Do Not Remove f rom the Library U. S. Fish and Wild!ife Ser%/Jce - l m .

FWSlOBS-82111.19 i ~ a t ~ o n a I .-C>=~-~I I-,' 1 ~ b r l L ~ l

700 Caiun Dome Bou!evard TR EL-82-4

March 1 9 8 4

Species Profiles: Life H~Mw~%& uisiana 70506

Environmental Requirements of Coastal Fishes and Invertebrates (South Atlantic)

BLUE CRAB

Coastal Ecology Group Fish and Wildlife Service Waterways Experiment Station U.S. Department of the Interior U.S. Army Corps of Engineers

FWS/OBS-82/11.19 TR EL-82-4 March 1984

Species P r o f i l e s : L i f e H i s t o r i e s and Envi ronmenta l Requirements o f Coasta l F ishes and I n v e r t e b r a t e s (South A t l a n t i c )

BLUE CRAB

by

Michael J. Van Den Avy le and

Dean L. Fowler Georgia Cooperat ive F i she ry Research U n i t

School o f Fo res t Resources U n i v e r s i t y o f Georgia

Athens, GA 30602

P r o j e c t Manager L a r r y Shanks

P r o j e c t O f f i c e r Norman Benson

Na t i ona l Coasta l Ecosystems Team U. S. F i s h and W i l d l i f e Se rv i ce

1010 Gause Boulevard S l i d e l l , LA 70458

Performed f o r Coasta l Ecology Group

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

Vicksburg, MS 39180

and

Na t i ona l Coasta l Ecosystems Team D i v i s i o n o f B i o l o g i c a l Serv ices

Research and Development F i s h and Wi ld1 i f e Se rv i ce

U.S. Department o f t h e I n t e r i o r Washington, DC 20240

This series should be referenced as follows:

U.S. Fish and Wildlife Service. 1983-. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates. U.S. Fish Wi ldl . Serv. FWS/OBS-82/11. U.S. Army Corps of Engineers, TR EL-82-4.

This profile should be cited as follows:

Van Den Avyle, M. J. 1984. Species profiles: 1 ife histories and environmental requirements of coastal fishes and invertebrates (South Atlantic) - - blue crab. U.S. Fish Wildl. Serv. FWS/OBS-82/11.19. U.S. Army Corps of Engineers, TR EL-82-4. 16 pp.

PREFACE

Th i s spec ies p r o f i l e i s one o f a s e r i e s on coas ta l aqua t i c organisms, p r i n c i p a l l y f i s h , o f spor t , commercial, o r e c o l o g i c a l importance. The p r o f i l e s a re designed t o p rov i de coas ta l managers, engineers, and b i o l o g i s t ; w i t h a b r i e f comprehensive ske tch o f t he 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 env i ronmental requ i r e - ments o f t h e spec ies and t o desc r i be hoir popu la t i ons of t h e spec ies may be expected t o r e a c t t o env i ronmenta l changes caused by coas ta l development. Each p r o f i l e has sec t i ons on taxonomy, 1 i f e h i s t o r y , e c o l o g i c a l r o l e , env i ronmenta l r equ i rements, and economic importance, i f apol i c a b l e. A t h r e e - r i n g b i n d e 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 t hey a r e prepared. T h i s p r o j e c t i s j o i n t l y planned and f inanced by t h e 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 Serv ice.

Suggest ions o r ques t ions r ega rd i ng t h i s r e p o r t should be d i r e c t e d t o :

I n f o r m a t i o n T r a n s f e r S p e c i a l i s t Na t i ona l Coasta l Ecosystems Team U.S. F i s h and W i l d l i f e Se rv i ce NASA-Sl i d e l 1 Computer Complex 1010 Gause Boul evard Sl i d e l 1, LA 70458

U.S. Army Engineer Waterways Experiment S t a t i o n A t t e n t i o n : WESER Pos t O f f i c e Box 631 Vicksburg, MS 39180

CONTENTS

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii CONVERSIONTABLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v i

NOMENCLATURE /TAXONOMY /RANGE . . . . . . . . . . . . . . . . . . . . . . . . 1 MORPHOLOGY/IDENTIFICATION A I D S . . . . . . . . . . . . . . . . . . . . . . 3 REASON FOR INCLUSION I N S E R I E S . . . . . . . . . . . . . . . . . . . . . . 3

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L I F E HISTORY 3 S p a w n i n g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 D e v e l o p m e n t . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 E g g s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . L a r v a e 5 J u v e n i l e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A d u l t s 5 M i g r a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

GROWTHAND MOLT INGCHARACTERIST ICS . . . . . . . . . . . . . . . . . . . . 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . THE FISHERY 7

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ECOLOGICALROLE 9 ENVIRONMENTAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . 10

T e m p e r a t u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 S a l i n i t y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 H a b i t a t S t r u c t u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 O t h e r E n v i r o n m e n t a l F a c t o r s . . . . . . . . . . . . . . . . . . . . . . . 12

LITERATURE C I T E D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 3

CONVERSION FACTORS

M e t r i c t o U.S. Customary --- To Obta in --

mi 11 ime te r s (mm) cen t ime te r s (cm) meters (m) k i l omete rs (km)

inches inches f e e t m i l e s

square meters (m2) square k i l o m e t e r s (km') hec ta res (ha)

square f e e t square m i l e s ac res

l i t e r s (1) cub i c meters (m3) cub i c meters

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

mi 11 i grams (mg) grams (g ) k i lograms (kg) m e t r i c t ons (mt) m e t r i c t ons k i l o c a l o r i e s ( kca l )

ounces ounces pounds pounds s h o r t t ons BTU

Cel s i us degrees Fahrenhe i t degrees

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

inches inches f e e t ( f t ) f a thorns m i l e s (mi ) n a u t i c a l m i l e s (nmi )

mi 1 1 imete rs cen t ime te r s mete rs mete rs k i l o m e t e r s k i l o m e t e r s

square f e e t ( f t 2 ,

acres square m i l e s (mi2)

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

ga l 1 ons ( ga l ) cub i c f e e t ( f t 3 ) a c r e - f e e t

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

ounces (oz) pounds ( I b ) s h o r t tons ( t o n ) BTU

grams k i 1 ograms m e t r i c tons k i l o c a l o r i e s

Fahrenhe i t degrees Cel s i u s degrees

ACKNOWLEDGMENTS

We a r e g r a t e f u l f o r rev iews by Dr. Mac Rawson, Georgia Cooperat ive Mar ine Ex tens ion Serv ice , Brunswick, and Dr. Kenneth Tenore, Skidaway I n s t i t u t e o f Oceanography, Savannah, GA.

