarza mercenariaMya arenariaRangia cuneataSpisula solidissimaTagelus divisus"lhgelus plebeiusTellina agilis

Ech inode rma ta : Oph iu ro ideaMicrophiopholis atra

5 0 t h p e r c e n t i l e s w e r e s c o r e d a s 3, a n d v a l u e s a b o v et h e 5 0 t h p e r c e n t i l e w e r e s c o r e d a s 5. M e t r i c s c o r e sw e r e c o m b i n e d i n t o a n i n d e x by c o m p u t i n g t h em e a n s c o r e a c r o s s a ll m e t r i c s f o r w h i c h t h r e s h o l d sw e r e d e v e l o p ed . A s s e m b l a g e s w i t h a n a v e r a g e

s c o r e l es s t h a n t h r e e a r e c o n s i d e r e d s t r e s s e d , a st h e y h a v e m e t r i c v a l u e s t h a t o n a v e r a g e a r e l e s st h a n v a l u e s a t t h e p o o r e s t r e f e r e n c e s it es .

T w o o f t h e m e t r ic s , a b u n d a n c e a n d b i o m a s s , re -s p o n d b i m o d a l l y ; th a t i s, t h e r e s p o n s e c a n b e g r e a t -e r t h a n a t r e f e r e n c e s i te s w i t h m o d e r a t e d e g r e e so f s tr e s s a n d l e ss t h a n a t r e f e r e n c e s i te s w i t h h i g h e rd e g r e e s o f st re s s ( P e a r s o n a n d R o s e n b e r g 1 97 8;D a u e r a n d C o n n e r 1 9 80 ; F e r r a r o e t a l. 1 9 9 1 ). F o rt h e s e m e t r i c s , t h e s c o r i n g w as m o d i f i e d s o t h a tb o t h e x c e p t i o n a l l y h i g h ( t h o s e e x c e e d i n g t h e 9 5 t hp e r c e n t i l e a t r e f e r e n c e s i te s ) a n d l o w ( < 5 t h p e r -c e n t i l e ) r e s p o n s e s w e r e s c o r e d a s a 1 . Va l u e s b e -t w e e n t h e 5 t h a n d 2 5 th p e r c e n t i l e s o r b e t w e e n t h e

TABI,E 5. Habi ta t def ini t ions used in the Che sapeake BayB-IBI (N /A = not appl icable) .

Bottom Silt-claySalinity (-0.'5-5 N /AI.ow Me sohalin e ----5-12 N/ AHigh Mesoh al ine sand >-12-18 0-40High Mesoh al ine mu d >-12-18 >40Polyha line sand -> 18 0~,0Polyhal ine mud >- 18 >40


5/10

7 5 t h a n d 9 5 t h p e r c e n t i l e s w e r e s c o r e d a s 3 , a n dv a l u e s b e t w e e n t h e 2 5 t h a n d 7 5 t h p e r c e n t i l e s o ft h e v a l u e s a t r e f e r e n c e s i te s w e r e s c o r e d a s 5 .

T h e i n d e x w a s v a l i d a t e d b y e x a m i n i n g i ts r e -s p o n s e a t a n e w s e t o f r e f e r e n c e s it es a n d a n e ws e t o f si te s w i t h k n o w n e n v i r o n m e n t a l s tr es s. D a t au s e d f o r v a l id a t i o n w e r e c o l l e c t e d b e t w e e n 1 9 92a n d 1 9 94 a n d w e r e i n d e p e n d e n t o f d a t a u se d t oc a l i b r a te t h e i n d e x . C r i t e r i a f o r d e f i n i n g r e f e r e n c es i te s a n d k n o w n s t r e s s e d s it e s f r o m t h e v a l i d a t i o nd a t a s e t w e r e t h e s a m e a s t h o s e d e s c r i b e d f o r t h ec a l i b r a t i o n d a t a s e t .

T h e i n d e x w a s f u r t h e r v a l i d a t ed b y e x a m i n i n gt h e c o n s i s t e n c y o f t h e i n d e x r e s p o n s e a t si te s t h a tw e r e sa m p l e d m o r e t h a n o n c e d u r i n g a s u m m e r .T h i s t e s t, s u g g e s t e d b y S t e w a r t a n d L o a r ( 1 9 9 4 ) a sa p r e r e q u i s i t e f o r b i o l o g i c a l in d i c es , e x a m i n e s i n -

d e x s t a b il i t y a s s u m i n g t h a t t h e q u a l i t y o f t h e s i t es h o u l d n o t c h a n g e a p p r e c i a b l y d u r i n g t h e i n d exp e r i o d .

R e s u l t s

O n e h u n d r e d f o u r t e e n s it es f r o m t h e C h e sa -p e a k e B a y d a t a b a s e m e t o u r c r i t e r i a as r e f e r e n c es i te s f o r d e v e l o p i n g t h e B - I B I . A t l e a s t 1 0 r e f e r e n c es it e s w e r e i d e n t i f i e d f r o m e a c h h a b i t a t e x c e p t t h eo l i g o h a l i n e h a b i t a t, f o r w h i c h o n l y s e v e n r e f e r e n c es it e s w e r e a v a i l ab l e . B i o m a s s a n d d e p t h m e t r i c sc o u l d n o t b e e v a l u a t e d i n t h e t id a l f r e s h w a t e r a n dh i g h m e s o h a l i n e s a n d h ab i t a ts , t h o u g h , b e c a u s en o t a ll s a m p l i n g p r o g r a m s p a r t i t i o n e d s a m p l e s b y

d e p t h w i t h i n t h e s e d i m e n t o r m e a s u r e d b i o m a s si n d i v i d u a l l y b y t a x o n o m i c g r o u p s .

F i f t e e n o f t h e 1 7 c a n d i d a t e m e t r i c s d i f f e r e d s ig -n i f i ca n t ly i n m e a n o r i n d i s t r ib u t i o n b e t w e e n r e f -e r e n c e s i te s a n d a l l o t h e r s i t e s i n t h e c a l i b r a t i o nd a t a s e t f o r a t l e a st o n e h a b i t a t ( Ta b l e 2 ) . N o m e t r i cd i f f e r e d s i g n i f i c a n t l y in a l l s e v e n h a b i t a t s ; h o w e v e r ,f o u r m e t r i c s , s p e c i e s d i ve rs it y , a b u n d a n c e , b i o m a s sa n d p e r c e n t o f a b u n d a n c e a s p o l l ut i o n -i n d ic a t iv et a x a, d i f f e r e d i n s ix h a b i t at s . T h e n u m b e r o f m e t -r i c s t h a t d i f f e r e d s i g n i f i c a n t l y b e t w e e n r e f e r e n c es i te s a n d a l l o t h e r s i te s w a s c o n s i d e r a b l y g r e a t e r i nh i g h s a l in i t y t h a n i n l o w s a l in i t y ( Ta b l e 2 ) . F o u r -t e e n o f t h e 1 7 m e t r i c s d i f f e r e d s i g n i f i c a n t l y a t r e f -e r e n c e s it es i n p o ly h a l i n e m u d c o m p a r e d w i t h o n l yt h r e e i n t id a l f r e s h w a t e r, a n d o n e i n t h e o l i g o h a -l i n e h a b i t a t .

Ta b l e 6 l i s t s t h e s e l e c t e d m e t r i c s a n d t h e i rt h r e s h o l d s . We i n c o r p o r a t e d e a c h m e t r i c t h a t d if -f e r e d s i g n i f i c a n t l y i n s ix h a b i t a t s i n t o t h e i n d e x f o ra ll h a b it a t s b e c a u s e i n e a c h c a s e t h e d i r e c t i o n o ft h e r e s p o n s e w a s t h e s a m e i n t h e s e v e n t h h a b i t a ta n d i n m o s t c a s es t h e d i f f e r e n c e w a s s i g n i fi c a n t a ta m a r g i n a l l y l o w e r a l p h a l e v e l . We a l s o l i m i t e d t h en u m b e r o f r e d u n d a n t m e t r i c s w i t hi n a h a b i t a t t oa v o i d o v e r - w e i g h t i n g in d i v i d u a l p r o p e r t i e s o f th e

Benthic Index or Chesapeake Bay 1 5 3

a s s e m b l a g e . F o r i n s t a n c e , w e s e l e c t e d e i t h e r a b u n -d a n c e - b a s e d o r b i o m a s s - b a s e d m e t r i c s o f sp e c i e sc o m p o s i t i o n , b u t n o t b o t h . We a l so l im i t e d t h e i n -d e x t o a s i n gl e d e p t h - d i s t r i b u t i o n m e t r i c , a n d s in -g l e t r o p h i c c o m p o s i t i o n m e t r i c , w i th i n e a c h h a b i -tat .

T h e B - I B I c l a s si f i ed 9 3 % o f t h e v a l i d a t i o n s i t e sc o r r e c t l y ( Ta b l e 7 ) . T h e l o w e s t cl a s s i f ic a t i o n ef f i -c i e n c y b y h a b i t a t w a s 5 0 % i n h i g h m e s o h a l i n es a n d , b u t t h i s w a s b a s e d o n o n l y t w o sa m p l e s . C l a s-s i f i c at i o n e f f i c i e n c y w a s g e n e r a l l y p o o r e r i n l o w s a-l i ni t ie s . C u m u l a t i v e c l a s s i f ic a t i o n e f f i c i e n c y f o r h a b -i t at s w i t h s a l i n i t y le s s t h a n 1 8 % o w a s 8 4 % , w h e r e a sc l a s s if i c a t i o n e f f i c i e n c y w a s 9 7 % f o r s a l i n i t ie s a b o v e1 8 % o ( Ta b l e 7 ) .

T h e i n d e x w a s s t ab l e w i t hi n t h e s u m m e r i n d e xp e r i o d , w i t h a n o v e r a l l c o r r e l a t i o n o f 0 . 97 b e t w e e n

t h e f i r s t a n d s e c o n d s a m p l i n g v is it s t o a s i te . T h ec o r r e l a t i o n b e t w e e n t h e f ir s t a n d s e c o n d s a m p l i n gv i si ts w a s g r e a t e r t h a n 0 . 9 in a l l h a b i t a t s , a n d f o rs ix h a b i t a t s t h e c o r r e l a t i o n e x c e e d e d 0 . 95 ( Ta b l e8 ) . I n a l l h a b i t a t s e x c e p t t h e o l i g o h a l i n e a n d m e -s o h a l i n e s a n d , m o r e t h a n 8 0 % o f th e s it es s a m p l e dt w ic e d u r i n g t h e s a m e s u m m e r c l a s si f ie d t h e s a m e( Ta b l e 8 ) . M o s t o f t h e s i te s t h a t c l a s s i fi e d d i f f e r-e n t l y b e t w e e n t h e t w o v is it s w e r e s i te s f o r w h i c hi n d e x v a l u e s w e r e s i m i l a r f o r b o t h v i s i t s b u t w e r ec l o s e t o , a n d o n e i t h e r s i d e o f , t h e t h r e s h o l d v a l u eo f 3 .