F i g u r e 1. Blue c r a b .

B L U E CRAB

S c i e n t i f i c name . . C a l l i n e c t e s s a p i d u s (Rathbun)

P r e f e r r e d common name . . . . Blue c r a b ( F i g u r e 1 )

O t h e r common names. . . . E d i b l e c r a b , c r a b ; young f e m a l e s a r e c a l l e d s a l l y c r a b s ; a d u l t f e m a l e s a r e c a l l e d s o o k s ; and males a r e c a l l e d j immies , jimmy-dicks , o r c h a n n e l e r s (Van Engel 1958)

C l a s s . . . . . . . . . . . . C r u s t a c e a Order . . . . . . . . . . . . Decapoda

Family . . . . . . . . . . P o r t u n i d a e Geographic r ange : C o a s t a l w a t e r s ,

p r i m a r i l y bays and b r a c k i s h e s t u a r i e s from M a s s a c h u s e t t s Bay, southward t o t h e e a s t e r n c o a s t o f Sou th America , i n c l u d i n g t h e Gulf o f Mexico. The b l u e c r a b o c c u r s i n c o a s t a l w a t e r s t h r o u g h o u t t h e South A t l a n t i c B i g h t ( F i g u r e 2 ) . I t has a l s o been r e p o r t e d from F r a n c e , Hol l and , Denmark, and t h e e a s t c o a s t o f t h e Medi te r ranean Sea ( C h u r c h i l l 1921; Van Engel 1958) .

ATLANTIC OCEAN

M I L E S

K I L O M E T E R S

Coastal distribution

Major commercial fishery CKSONVILLE in the South Atlantic bight

F igu re 2. D i s t r i b u t i o n o f the b l u e c rab i n t he South A t l a n t i c B i g h t , south- eas te rn Un i t ed S ta tes . The Pam1 i c o Sound area i n No r th Ca ro l i na suppor ts t he ma jo r commercial f i s h e r y i n t he South A t l a n t i c B igh t .

2

MORPHOLOGY / IDENTIFICATION AIDS

The b l u e c rab i s g r a y i s h o r b l u i s h green w i t h r e d on carapace spines (Py le and Cronin 1950; W i l l i ams 1965). Males have b l u e p inchers on chel ipeds; mature females have red p i nchers on chel i peds. Underparts a re o f f - w h i t e w i t h t i n t s of y e l l o w and p i n k (W i l l i ams 1965). Young crabs o f t e n a r e brownish w i t h conspicu- ous w h i t e markings (Newcombe 1945).

The carapace, i n c l u d i n g l a t e r a l spines, u s u a l l y 2.5 t imes as wide as long, moderate ly convex, and n e a r l y smooth except f o r smal l t u b e r c l e s t h a t occur on i n n e r b ranch ia l and c a r d i a c regions. The a n t e r i o r margin o f t h e carapace has a median o r f r o n t a l r e g i o n t h a t extends between t h e compound eyes, and two l a t e r a l reg ions. The median reg ion has f o u r s e r r a t i o n s and each l a t e r a l r e g i o n has e i g h t (F igu re 1 ) ; t h e number o f s e r r a t i o n s i s cons tan t f o r t h i s species.

The abdomen o f t h e male i s shaped l i k e an i n v e r t e d 'IT" (F igu re 3) . The abdomen o f immature females i s t r i a n g u - l a r , and t h e mature female has a broad, rounded abdomen t h a t i s f o l d e d l o o s e l y aga ins t t h e v e n t r a l s i d e o f t h e t h o r a c i c s te rna (F igu re 3).

REASON FOR INCLUSION IN SERIES

The b l u e c rab suppor ts a va luab le commercial f i s h e r y th roughout t h e South A t l a n t i c S ta tes and a long most o f t h e

B@

. ,.. - . . -: , I... ..._ ' . I

F igu re 3. Ven t ra l view o f t h e b l u e crab male (A), immature female (B) , and mature female (C) ( T r u i t t 1939).

eas te rn coas t of t h e U n i t e d States. Es tua r i es a r e e s s e n t i a l i n t h e l i f e h i s t o r y of t h e b l u e crab; t h e spec ies ' h i g h abundance i n e s t u a r i e s and i t s omnivorous f eed ing h a b i t s suggest t h a t t h e b l u e c rab p l a y s an impo r tan t r o l e i n t h e s t r u c t u r e and f u n c t i o n o f e s t u a r i n e communities. Dur ing p re- a d u l t stages o f l i f e , t h e b l u e c rab i s eaten by a l a r g e number o f e s t u a r i n e and mar ine animals.

LIFE HISTORY

Spawn i n g

B lue c rabs mate i n Chesapeake Bay f rom May th rough October (Van Engel 1958; W i 11 i ams 1965) and th roughout t h e y e a r i n t h e St . Johns R iver , F l o r i d a (Tagatz 1968). Mat ing p r imar - i l y occurs i n r e l a t i v e l y l o w - s a l i n i t y waters i n upper areas o f e s t u a r i e s and i n lower p o r t i o n s of r i v e r s (Py le and Cron in 1950; Darnel 1 1959; W i l l iams 1965; Tagatz 1968).

W i l l iams (1965) descr ibed t h e b l u e c rab1 s mat ing behavior . Males may mate d u r i n g t h r e e o r four i n t e r - m o l t phases a f t e r they mature. Females mate o n l y once i n t h e i r l i v e s , b u t t h e sperm f rom t h i s mat ing i s s t o r e d i n seminal r ecep tac les and may be used as o f t en as t h e female spawns, g e n e r a l l y two o r more t imes d u r i n g a 1- o r 2-year p e r i o d (Py le and Cronin 1950; Van Engel 1958; W i l l i ams 1965).