D i s c u s s i o n

D e v e l o p m e n t o f t h e B - I B I w a s b a s e d u p o n q u a n -t i fy i n g e s t a b li s h e d p r i n c i p l e s o f b e n t h i c e c o lo g y,n o t o n d e v e l o p i n g n e w o n e s . T h e p r i n c i pl e s w e reb a s e d l a rg e ly o n t h e p a r a d i g m o f P e a r s o n a n d R o -s e n b e r g ( 1 9 7 8 ), w h i c h h o l d s t h a t b e n t h i c a s s e m -b l a g e s r e s p o n d t o i m p r o v e m e n t s i n h a b i t a t q ua l i tyi n t h r e e p r o g r e s s i v e s ta g es : t h e a b u n d a n c e o f o r -g a n i s m s i n c r e a s e s ; s p e c i e s d i v e r s i t y i n c r e a s e s a sn e w t a x a a r e a b l e t o s u r v i v e a t t h e s i t e ; a n d t h ed o m i n a n t s p e c i es a t t h e s it e c h a n g e f r o m p o l l u -t i o n - t o l e r a n t t o p o l l u t i o n - s e n s i t i v e s p e c i e s . I n o u rw o r k , th i s p a r a d i g m w a s s u p p l e m e n t e d w i t h a s-s u m p t i o n s t h a t t h e a b u n d a n c e a n d d i v e r si t y o f s p e-c ie s o c c u r r i n g d e e p e r i n th e s e d i m e n t s h o u l d b eg r e a t e r a t r e f e r e n c e s i t es t h a n a t d e g r a d e d s it es( Wa r w i c k 1 9 86 ; S c h a f f n e r 1 9 9 0 ; D a u e r 1 9 9 3) a n dt h a t t h e d i st r i b ut i o n o f b e n t h o s a m o n g f e e d i n gg u i l d s s h o u l d b e m o r e d i v e r se a t r e f e r e n c e s i t es( Wo r d 1 9 7 8 ) .

E a c h o f t h e s e p r i n c i p l e s w a s su c c e s s f u l a t d i s ti n -g u i s h i n g r e f e r e n c e s it es f r o m d e g r a d e d s it es w i t h i na t le a s t s o m e h a b i t a t s o f C h e s a p e a k e B a y ( Ta b l e 2 ).W h e n a p p l i e d i n d i v i d u a l l y t o t h e v a l i d a t i o n d a t a -s et , h o w e v e r , n o n e o f t h e m e t r i c s d e r i v e d f r o mt h e s e p r i n c i p l e s w e r e a s e f f e c t i v e a t d i s t i n g u i s h i n gb e t w e e n r e f e r e n c e s it es a n d d e g r a d e d s it es a s t h e


6/10


7/10

Benthic Index for Chesapeake Bay 15 5

TABI,E 7. Classification efficiency of the B- IBI for sites t-orethe val idat ion dataset.

Number of Percent CorrectlyHabita t Class Validati on Samples Classified

Tida l freshwa ter 22 86.4Oligohal ine 5 80.0Low Mesoha l ine 29 82.3High Mesoha l ine sand 2 50.0High Mesoha l ine mud 50 96.0Polyh aline sand 11 100.0Polyhal ine mu d 52 100.0

m e r o u s f o r fi sh , a r e v e r y l i m i t e d f o r b e n t h o s . T h ep o l l u t i o n t o l e r a n c e o f b e n t h o s t y p i c al l y i s c a t e g o -r i z e d b a s e d o n t h e i r l i f e - h i s to r y c h a r a c t e r i s t i c s( D a u e r 1 9 93 ) , w h i c h i n s o m e c a se s a r e a m b i g u o u so r i n c o n s i s t e n t w i t h t h e i r r e s p o n s e t o p o l l u t i o n

( S e it z a n d S c h a f f n e r 1 9 9 5 ).O n e e x a m p l e o f th i s c o n f l i c t is o u r c l a s s i f ic a t i o no f t h e c a p i t e l l i d p o l y c h a e t eMediomastus ambiseta a sa p o l l u t i o n - s e n s i t i v e t a x o n . M o s t p r e v i o u s s t u d i e sh a v e i d e n t i f i e d t h is w i d e s p r e a d s p e c i e s a s o p p o r -t u n i s t ic a n d c h a r a c t e r i s t i c o f p o l l u t i o n - s t r e s s e d s i te s( G r a s s l e a n d G r a s s l e 1 98 4 ; D a u e r 1 9 9 3 ), O u r c o m -p a r i s o n o f i ts a b u n d a n c e a t r e f e r e n c e s i te s a n d a n -t h r o p o g e n i c a l l y s t re s s e d s it es s h o w e d t h e o p p o s i t e( Ta b l e 1 0 ) . We c h o s e t o re l y o n t h e e m p i r i c a l d a t af r o m C h e s a p e a k e B a y i n d e v e l o p i n g o u r i n d e x , b u ts u g g e s t t h a t t h e c l a s s i f ic a t i o n o f t a x a i n t o s u c hg r o u p s i s a f r u i t f u l a r e a f o r c o n s i s t e n t , c o n t r o l l e de x p e r i m e n t a t i o n .