A f t e r mat ing, females m ig ra te t o h i gh -sa l i n i t y waters i n lower es tua r - i e s , sounds, and nearshore spawning areas (Churchi 11 1921; Darnel 1 1959; F i s c h l e r and Walburg 1962). Most females spawn f o r t h e f i r s t t ime 2 t o 9 months a f t e r mat ing ( C h u r c h i l l 1921; W i l l i ams 1965). I n Chesapeake Bay, females remain i n t h e lower es tua r i es and spawn t h e f o l l o w i n g s p r i n g o r summer (Churchi 11 1921). I n F lo r i da , Tagatz (1968) found t h a t females which mated i n t h e s p r i n g o r sumner f i r s t spawned 1 o r 2 months l a t e r i n t he same year , w i t h peak spawning from

October th rough December. S tee le (1979) r e p o r t e d spawning i n F l o r i d a f rom March through December when wate r temperatures exceeded 22°C. Crabs t h a t mated d u r i n g t h e f a l l o r w i n t e r i n t h e St . Johns R i ve r spawned f rom March th rough June o f t h e n e x t year . Some females may spawn t w i c e d u r i n g a s i n g l e season (Tagatz 1968).

A comparison o f mat ing and spawn- i n g c h a r a c t e r i s t i c s r e p o r t e d f o r t h e St . Johns R i v e r and Chesapeake Bay suggests t h a t as temperatures i nc rease i n t h e s o u t h e r l y d i r e c t i o n , mat ing and spawning seasons become l o n g e r and l e s s d i s t i n c t . T h i s f a c t i s p robab l y due t o more r a p i d growth and m a t u r a t i o n a t warmer temperatures. Daugherty (1952) found t h a t t h e spawning season was s i g n i f i c a n t l y s h o r t e r d u r i n g yea rs i n which temperatures were low f o r extended per iods .

The female ex t rudes f e r t i l i z e d eggs i n t o a mass o r "sponge" t h a t remains a t tached t o h a i r 1 i ke branches ( se tae ) o f t h e appendages o f t h e abdomen u n t i 1 l a r v a e emerge (Churchi 11 1921; Newcombe 1945; Py le and Cron in 1950). Formation o f t h e sponge, which may c o n t a i n 700,000 - 2,000,000 eggs, takes about 2 h r ( C h u r c h i l l 1921; T r u i t t 1939; W i l l i ams 1965). The presence o f empty egg cases on swim- merets o r t h e occurrence o f l a r g e , b r i gh t - red a d u l t nemertean worms ( ~ a r c i n o n e m e r t e s c o r c i n o p h i l a ) on t h e a i l l s o f a mature female i n d i c a t e t h a t t h e i n d i v i d u a l has spawned a t l e a s t once (Churchi 11 1921; Hopkins 1947).

Development

Growth and development o f t h e b l u e crab, as w i t h o t h e r crustaceans, c o n s i s t o f a s e r i e s o f l a r v a l , j u v e n i l e , and a d u l t stages d u r i n g which a v a r i e t y o f morpho log ica l , behav io ra l , and p h y s i o l o g i c a l changes occur . These changes a re most d ramat ic when t h e animal mo l ts , o r sheds i t s r i g i d exoskeleton, p e r m i t t i n g growth and changes i n body shape. P r i o r t o m o l t - i ng , a new s h e l l i s formed beneath t h e

o l d exoskeleton, which i s then l oos - ened and c a s t o f f . The new s h e l l i s i n i t i a l l y s o f t , b u t i t expands and hardens i n a few hours. The stage between m o l t s i s termed " i n t e r m o l t."

The number of m o l t s d u r i n g c e r t a i n l i f e s tages (e.g., l a r v a l and j u v e n i l e ) i s r e l a t i v e l y u n i f o r m among crabs, b u t t h e r a t e o f m o l t i n g (and hence g rowth) can va ry cons ide rab l y and i s a f fec ted by many envi ronmenta l f a c t o r s . Much o f t h e i n f o r m a t i o n summarized below was ob ta i ned f rom comprehensive s t u d i e s o f b l u e c rab i n t h e Chesapeake Bay area ( C h u r c h i l l 1921; Newcombe 1945; Van Engel 1958) and t h e St. Johns R i v e r Estuary i n F l o r i d a (Tagatz 1968). I n f o r m a t i o n on t h e l i f e s tages o f t h e c rab i n these areas shoul d be r e p r e s e n t a t i v e th roughout t h e spec ies ' range. Rates o f development and t i m i n g o f c e r t a i n impo r tan t events (such as mating, spawning, and m i g r a t i o n s ) th roughout most o f t h e South A t l a n t i c B i g h t w i l l genera l l y be i n t e r m e d i a t e between r e s u l t s p resen ted f o r t h e two areas. Documented v a r i a t i o n s a r e emphasized and c i t e d below.

Eggs

When f i r s t deposi ted, t h e eggs a r e b r i g h t orange; b u t t hey become y e l l o w , brown, and then dark brown b e f o r e ha t ch ing (Van Engel 1958). The c o l o r change i s caused by abso rp t i on o f t h e y e l l o w y o l k and development o f dark pigment i n t h e eyes. Eggs a r e about 0.25 mm i n d iameter ( C h u r c h i l l 1921), and i n c u b a t i o n genera l l y r e q u i r e s 1 t o 2 weeks. Sandoz and Rogers (1944) r e p o r t e d t h a t ha t ch ing o f b l u e crab eggs must occur a t s a l i - n i t i e s of 23 t o 33 p p t and tempera- t u r e s of 19" t o 29" C. M o r t a l i t y o f eggs has been a t t r i b u t e d t o fungus, p reda t i on , s u f f o c a t i o n i n s tagnant water , and extreme temperatures (Couch 1942; Humes 1942; Rogers-Tolber t 1948). On t h e average, o n l y one o u t o f every m i l l i o n eggs su rv i ves t o become a mature a d u l t (Van Engel 1958).

Larvae J u v e n i l e s

F i r s t s t a g e l a r v a e , c a l l e d zoeae , measure approx imate ly 0.25 mm a t ha tch- i n g . They b e a r l i t t l e morphological resemblance t o a d u l t s (Hopkins 1 9 4 3 ) , a r e f i l t e r f e e d e r s , and l i v e a plank- t o n i c e x i s t e n c e i n t h e h i g h - s a l i n i t y s u r f a c e w a t e r s n e a r t h e spawning grounds ( P y l e and Cronin 1950; Darnel1 1959). Tagatz (1968) found more zoeae n e a r t h e w a t e r ' s s u r f a c e t h a n a t t h e bottom. Churchi 11 (1942) p rov ided i l l u s t r a t e d d e s c r i p t i o n s of zoeae morphology.

The zoeae and a l l subsequent 1 i f e s t a g e s can i n c r e a s e body s i z e on ly by mol t ing (Hay 1905; Py le and Cronin 1950) . Zoeal development may r e q u i r e 31 t o 49 days , depending on s a l i n i t y and t e m p e r a t u r e , b u t development t ime has been shown t o be v a r i a b l e even i n a s i n g l e s a l i n i ty - tempera ture regime (Wil l iams 1965) . Zoeae molt f o u r t o seven t imes b e f o r e e n t e r i n g t h e n e x t s t a g e of development, and i t has been hypothesized t h a t t h e number o f m o l t s r e q u i r e d t o reach t h e megalops s t a g e depends on tempera ture and s a l i n i t y . The f i n a l zoeal s t a g e i s about 1.0 mm i n width (Hopkins 1943; Sandoz and Rogers 1944) .

The f i n a l molt of t h e zoeae i s c h a r a c t e r i z e d by a conspicuous change t o t h e second l a r v a l s t a g e , c a l l e d a mega1 ops (a1 s o termed megalopa [ s i n g . ] o r megalopae [ p l . ] ) . The megalops l a r v a i s more crab1 i ke i n appearance t h a n t h e zoeae , i s broader i n r e l a t i o n t o i t s l e n g t h , and h a s b i t i n g c laws and p o i n t e d j o i n t s a t t h e ends o f t h e l e g s ( s e e Churchi 11 [ I9211 and Newcombe [I9451 f o r i l l u s t r a t i o n s ) . I t measures about 1 .0 mm i n width. The megalops swims f r e e l y , b u t g e n e r a l l y s t a y s n e a r t h e bottom i n n e a r s h o r e o r lower- e s t u a r i n e , h igh-sa l i n i t y a r e a s (Tagatz 1968) . The megalops s t a g e l a s t s 6 t o 20 days , a f t e r which t h e megalops m o l t s i n t o t h e " f i r s t c rab" s t a g e , wi th p r o p o r t i o n s and appearance more 1 i ke t h o s e o f an a d u l t .

The j u v e n i l e " f i r s t c rab" i s t y p i c a l l y 2.5 mm wide (f rom t i p t o t i p of t h e l a t e r a l s p i n e s of t h e c a r a p a c e ) . These juven i 1 e s g radua l 1 y m i g r a t e i n t o s h a l l o w e r , l e s s - s a l i n e w a t e r s i n upper e s t u a r i e s and r i v e r s where t h e y grow and mature ( F i s c h l e r and Walburg 1962) . Van Engel (1958) and Tagatz (1968) r e p o r t e d t h a t many j u v e n i l e s had completed t h i s m i g r a t i o n by f a l l and e a r l y w i n t e r . Males g e n e r a l l y m i g r a t e f a r t h e r upstream, p r e f e r r i n g low-sal i n i t y w a t e r s , whereas females t end t o s t a y i n lower r i v e r s and e s t u a r i e s (Dudley and Judy 1971; Music 1979) .

Growth and m a t u r a t i o n occur d u r i n g a s e r i e s o f mol t s and i n t e r m o l t phases , each o f which i s termed a "c rab" s t a g e a c c o r d i n g t o t h e number of mol t s t h a t have o c c u r r e d s i n c e t h e mega1 ops s t a g e . Churchi 11 (1921) r e p o r t e d t h a t j u v e n i l e s reached t h e 9 t h o r 1 0 t h c r a b s t a g e by October i n Chesapeake Bay, b u t growth v a r i e s c o n s i d e r a b l y among y e a r s and wi th l a t i t u d e a l o n g t h e A t l a n t i c c o a s t . Molting and growth s t o p d u r i n g w i n t e r ( C h u r c h i l l 1921; Darnel 1 1959) ; growth resumes a s w a t e r s warm, and j u v e n i l e s g e n e r a l l y reach m a t u r i t y d u r i n g t h e s p r i n g o r summer of t h e y e a r fo l lowing t h e i r ha tch ing .

Adul t s

Sexual m a t u r i t y i s reached a f t e r 18-20 p o s t l a r v a l mol t s a t 1 t o 1 .5 y e a r s o f age i n Chesapeake Bay (Wil l iams 1965; Van Engel 1958) . S i z e a t m a t u r i t y i s v a r i a b l e ; s e x u a l l y mature females a s smal l a s 51 mm ( c a r a p a c e w i d t h ) have been r e p o r t e d i n South Carol i na (F i s c h l e r and Wal burg 1962) , b u t Tagatz (1968) found imma- t u r e females a s l a r g e a s 177 mm i n wid th i n F l o r i d a . Males c o n t i n u e t o grow and mol t a f t e r r e a c h i n g sexual m a t u r i t y ; b u t a f t e r females mature , t h e y mate and do n o t molt o r grow a g a i n .

Af ter mature females mate and migra te t o spawning areas, they remain there o r move on ly a s h o r t d is tance out t o sea dur ing the remainder o f t h e i r l i v e s (Wi l l ianls 1965). I n warmer months, males genera l l y remain i n low- s a l i n i t y waters such ar creeks, r i v e r s , and upper es tuar ies (Churchi 11 1921; Van Engel 1958; Dudley and Judy 1971; Music 1979). The maximum age f o r most b lue crabs i n Chesapeake Bay (Church i l l 1921) and North and South Caro l ina (Wi l l iams 1965) i s about 3 years. Tagatz (1968) repor ted t h a t t he maximum age i n the St. Johns River was 4 years. Hay (1905) and T r u i t t (1939) repor ted t h a t adu l t s l i v e d an average o f l e s s than 1 year a f t e r reaching ma tu r i t y .

/ M igra t ions

Adu l t b lue crabs are e x c e l l e n t swimmers and a l so can move q u i c k l y on land (Py le and Cronin 1950). Tagging s tud ies along the South A t l a n t i c have shown t h a t b lue crabs r a r e l y move from one es tua r ine system t o another (Po r te r 1956; Cargo 1958; F i s c h l e r and Walburg 1962; Judy and Dudley 1970). These s tud ies a l s o showed t h a t most crabs l eav ing an estuary genera l l y remain i n adjacent coasta l areas, b u t tagged female crabs have occas iona l ly been recovered 100-540 km from t h e i r re lease s i t e s . Such long-range movements genera l l y occur a f t e r mating and p r i o r t o spawning. Crabs along t h e F l o r i d a gu1 f coast undergo more extensive migra t ions between es tua r ies than do crabs along the South A t l a n t i c B igh t (S tee le 1979). Males undergo l e s s extensive migra t ions than females.