A l t h o u g h t h e p r i n c i p l e s o n w h i c h t h e B -I B I i sb a s e d w e r e e f f e c t i v e f o r d i s t i n g u i s h i n g b e t w e e ns i te s o f h i g h a n d l o w q ua l i ty , t h e y d i d n o t a p p l ye q u a l l y w e ll i n al l h a b i t a t s . T h e n u m b e r o f m e t r i c st h a t d i f f e r e d s i g n i f i c a n t l y b e t w e e n s i te s o f h i g h a n dl o w q u a l i ty i n t h e c a l i b r a t i o n d a t a s e t w a s c o n s i d -e r a b l y s m a l l e r in t h e t i d a l f r e s h w a t e r a n d o l i g o h a -l i n e h a b i t a t , a n d i n d e x v a l i d a t i o n e f f i c i e n c y w a sp r o g r e s s i v e l y w e a k e r a t l o w e r s a l i n i ti e s . F u r t h e r -m o r e , o u r v a l i d a t i o n f o r t h e t i d a l f r e s h w a t e r h a b i -t a t wa s n o t r i g o r o u s b e c a u s e o u r v a l i d a t i o n d a t a s e td i d n o t i n c l u d e a n y d e g r a d e d s i te s , a n d t h e t h r e s h -o l d v a l u e s w e i d e n t i f i e d f o r t i d a l f r e s h w a t e r w c r cl o w r e l a t iv e t o th o s e u s e d f o r t h e o t h e r h a b i t a t s .We s u g g e s t c a u t i o n i n u s i n g t h e t i d a l f r e s h w a t e rc o m p o n e n t o f t h e B - IB I u n t i l f u r t h e r v a l i d a t i o nw i th a m o r e c o m p l e t e d a t a s e t c a n b e a c c o m -p l i s h e d .

T h e l o w e r v a l i d a t i o n e f f i c ie n c y f o r t h e i n d e x a sa w h o l e a n d t h e s m a l l e r n u m b e r o f m e t r i c s t h atw o r k e d i n d i v i d u a l l y i n lo w s al i n i ti e s m a y b e d u e t ot h e i n h e r e n t l y d i f f e r e n t f a u n a t h a t i n h a b i t t h e l o ws a l in i t y h a b i t a t s ( i. e. , d o m i n a t e d b y o l i g o c h a e t e sa n d i n s e c t s i n s t e a d o f p o l y c h a e t e s , b i v a lv e s , a n dc r u s t a c e a n s ) . T h e p r i n c i p l e s o f b e n t h i c e c o l o g yu s e d t o g e n e r a t e t h e l is t o f c a n d i d a t e m e t r i c s w e re

TABI.E 8. Classification cons istency for sites visited mo re th anonce d ur ing a year.

ttabitat Class

Number ofSite-Year

Combinations Percent ofwith Multiple Sites with Correl ation

Summer Unch ange d Between RGISamples Status Values

Tida l freshwa ter 19 84.2 0.98Oligoh al ine 34 76.5 0 .97Low Me sohalin e 103 92.2 0.98High Mesohal ine sand 74 66.3 0 .95lli gh Me sohalin e mu d 61) 85.0 0.96Polyh aline sand 2 100.0 1.00Polyh aline m ud 35 97.1 0.91

b a s e d p r i m a r i l y o n s t u d i e s c o n d u c t e d i n h i g h s a li n -i ty h a b i t a t s ( e . g ., P e a r s o n a n d R o s e n b e r g 1 9 7 8)a n d m a y n o t b e e n t i r e l y a p p l i c a b l e t o t id a l f r e s h -

w a t e r b e n t h i c c o m m u n i t i e s . T h e p r i n c i p l e s d e v e l-o p e d f ox " n o n t i d a l f i ' e s h w a t e r e n v i r o n m e n t s ( K e r-a n s a n d K a r r 1 9 94 ; L e n a t a n d B a r b o u r 1 9 9 4) d i f f e rs u b s t a n t i a l l y f r o m t h o s e u s e d i n e s t u a r i e s .

O n e c o n s t r a i n t u p o n u s i n g t h e B - I B I i s t h a t i ti n c l u d e s s e v e ra l m e t r i c s t h a t w e r e n o t m e a s u r e d b ya ll b e n t h i c s a m p l i n g p r o g r a m s i n C h e s a p e a k e B ay .M a n y h i s t o r i c C h e s a p e a k e B a y c o l l e c t i o n e f f o r tsd i d n o t m e a s u r e b i o m a s s , a n d f e w o n g o i n g e f fo r t sp a r t i t i o n t h e s a m p l e s b y d e p t h , a s i s r e q u i r e d f o rm e t r i c s i n t h e h i g h e r s a l in i t y s t r at a . To m i n i m i z et h e e f f e c t o f m i s s i n g b i o m a s s d a t a , a b u n d a n c e -b a s e d s u b s t i t u t e s f o r t h e p o l l u t i o n - i n d i c a t i v e a n dp o l l u t i o n - s e n s i t i v e c a t e g o r i e s a r e g i v e n ( Ta b l e 1 1 )

b e c a u s e t h e s e m e t r i c s w e r e a l s o s i g n i l i c a n t i n al lh a b i t a ts w h e r e b i o m a s s - b a s e d m e t r i c s w e r e s e l e c t e df o r i n c l u s i o n i n t h e i n d e x . T o a s s e s s t h e e ff i~ c t o fm i s s i n g d a m o n r e l i a b i l it y o f t h e i n d e x , w e r e p e a t -e d t h e v a l i d a t i o n s t e p w i t h o u t u s i n g b i o m a s s d a t a ,d i d t h e s a m e w i t h o u t t h e d e p t h - r e l a t e d d a m , a n da g a i n w i t h o u t e i t h e r o f th e s e . O u r o v e r a l l c la s si fi -c a t i o n e f f i c i e n c y w h e n b i o m a s s m e t r i c s w e r e r e -m o v e d f e l l f r o m 9 3 % t o 9 2 % . D r o p p i n g t h e d e p t h -

TABI.E 9. Classification efficiency for each o f the metrics usedin the B-IBI based o n the val idat ion data se t . Metr ic tes t ing wasl imited to habi ta ts for which thresholds were es tabl ished.