Migra t ions o f b lue crabs w i t h i n es tuar ine systems are r e l a t e d t o phases o f t h e i r 1 i f e cycle, season, and, t o a l e s s e r extent , searches f o r favorab le environmental cond i t i ons (Church i l l 1921; F i e d l e r 1930; T r u i t t 1939; F i s c h l e r and Walburg 1962). Most b l u e crabs move t o r e l a t i v e l y deeper, warmer waters dur ing w i n t e r and r e t u r n t o r i v e r s , t i d a l creeks, s a l t marshes, and sounds when cond i t i ons become more favorab le i n the spr ing (L i v ings ton

1976; Subrahmanyam and Coul t a s 1980). L i v ings ton (1976) repor ted t h a t crabs i n a F l o r i d a es tuary moved from inshore areas t o deeper, more s a l i n e waters when shal low waters cooled.

Migra t ions associated w i t h reproduct ive cycles o r maturat ion are descr ibed i n the Spawning and Develop- ment sect ions,

GROWTH AND MOLTING CHARACTERISTICS

From the f i r s t crab stage t o the adu l t , successive in termol t stages o f t he crab a re morpho log ica l ly s i m i l a r except f o r s ize. Growth ra tes vary among i n d i v i d u a l s and a re a f fec ted by temperature, s a l i n i t y , and many o t h e r fac to rs . Hence, i t i s genera l l y no t poss ib le t o determine t h e stage t h a t a p a r t i c u l a r crab i s i n from i t s s i z e o r ex te rna l c h a r a c t e r i s t i c s (Church i l l 1921). Migra t ions and movements w i t h i n es tua r ies f u r t h e r complicate es t ima t ion o f growth ra tes , and repeated sampl i ng a t one 1 o c a t i on can lead t o erroneous conclusions (Darnel 1 1959; Adkins 1972; Palmer 1974). Thus, t he growth and mo l t i ng pa t te rns presented here were der ived i n p a r t from labo ra to ry studies. Th is summary should have general a p p l i c a b i l i t y throughout the South A t l a n t i c Bight , bu t ra tes o f growth w i l l vary consid- e rab ly w i t h temperature, sa1 i n i t y , and o t h e r s i te-speci f i c f ac to rs .

Small crabs mo l t f requent ly , and the t ime between mol ts increases as crabs grow l a r g e r (Van Engel 1958). A t each normal molt, carapace wid th t y p i c a l l y increases 25%-40% (Churchi 11 1921; Gray and Newcombe 1939; Van Engel 1958). Resul ts o f C h u r c h i l l ' s (1921) l abo ra to ry s tud ies on growth o f Chesapeake Bay b lue crabs serve as a general g u i d e l i n e f o r growth pa t te rns o f b lue crabs i n V i r g i n i a and adjacent States (Table 1). The increase i n s i z e associated w i t h s p e c i f i c mol ts may be g e n e t i c a l l y c o n t r o l l e d , b u t i t i s be l ieved t h a t environmental cond i t i ons have a

Table 1. Growth o f b l u e crabs a t temperatures and s a l i n i t i e s t y p i c a l of Chesapeake Bay ( C h u r c h i l l 1921).

L i f e s tage Carapace w i d t h Inc rease i n w i d t h M o l t i n t e r v a l Age (mm) (mm (days) (days)

Mega1 ops 1 s t c rab 2nd c rab 3 r d c rab 4 t h crab 5 th c rab 6 t h c rab 7 t h c rab 8 t h c rab 9 th c rab

10 th c rab 11 th crab 12th c rab 13th c rab 14 th c rab 15 th c rab

g r e a t e r i n f l uence . Unfavorable water c o n d i t i o n s , inadequate food, o r i n j u r i e s such as t h e l o s s o f one o r more l e g s may cause sma l l e r inc reases i n s i z e o r no growth f o l l o w i n g a m o l t (Van Engel 1958). Tagatz (1968) found t h a t j u v e n i l e crabs i n no r theas te rn F l o r i d a e x h i b i t e d more growth p e r m o l t i n h i ghe r s a l i n i t y waters.

Van Engel (1958) repo r ted t h a t crabs hatched i n l a t e May i n Chesapeake Bay grew t o 64 mm i n w i d t h by November and t o 127 mm by t h e f o l l o w i n g August. I n t h e St. Johns R iver , most b l u e crabs reach harves t - a b l e s i z e (127 mm) 1 y e a r a f t e r hatch- i ng . Average s i z e a t m a t u r i t y has been repo r ted t o be about 178 mm i n Chesapeake Bay (Churchi 11 1921), 203 mnl i n t h e Caro l inas (W i l l i ams 1965), and 102-178 mm i n t h e St . Johns R i ve r (Tagatz 1968). The 1 i t e r a t u r e i n d i c a t e s cons iderab le v a r i a t i o n i n t h e age a t which sexual m a t u r i t y i s reached: 12-18 months i n Chesapeake Bay (Newcombe 1945; Van Engel 1958), about 22 months i n South Ca ro l i na

( F i s c h l e r and Walburg 1962), and l e s s than 12 months i n t h e St. Johns R i v e r (Tagatz 1968). There i s cons iderab le ove r l ap i n s i z e ranges o f immature and mature c rabs (Tagatz 1968).

THE FISHERY

The b l u e crab suppor ts t h e l a r g e s t c rab f i s h e r y i n t h e Un i t ed S ta tes . Annual commercial l and ings i n t h e South A t l a n t i c averaged about 48 m i l l i o n 1b (va lued a t $9 m i l l i o n ) f o r 1977-81 ( B e l l 1978; Na t i ona l Mar ine F i s h e r i e s Se rv i ce [NMFS] 1981a, 1982). Sho la r (1979) summarized most aspects o f t h e A t l a n t i c b l u e c rab f i s h e r y , and i n c l u d e d land ings , by S ta te , f o r 1950- 77. Tagatz and H a l l (1971) p rov ided an annotated b i b l i o g r a p h y on t he f i s h i n g i n d u s t r y and b i o l o g y o f t h e b l u e crab.