Pc-rcent ofSitesCorrectlyClassified

Shan non- We iner diversity 89.5Abundance 82 .5Biomass 81.6Percent of abund ance as pol lu t ion- indicat ive taxa 72.1Percent of b iomass as pol lu t ion- indicat ive taxa 87.5Percent of abund ance as pol lu t ion-sensit ive taxa 90.2Percent of b iomass as pol lu t ion-sensit ive taxa 82.4Percent of abund ance as carnivores and omnivores 71.2Percent of abund ance as deep deposi t f i=eders 90.9Percent of b iomass dee per than 5 cm 90.9Percent of taxa dee per than 5 cm 65.7


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1 5 6 s . B . We i s b e r g e t a l.

TA B I .E i 0 . C o m p a r i s o n o f a b u n d a n c e a n d f r e q u e n c y o f o c c u r r e n c e o fMediomastus amtnseta a t r e f e r e n c e a n d d e g r a d e d s i te s i n al lh a b i t a t s i n w h i c h t h e y w e r e c o l l e c t e d .

Abundance (number m ~) Frequency ofOcetlrFr162(Percent of Sites)

Habitat Dataset Reference Sites Degraded S it es Rt: feren ce it es De gra de d ites

P o l y h a l i n e s a n d C a l i b r a t i o n 1 , 0 0 4 0 7 2 0P o l y h a l i n e m u d C a l i b r a t i o n 6 9 3 1 5 5 8 4H i g h M e s o h a l i n e s a n d C a l i b ra t i o n 8 4 9 2 3 5 8 4 6H i g h M e s o h a l i n e m u d C a l i b r at i o n 4 0 9 9 3 0 3

P o l y h a l i n e s a n d Va l i d a t i o n 2 , 0 7 3 0 7 7 0P o l y h a l i n e m u d Va l i d a t io n 2 , 2 8 7 7 7 7 1 1 0H i g h M e s o h a l i n e m u d Va l i d a t i o n 2 , 22 1 2 6 6 6 9

r e l a t e d m e t r i c s a l s o r e s u l t e d i n a r e d u c t i o n i n c l as -s i fi c at i o n e f fi c i e n c y f r o m 9 3 % t o 92 % . R e m o v i n gb i o m a s s a n d d e p t h - r e l a t e d m e t r i c s t o g e t h e r c a u se dn o f u r t h e r l o s s i n c l a s s i f i c a t i o n e f f i c i e n c y.

I n e x a m i n i n g t h e v a l i d a t i o n r e s u l t s , w e d i s co v -e r e d a s m a l l n u m b e r o f i n s t a n c e s i n w h i c h j u s t af e w i n d i v i d u a l s c a u s e d t h e p o l l u t i o n - s e n s i t i v e t a x am e t r i c t o b e s c o r e d a s 5 w h e n o v e r a ll a b u n d a n c ei n t h e s a m p l e w a s l o w. I n s u c h c a s es , a f e w s tr a yo r g a n i s m s c a n a r t if i c i a ll y i n f l a t e t h e r e s p o n s e . Toa v o id th is , w e r e c o m m e n d a s si g n in g a m a x i m u ms c o r e o f 3 f o r t h e p o l l u t i o n - se n s i t iv e t a x a m e t r i c i fo v e r a l l a b u n d a n c e a t t h e s it e is l e ss t h a n a t t h er e f e r e n c e s i te s ( i. e. , t h e 5 t h p e r c e n t i l e I B I a b u n -d a n c e t h r e s h o l d ) f o r th e h a b i ta t .

O u r v a l i d a t i o n t e s t s h o w e d a h i g h o v e r a l l c l as s i-f i c a ti o n e f f i ci e n cy, b u t i t d id n o t a d d r e s s w h e t h e rt h e i n d e x i s e q u a l l y s e n s it i v e t o t h e m a n y d i f f e r e n tt y p e s o f a n t h r o p o g e n i c s tr e ss o c c u r r i n g i n C h e s a -p e a k e B a y. To a s s e ss t hi s , w e r e p e a t e d t h e v a l i d a -t i o n s t e p s e p a r a t e l y f o r s e v e r a l c a t e g o r i e s o f s tr e s s,i n c l u d i n g h y p o x i a , c h e m i c a l c o n t a m i n a t i o n , a n d

TA B L E 1 1 . A b u n d a n c e - b a s e d t h r e s h o l d s t h a t m a y b e s u b s t it u t -e d f o r b i o m a s s - b a s e d t h r e s h o ld s .

.'~2o ing Criteria

5 3 1

I . o w M e s o h a l i n e

A h u n d a n c e o f p o l lu t io n -s e n s i t i v e t a x a ( % ) - > 2 5

H i g h M e s o h a l i n e m u dA b u n d a n c e o f p o l lu t i o n -

i n d i c a t i v e t a x a ( % ) --< 5A b u n d a n c e o f p o l lu t i o n -

s e n s i t i v e t a x a ( % ) - > 6 0

P o l y h a l i n e s a n d

A b u n d a n c e o f p o l lu t io n -i n d i c a t i v e t a x a ( % ) < 1 0

P o l y h a li n e m u d

A b u n d a n c e o f p o ll u t io n -i n d i c a t i v e t a x a ( % ) - < 1 5

A b u n d a n c e o f p o l lu t io n -s e n s i t i v e t a x a ( % ) - > 4 0

-5 -25 3 0

3 0 - 6 0 < 3 0

1 0 - 4 0 > 4 0

1 5 - - 5 0 > 5 0

2. .5-40


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u s e d t o d i s t in g u i s h n a t u r al f r o m a n t h r o p o g e n i cs t ress .

A l t h o u g h f a c t o r s l i k e n a t u r a l s t r e s s m u s t b e c o n -s i d e r e d i n i n t e r p r e t i n g r e s u l t s , t h e B - I B I a l l o w s sc i-e n t i st s t o a n a l y z e a n d i n t e r p r e t b e n t h i c d a t a inw a y s n o t p r e v i o u s l y p o s s i b l e b y p r o v i d i n g a u n i -f o r m s c a le f o r c o m p a r i n g t h e q u a l i ty o f t h e b e n t h i ca s s e m b l a g e a c r o ss h a b i ta t s . T h i s k i n d o f in f o r m a -t i o n c a n b e u s e d t o i d e n t if y a r e as o f t h e b a y m o s ti n n e e d o f m a n a g e m e n t a c t i o n o r to ev a lu a t e p r og -r e ss t o w a r d a se t o f e n v i r o n m e n t a l g o a l s. T h e B - I B Ii s a n e x t e n s i o n o f a n e f f o rt t o e s t a b li s h b e n t h i cr e s t o r a t i o n g o a l s f o r C h e s a p e a k e B a y ( R a n a s i n g h ee t a l. 1 9 9 4 b ) .

T h e B - I B I a l s o f a c il i ta t e s c o m m u n i c a t i o n o f c o m -p l e x b e n t h i c d a t a . M a n y t o o l s u s e d p r e v i o u s l y tos u m m a r i z e b e n t h i c d a t a , s u c h a s g r a p h i c a l m o d e l s

( Wa r w i c k 1 9 8 6 ; D a u e r 1 9 9 3 ) o r m u l t iv a r i a te t e c h -n i q u e s ( Wa r w i c k a n d C l a rk e 1 9 9 1 ; N o r r i s 1 9 9 5 ) ,a r e r o b u s t b u t r e q u i r e d e t a i l e d e x p l a n a t i o n s a n dc o m p l e x a n a ly t ic a l t e c h n i q u e s ( M c M a n u s a n d P au -l y 1 9 9 0 ) . S o m e s c i e n t is t s h a v e e x p r e s s e d c o n c e r na b o u t i n d i c es t h a t s u m m a r i z e t o o m u c h i n f o rm a -t i o n i n t o a s i n g l e n u m b e r ( E l l io t 1 9 9 4 ) . T h e s i m p l ea d d i t iv e s c a l i n g a n d e q u a l w e i g h t i n g o f m e t r i c s i nt h e B -I B I a l lo w u s e r s t o e x a m i n e i ts c o m p o n e n tp a r ts e a si l y a n d t o i d e n t if y h o w e a c h m e t r i c c o n -t r i b u t e s t o t h e o v e r a l l s c o r e . A l s o , u s e o f t h e B - I B Id o e s n o t p r e c l u d e e x a m i n i n g a n d i n t e r p r et i n g sp e -c i e s c o m p o s i t i o n d a t a , p a r t i c u l a r l y f o r si t e s c l as s i-f i e d n e a r t h e t h r e s h o l d o f 3 , if t h is is c o n s i d e r e d

n e c e s s ar y, d e s i r a b l e , o r e x p e d i e n t .

ACKNOWI.EDGMENTS

We gratefully acknowledge the contr ibuti ons of T. Morris, N.Mounfford, and A. Rodi in helping identity and resolve taxo-nomic conflicts among the many Chesapeake Bay datasets. Wethank K. Summers for access to the EMAP data, which was animportant part of our calibration and validation datasets. Wealso thank L. Scott, E Holland, M. Southerland, R. Eskin, R.Magnien, M. Luckenbach, K. Mountford, and C. DeI.isle fortheir comments on drafts of tile manuscript. Portions of thiswork were suppor ted by contrac t no. 68-D9-0166 from the l;'nit-ed States Environmental Protection Agency Chesapeake BayProgram and by contract no. CB92-006-004 from the MarylandGovern or's Council on Chesapeake Bay Research; we thank ourcontract officers, R. Batiuk and E Miller, for their assistance.

I ,ITERATURE CITE D

BILYARD, G. R. 1987. Th e value o f hent hi c inf aun a in mar in epollution m onitoring studies. Marine Pol lut ion Bullet in18:581-585.

BORSCH, D. E 1973. Classificatio n and com mun ity str uctu re ofmacrobenthos in the ttampton Roads area, Virginia. Mar ineBiology 21:226-244.

BOESCH, D. E 1977. A new look at tile z ona tio n of ben tho salong the estuar ine gradie nt, p. 245-266. hz B. C. Coull ( ed.),Ecology of Marine Benthos. University of South CarolinaPress, Columbia, South Carolina.

BOESCt[, D. E AND R. ROSENBERG. 1981. Re spon se to str ess inmarine benthic communities, p. 179-200. I n G. W. Barret and

Benthic Index for Chesapeake Bay 15 7

R. Rosenberg (eds.), Stress Effects on Natural Ecosystems.John Wiley & Sons, New York.

BOUSFIELD, E. L. 1973. Shallow-water Gamm ari dea n A mph ipo -da of New England. Cornell University Press, .Ithaca, NewYork.

COOPER, S. R_ AND G. S. BRUSH. 1993. A 2500-year hi stor y ofanoxia and eutrophication in Chesapeake Bay. Estuar ies 16:617-626.

DAUFR, D. M. 1993 . Biological criteria , envi ron men tal healt h" a n d e s t u a r in e m a c r o b e n t h i c c o m m u n i t y s t r u c t u r e . M a r in e P ol -

ht t ion Bullet in26:249-257.DAUER, D. M. AND R. W. ALDEN. 1995. Long -t er m tr en ds i n t ile

macr oben thos and water quality of the lower Chesapeake Bay(1985-1991). Marine Pol lut ion Bullet in30:840-850.