Harvest f rom t h e South A t l a n t i c B i g h t du r i ng 1977-81 represented 25% - 33% o f t h e t o t a l U. S. commercial b l ue c rab harves t . Landings i n t he South

A t l a n t i c g e n e r a l l y c o n s i s t of about 50% from No r th Ca ro l i na , 20%-25% f rom Georgia, 20% f rom South Ca ro l i na , and 7%-10% f rom F l o r i d a (NMFS 1979, 1980a, 1980b, 1981b). Nor th C a r o l i n a ' s Pamlico Sound y i e l d e d about 10 m i l l i o n 1b annua l l y f rom 1970 t o 1978 and i s t h e ma jo r p roduc t i on area o f t h e South A t l a n t i c (Sho la r 1979). Catches a l ong t h e eas t coas t of F l o r i d a ranged f rom 4 t o 8 m i l l i o n 1b annua l l y f o r 1954-78, and F l o r i d a ' s ma jo r p roduc t i on area i s f rom t h e I n d i a n R i ve r nor thward (S tee le 1979).

B lue crabs a r e e x p l o i t e d through- o u t t h e year , b u t most a r e taken d u r i n g t he summer and e a r l y f a l l (Music 1979). Hard crabs (crabs w i t h hardened exoske le tons) a re p r i m a r i l y taken i n sha l low wate r by u s i n g t r a w l s , c rab pots , o r t r o t l i n e s i n t h e warmer months. Dredges and scrapes a re used i n deeper o f f s h o r e wate rs i n t h e w i n t e r (Adkins 1972). Use o f c rab t r a w l s on t he A t l a n t i c coas t i s l i m i t e d t o t h e South A t l a n t i c S ta tes , p a r t i c u l a r l y Nor th Caro l ina , where t r a w l s a r e used d u r i n g t he w i n t e r when c rabs a r e r e l a - t i v e l y i n a c t i v e (Sho la r 1979). From 1950 through 1975, t h e number o f c rab f ishermen i n t h e South A t l a n t i c remain- ed r e l a t i v e l y s t ab le , b u t t h e r e was a t r e n d toward reduced use of t r o t l i n e s and inc reased use o f po t s and t r a w l s t o ha rves t c rabs (Table 2). T h i s t r e n d has l e d t o a steady inc rease i n t he importance o f t h e t r a p f i s h e r y i n over - a l l ha rves t ; s i n c e t h e e a r l y 1970's t r a p s have p rov ided 80% o r more o f t h e South A t l a n t i c hard c rab ca t ch w h i l e t he c o n t r i b u t i o n f rom t r o t 1 i n e s has decreased t o l e s s than 2%.

B lue c rabs a r e commonly caught i n c i d e n t a l l y t o shr imp t r a w l i n g and o t h e r f i s h e r i e s , b u t t h i s byca tch o f t e n i s n o t kep t o r represen ts a smal l percentage o f t h e marketed ha rves t .

Peelers o r p e e l e r c rabs (crabs about t o m o l t ) g e n e r a l l y c o n s t i t u t e a smal l percentage o f South A t l a n t i c land ings , b u t a r e a s i g n i f i c a n t aspec t o f t he f i s h e r y . Peelers a r e u s u a l l y

taken by d i p n e t s near t h e shore i n sha l low wate rs d u r i n g t h e warmer months (Newcombe 1945) , o r by t r a w l i n g o r po ts , and a r e p laced i n cages ( f l o a t s ) and a l l owed t o m o l t p r i o r t o market ing. Recent l y mo l ted " s o f t s h e l l " c rabs a r e h i g h l y sought a f t e r by seafood markets and res tau ran t s . Few f ishermen engage i n t h e s o f t s h e l l bus iness because these crabs must be tended c o n s t a n t l y (Adkins 1972). Sho- l a r (1979) i n d i c a t e d t h a t No r th Caro- l i n a was t he o n l y S ta te t h a t r e p o r t e d a s i g n i f i c a n t p e e l e r and s o f t c rab f i s h e r y ; annual l and ings , however, d e c l i n e d f rom about 100,000 1 b p r i o r t o 1965 t o o n l y about 30,000 1b a f t e r 1970.

Management of t he commercial b l u e c rab f i s h e r y i s u s u a l l y l o c a l because most crabs remain w i t h i n one e s t u a r i n e system through t h e i r 1 i v e s . F l o r i d a uses a pe rm i t and l i c e n s e system t o i d e n t i f y t r aps , m in im ize d i s r u p t i o n o f n a v i g a t i o n , and reduce t h e f t o f t r a p s and ca t ch ( W i l l i s 1979). Carapace w i d t h l i m i t s , n e t mesh s izes , con- s t r a i n t s on gear type, c l osed seasons and areas, p r o h i b i t i o n o f t a k i n g sponge c rabs o r o t h e r females, quotas, and l i c e n s i n g have been used by most S ta tes a t va r i ous t imes i n t h e manage- ment o f b l u e crabs. A l l South A t l an - t i c S ta tes have a 127-mm minimum s i z e (carapace w i d t h ) f o r ha rd crabs, and severa l S ta tes have a 76-mm minimum s i z e f o r s o f t o r p e e l e r crabs (Sho la r 1979). F l o r i d a c u r r e n t l y a l l ows up t o 10% o f a f isherman's ha rd crab ca t ch t o be l e s s than 127 rnm i n s i ze .

The b l u e crab a l s o suppor ts a r e c r e a t i o n a l f i s h e r y and a v a r i e t y o f smal l - s ca le commercial ha rves t and sa les ope ra t i ons (sometimes termed "weekend" ope ra to r s ) . Methods i n c l u d e hand l ines , po t s , and c o l l a p s i b l e t r aps . Recrea t iona l f ishermen gene- r a l l y a r e l i m i t e d t o a maximum o f f i v e p o t s (Sho la r 1979). Landings f rom these a c t i v i t i e s have r a r e l y been q u a n t i f i e d .

More (1969) found t h a t f l u c t u a -

Table 2. Numbers o f gear u n i t s , f ishermen, and boats ope ra t i ng i n t h e b l u e c rab f i s h e r i e s o f t he South A t l a n t i c S ta tes , 1950-75 ( f rom Sholar 1979).