DAUER, D. M. AND W. G. CONNER. 1980. Effects of moderatesewage on benthic polychaete populations. Es tua r ine andCoastal Marine Science10:335--346.

DAUER, D. M., R. M. EWING, AND A. J. RODI, JR. 1987. Macro-benthic distribution within the s ediment along an estuarinesalinity gradien t. [nternatiouale Revue der Gesamten Hydrobiologie72:529-538.

DAUER, D. M., C. A. MAVBURY, AND R. M. EW]NG. 1981. Fe ed in gbehavior and general ecology of several spionid polychaetesfrom Chesapeake Bay. Journa l o f Expe r inwnta l Mar ine B iologyand Ecology54:21-38.

DAUER, D. M., T. I,. STOKES, R., H. R. BARKER, R., R. M. EWING,AXDJ. W. SOURBEER. 1984. Mac roh ent hic com mun iti es of thelower Chesap eake Bay. IV. Baywide tra nsects and the i nn ercontinental shelf. Internat ionale Revue der Gesamten Hydrobiologie69:1-22.

DESHON, J. E. 1995. De vel opm ent and a pplic atio n of the inver-tebrate community index, p. 217-243. I n W. P. Davis and T.P. Simon (eds.), Biological Assessmen t and Criteria. LewisPublishers, Boca Raton, Florida.

DIAZ, R.J. 1989. Pollution and tidal benth ic commun ities ofthe Jame s River Estuary, Virginia. Hydrobiologia 180:195-211.

ELLIOTT, M. 1994. The analysis of ma cro ben thi c commu nit y

data. Marine Pol lut ion Bullet in28:62-64.E~NC, R. M.,J. A. RANASINGHE, AND D. M. DAUFR. 1988. Com-parison of five benthic sampling devices. Prepared for theVirginia Water Contro l Board, Richmo nd, Virginia.

FAUCHALD, K. AND P. A. JUMARS. 1979 . T he di et of wor ms. Astudy of polychaete feeding guilds. Oceanog~'aphy and Ma rineBioloKv An nua lRev/ew 17:19.'3--284.

FFRRARO, S. P., R. C. SWARTZ, F. A. COLF, AND D. W. SCHULTS.1991. Temporal cha nges in the bentho s along a pollutiongradient: Discriminating the effects of natural phenomenafrom sewage-industrial wastewater effects. Estuar ine Coastal andShe~ Science'~3:383-407.

GRA.';SLE, J. E AND J. E GRASSI.E. 1974. Opl) or tu nist ic life his-tories and genetic systems in ma rine b enth ic polychaetes../0ur-nal o f Mar ine Research32:25.'3---284.

GRASSLE, J. E AND J. E GI~.~.SSLE. 1984. Th e uti li ty o f st ud yingthe effects of pollutants on single species populat ions in ben-thos o f mesocosms and coastal ecosystems, p. 621-642. tn H.H. White (ed.), Concepts in Marine Pollution Measurements,Maryland Sea Grant College, CoUege Park, Maryland.

GRAY, J. S. 1979. Poll uti on-i ndu ced change s in pop ulat ions.Transactions of the Royal Philosophical Society of Lon don (B)286:545-561.

GRAV, J. S., K. R. ( 'LARr~, R. M. WARUlCK, AND G. HOBBS. 1990.Detection of initial effects of pollution on marine benthos:An exam ple f rom the Ekofisk and Eldfisk oillields, North Sea.Ma rine Ecology P~'ogress Series66:285-299.

Hr.tP, C. AND J. A. CRAEVMEERSCH. 19 95 . B enth ic co mm un it ystructures in the North Sea. Helgolander Meeresuntersuchungen49:313-328.

HOLLAND, A. E, A. SIIAU(,HNF,'.kSEY, AND M. H. HEIGEX,. 1987.


10/10

1 5 8 s . B . We i s b e r g e t a l.

Long-term variation in mesohaline Chesapeake Bay benthos:Spatial and temporal patterns. Estuaries 10:227-245.

JORGENSEN, C. B. 1966. Biolog y of Sus pen sio n Feedi ng. Perga-mon Press, Oxford, England.

KARR, J. R. 1991 . Biological integrit y: A long- neg lect ed aspectof water resource management. EcologicalApplications1:66-84.

KARR, J. R., K. D. FAUSCH, P. L. ANGER.MElt-JR, e. R. YANT, AND I.J. SCHLOSSER. 1986. Assessing biological i ntegri ty in ru nn in gwaters: A method and its rationale. Special Publication 5. Il-linois Natural History Survey, Champaign, Illinois.

KERANS, B. L. ANDJ. R. KARR. 1994. A be nt hi c i nd ex of b ioti cintegrity (B-IBI) for rivers of the Tennessee Valley. EcologicalApplications4: 768-785.

I,ENAT, D. R. AND M. T. BARBOUR. 1994. Us ing b en th ic ma cro-invertebrate community structure for rapid, cost-effective, wa-ter-quality monito ring: Rapid bio asse~m ent, p. 187-216. In S .L. Loeb and A. Spacie (eds.), Biological Monito ring of Aquat-ic Systems. Lewis Publishers, Boca Raton, Florida.

LONG, E. R., D. D. McDONAI.D, S. L. SMITH, AND F. D. CAI.DER.199.5. Inc iden ce of adverse biological effects within ranges ofchemical concentrations in marine and estuarine sediments.

Environmental Management19:81-95.M.AGNIEN, R., D. BOWARD, AND S. BIEBER. 1995. Th e state of th eChesapeake Bay 1995. Report by the United States Environ-mental Protection Agency Chesapeake Bay Program, Annap-olis, Maryland.