Year Pots T r o t 1 i nes Trawls Fishermen Boats

t i o n s o f b l u e crab popu la t i ons were independent o f t h e l e v e l s o f f i s h i n g e f f o r t t h a t occur red d u r i n g h i s study. Pearson (1948) found t h a t t h e s i z e of t h e spawning stock d i d n o t determine t he s i z e o f t h e p o p u l a t i o n t h a t su rv i ved t o commercial age a t f i s h i n g r a t e s t h a t p r e v a i l e d du r i ng t h e years s tud ied . He no ted t h a t f l u c t u a t i o n s i n abundance were r e l a t e d t o r a t e s o f s u r v i v a l d u r i n g t h e f i r s t yea r o f l i f e . Rees (1963) and More (1969) found no d i r e c t r e l a t i o n s h i p between commercial catches and r e c r u i tment o f harves tab le crabs i n subsequent years. Apparent ly , no r e l i a b l e methods o f p r e d i c t i n g popu la t i on f l u c t u a t i o n s e x i s t . Suggested causes o f popu la t i on f l u c t u a t i o n s i n c l u d e extreme c o l d weather o r reduced s a l i n i t i e s f rom

heavy r a i n s (Pearson 1948), p a r a s i t i s m (Hut ton and Sogandares-Bernal 1959), p e s t i c i d e s (Cottam and H igg ins 1946; M i 11s 1952), and p reda t i on (McHugh 1967).

ECOLOGICAL ROLE

B lue crabs per fo rm a v a r i e t y o f ecosystem f u n c t i o n s and can p l a y a major r o l e i n energy t r a n s f e r w i t h i n es tua r i es . A t va r i ous stages i n i t s l i f e c y c l e , t he b l u e c rab serves as p rey and as a consumer o f p lankton, smal l i nve r teb ra tes , f i s h , and o t h e r crabs. It i s an impor tan t d e t r i t i v o r e and scavenger throughout i t s range. Much o f t he i n f o r m a t i o n summari zed below on t r o p h i c r e l a t i o n s h i p s was.

based on work done i n t h e G u l f o f Mexico and i n Chesapeake Ray, b u t general aspects o f t h e b l u e c r a b ' s eco log i ca l r o l e i n those areas should be rep resen ta t i ve o f t he South A t l a n t i c B igh t .

Zoeae a r e phy top l ank t i vorous (Darnel1 1959), and Tagatz (1968) repo r ted t h a t zoeae a l s o r e a d i l y consumed d i n o f 1 age1 1 a tes and copepod naupl i i . The mega1 ops i s omnivorous and consumes f i s h la rvae , smal l s h e l l f i s h , and aqua t i c p l a n t s (Van Engel 1958; Darnel1 1959; Tagatz 1968). Cannibal ism i s common-among a l l l i f e stages o f b l u e crabs (Hay 1905; Churchi 11 1921; Darnel 1 1959; Tagatz 1968).

Hay (1905) s t a t e d t h a t t he pos t - l a r v a l c rab i s predominate ly a scaven- ge r and a cann iba l . Darnel1 (1959) and Adkins (1972) descr ibed t h e b l u e crab as a genera l scavenger, bot tom carn ivore , d e t r i t i v o r e , and omnivore. Food h a b i t s t ud ies have shown t h a t t h e predominant food i tems consumed vary g r e a t l y among 1 ocal i ti es. Some common food i tems a r e dead and 1 i v e f i s h , crabs, o rgan i c deb r i s , shrimp, mo l lusks ( i n c l u d i n g mussels, clams, oys te rs , and s n a i l s ) , and aqua t i c p l a n t s (Newcombe 1945; Darnel1 1959; W i l 1 iams 1965; Tagatz 1968). T r u i t t (1939) found t h a t r oo t s , shoots, and leaves o f ee lg rass (Zos te ra) , d i t c h grass (Ruppia), sea lettuce (U lva) , and s a l t marsh grass ( ~ p a r t i n a - r e commonly consumed by crabs i n s a l t marshes, t i d a l creeks, and o t h e r s h a l l ow e s t u a r i n e areas. Darnel 1 (1958) concluded t h a t mol lusks became t h e dominant food i t e m o f crabs l a r g e r than 120 mm i n w id th .

B lue crabs a r e preyed on by a v a r i e t y o f animals. Eggs c a r r i e d by females a re a f a v o r i t e food o f many f i s h e s (Adkins 1972). La rva l stages a r e eaten by f i s h , s h e l l f i s h , j e l l y - f i s h , comb j e l l i e s , and va r i ous o t h e r p l ank t i vo res (Van Engel 1958). Juve- n i l e b l u e crabs i n G u l f o f Mexico areas were impor tan t p rey o f many f i s h e s such

as spo t t ed sea t r o u t (Cynoscion nebu- 1 osus) , r e d drum (Pogonias c r o s , and sheepshead (Archosargus p robato- u s ) (Fontenot and R o g i l l i o

J u v e n i l e and a d u l t b l u e crabs a r e consumed by mammals and a v a r i e t y of b i r d s .

The b l u e c rab i s t he hos t o f severa l p a r a s i t e s and diseases, b u t many i n f e c t i o n s a r e t e m p o r a r i l y e l i m i - nated d u r i n g mo l t i ng . A f t e r t h e i r l a s t mo l t , a d u l t b l u e crabs can serve as a l odg ing p lace f o r barnacles, b r y - ozoans, and o t h e r s e s s i l e organisms (Darnel 1 1959; W i l l i ams 1965). The barnac les Bal anus amphi tri t e and Che lon ib i a p a t u l a a t t a c h t o t h e cara- pace, b u t gene ra l l y have l i t t l e e f f e c t on the c rab (Darnel1 1959; W i l l i ams 1965). Causey (1961) found t h a t t he s t a l ked barnac le o c t a l asmus 1 owei may c l o q a c r a b ' s q i l l s and q i l l chambers. he-occurrence-of some types o f barna- c l e s can prevent m o l t i n g (S tee le 1979). I n f e c t i o n s by t he amoeba Para- moeba pe rn i c i osa have been respons ib l e f o r massive c rab m o r t a l i t i e s a lona t he eas te rn seaboard (Mahood e t a1 . 1370).

R l ue crabs have been imp1 i cated as c a r r i e r s o f V i b r i o cho la re s t r a i n s t h a t a r e r e s p o n ~ f o r r e a k s o f human cho le ra i n t h e G u l f S ta tes (Moody 1979). Cholera and o t h e r food- borne i l l n e s s e s can be t r a n s m i t t e d t o humans i f crabs a r e improper ly cooked o r s to red .