McCAI.I., P. I.. 1977. Com mun ity pat ter ns and a daptive strate-gies of the infaunal bentho s of Long Island Sound. Journal ofMarine Research35:221-266.

McMANuS J. W. AND D. PAt: t.v. 1990. Mea sur in g ecol ogi calstress: Variations on a t he me by R. M. Warwick. Marine Biology106:305-308.

NORRIS, R. H. 1995. Biological monit orin g: The dil emn a ofdata analysis. Journal of the North American Biological .Society14:440--450.

OFFICER, C. B., R. B. BW, os, J. L. TArt ', L. E. CRONIY, M. A. TYLER,ANd W. R. BOYNTON. 1984. Ch esa pe ake Bay anoxia: Ori gin ,deve lopm ent and significance. Science 223:22-27.

PALl., J. E, K. J. SCOI'F, A. F. HOIA.AND, S. B. WEISBERG, J. K.SUMMERS, AND A. ROBERTSON. 1992. Th e es tu ar in e co mp o-nent of the U.S. EPA's Environmental Monitoring and As-sessment Program. Ctwraistry and Ecology7:93-116.

PEAR.SON, T. I t. AND R. ROSFNBI-;RG. 1978. Ma cr ob en thi c succes -sion in relation to organic enrichment and pollution of themarine environment. Oceanography and Marine Biology An nua lRev/ew 16:229-311.

RANASINGHE, J. A., L. C. S~;OTT, R. NEWPOR'r, AND S. B. WEISBFRG.1994a. Chesapeake Bay Water Quality Monito ring Program,Long-Term Benthic Monitoring and Assessment Componen t.I~evel I Comprehensive Report, July 1984--December 1993.Prepared for the Maryland Depal-tment of the Et~ironment,Baltimore, Maryland.

RANASINGHE, J. A., S. B. WEISBERG, . B. FRITHSEN, D. M. DAUER,L. C. SCHAFF'NER, AND R.J. DIAZ. 1994b. Uhe sap eak e Bay Ben-thic Community Restorati on Goals. Report CBP/TRS 107/94.

United States Environmental Protection Agency, ChesapeakeBay Program. Annapolis, Maryland.

RHOADS, D. C. AND L. F. BOYER. 19 82 . Th e ef fect s of mar in ebenthos on physical properties of sediments: A successional

perspective, p. 3-52. In P. I.. McCall and M. S. Tevesz (eds.),Animal-Sedim ent Relations. Plenum Press, New York.RHOADS, D. C., P. L. McCALL, AND J. Y. YINGST. 1978 . Distur-

bance and production on the estnarine sea floor. AmericanScientist66:577-586.

SCHAFFNER, L. C. 1990. Small-scale orga nism dist ribu tion s andpatter ns of species diversity: Evidence for positive interactio nsin an estuarine benthic community. Marine Ecology Progress Se-ries 61:107-117.

SCIIAFF'NER, L. C., R ..] . DIAZ, C. R. OI.SON, AND I. L. LAPSEN.1987. Faunal characteristics and s edim ent accumulation pro-cesses in the James River Estuary, Virginia. Estuarine Coastaland Shelf Science25:211-226.

SEn z, R. D. AND I.. C. S(2~HAFFNER. 1995. Po pu la ti on eco lo gy an dsecondary production of the polychaete Loimia medusa('Fer-ebellidae). Marine Biology121:701-711.

SNEL(,ROVE, P. V. AND C. A. BUTMA.N'. 1994. An im al -s ed im en t

relationships revisited: Cause vs. effect. Oceanography and Ma-ring Biology A n nual I~,view32:111-177.STEWART, A.J. ANDJ. M. LOAR. 1994. Spat ial a nd te mp or al vari-

ation in biological monitoring data, p. 91-124. In S. L. Loeband A. Spacie (eds.), Biological Monitoring of Aquatic Sys-tems. Lewis Publishers, Boca Raton, Florida.

TAPP, J. F., N. SHILLABEER, ANn C. M. ASHMAN. 1993. Co nt in ue dobservation of the benthic fauna of the industrialised Teesestuary, 1979-1990. Journ al of Experinwntal Marine Biology andEcology172:67-80.

WARWICK, R. M. 1986. A new m et ho d fo r de tec tin g pollu tioneffects on marine macrobenthic communities. Marine Biology92:557-562.

WARWlC;K, R. M. 1988. The level of t axon omi c disc rim inat ionrequired to detect pollution effects on marine macrobenthiccommunities. Marine Pollution Bulletin19:259-268.

WARWICK, R. M. ,tND K. R. CLARKE. 1991. A co mp ar is on of s om e

methods for analysing changes in benthi c communi ty struc-ture. Journ al of the Marine Biological Association o f the UnitedKingdom71:225--244.

Wa.,;s, M. I,. 1967. Ind icat ors of pollu tion , p. 271-183. In T. A.Olsen and E Burgess (eds.), Pollution and Marine Ecology.John Wiley and Sons, New York.

WILSON, J. G. AND D. W. JEFFRFY. 1994. Bent hi c bio log ica l pol -lution in dices in estuaries, p. 3i 1-327. InJ . M. Kramer (ed.),Biomonitoring of Coastal Waters and Estuaries. CRC Press,Boca Raton, Florida.

WORD, J. Q. 1978. The i nfauna l tro phi c index , p. 19-39. In W.Bascom (ed.), Coastal Water Research Project, Annual Reportfor the Year 1978. Southern California (:oastal Water Re-search Project, El Segunda, California.

Received for consideration, Jan uar y I I, 1995Accepted for publication, April 8, 1996

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An Estuarine Bentic Index of Biotic Integrity IBI