ENVIRONMENTAL REQUIREMENTS

Temperature

Water temperature i n f l u e n c e s sur - v i v a l , m o l t i n g frequency, and growth of crabs, b u t op t ima l temperatures vary w i t h o t h e r envi ronmenta l para- meters (Zein-El d i n and Griffi t h 1966; Hughes e t a l . 1972; Winget e t a l . 1976). W i 11 iams (1965) found t h a t l a r v a l crabs d i d n o t develop beyond the f i r s t zoeal stage when reared a t temperatures l e s s than 21°C and d i d n o t progress pas t t h e t h i r d zoeal.

stage when r e a r e d a t 30°C o r h i ghe r . Development progressed normal l y a t 25°C when s a l i n i t y was between 20.1 p p t and 31.1 pp t . Cost low (1967) found t h a t s u r v i v a l o f megalops l a r v a e exceeded 70% a t 20°, 25", and 30°C when s a l i n i t y was above 10 pp t , b u t never exceeded 50% a t 15°C. B l ue c rabs avoided m o r t a l i t y d u r i n g an e x t e n s i v e f i s h and shr imp k i l l on t h e Georg ia coas t d u r i n g January 1977 when wa te r temperatures d ipped t o 3°C (Music 1979). T h e i r a b i l i t y t o burrow i n t h e s u b s t r a t e appa ren t l y enab les them t o be i n s u l a t e d f rom c o l d wa te r s f o r s h o r t p e r i o d s (Music 1979; We ins te in 1979). H o l l a n d e t a l . (1971) r e p o r t e d t h a t t h e upper i n c i p - i e n t l e t h a l temperature f o r j u v e n i l e b l u e c rabs was 33°C.

L e f f l e r (1972) measured growth o f c rabs a t f o u r temperatures, s t a r t i n g w i t h 22-mm crabs , and found t h e f o l l o w - i n g mean carapace w i d t h s a f t e r 70 days:

C h u r c h i l l (1921) and Winget e t a l . (1976) a l s o r e p o r t e d t h a t growth r a t e was p r o p o r t i o n a l t o wa te r temperature. L e f f l e r (1972) no ted t h a t growth and m o l t i n g ceased below 13"C, whereas C h u r c h i l l (1921) found t h a t t hey ceased below 15.5"C.

L e f f l e r (1972) found t h a t m o r t a l - i t y was d i r e c t l y p r o p o r t i o n a l t o temperature w i t h i n a 15" t o 34°C range o f exper imenta l c o n d i t i o n s . H o l l a n d e t a l . ' s (1971) exper iments i n d i c a t e d t h a t mo r t a l i t y inc reased a t temperatures above 30°C. L e f f l e r (1972) no ted t h a t c rabs acc l ima ted t o 34°C were hyper- a c t i v e . A c t i v i t y and aggress ion of crabs decreased w i t h tempera tu re u n t i 1 a t 13°C a lmost no movement occur red .

S a l i n i t v

B lue c rabs occupy wate rs r ang ing . f rom 34 p p t t o f r eshwa te r r i v e r s as f a r

11

as 195 km upstream f r om t h e coas t (Tagatz 1968) . Newcombe (1945) s t a t e d t h a t s a l i n i t i e s of 22 t o 28 p p t a r e needed f o r normal h a t c h i n g o f eggs and f o r normal development o f zoeae, b u t s u r v i v a l and growth o f megalops and sma l l j u v e n i l e c rabs may be normal a t s a l i n i t i e s as low as 5 p p t . When s a l i n i t y i s ve ry low, l a r v a e may ha t ch p rema tu re l y and d i e i n t h e p rezoea l s tage (Van Engel 1958). Ho l l and e t a l . (1971) found t h a t s a l i n i t i e s w i t h i n t h e range o f 2-21 p p t had 1 i t t l e e f - f e c t on growth and s u r v i v a l of j u v e n i l e s .

Gunter (1938) s t a t e d t h a t p o s t - l a r v a l b l u e c rabs move i n t o f r eshwa te r and p robab l y do so th roughou t t h e spec ies ' range. Palmer (1974) i n d i c a - t e d t h a t b l u e c rabs may t h r i v e i n h i g h l y s a l i n e , l e s s s a l i n e , and even pu re f reshwate r . Odum (1953) found t h a t o l i g o h a l i n e (100-1000 ppm C1) and n e a r l y 01 i g o h a l i n e (25-100 ppm C1) wa te r s a r e invaded t o a cons i de rab le e x t e n t by b l u e crabs. S p e c i f i c s a l i n i t y l e v e l s a r e n o t c r i t i c a l f o r pos t1 a r v a l crabs (Odum 1953; Cost low 1967; Adk ins 1972; Palmer 1974). The occurrence o f mature males g e n e r a l l y decreases w i t h i n c r e a s i n g sa l i n i t y o v e r 10 p p t (Music 1979). Males can move d i s t ances exceeding 100 km up f r eshwa te r c o a s t a l r i v e r s (Hay 1905; Pearson 1948; Odum 1953).

H a b i t a t S t r u c t u r e

The b l u e c rab i n h a b i t s a l l areas o f e s t u a r i e s t o some e x t e n t ( C h u r c h i l l 1921; Newcombe' 1945; Palmer 1974; Music 1979). We ins te in (1979) found t h a t s h a l l ow s a l t marsh h a b i t a t s were impo r t an t n u r s e r i e s f o r j u v e n i l e b l u e crabs. Mature males p r e f e r creeks, r i v e r s , and upper e s t u a r i e s , b u t t h i s may be a response t o s a l i n i t y r a t h e r t han t o p h y s i c a l f e a t u r e s o f t h e h a b i t a t ( C h u r c h i l l 1921; W i l l i a m s 1965; Music 1979). When n o t mat ing , mature females t end t o remain i n t h e h i g h e r s a l i n i t y areas o t l o w e r e s t u a r - i e s and sur round ing wate rs ( C h u r c h i l l 1921; Van Engel 1958; Palmer 1974; Music 1979).

Adkins (1972) found t h e optimum h a b i t a t f o r sma l l c rabs t o be sha l l ow e s t u a r i n e wate rs w i t h s o f t d e t r i t u s , mud, o r mud-shel l bottoms. La rge r c rabs p r e f e r r e d deeper e s t u a r i n e wate rs hav ing ha rde r bo t tom subs t r a t es .

Other Environmental Fac to r s

Pes t i c i des , h e r b i c i d e s , domest ic and i n d u s t r i a l wastes, a1 t e r a t i o n o f c u r r e n t s , and d e s t r u c t i o n o f marsh- lands a r e among t h e many s t r e s s e s t h a t a f f e c t b l u e c rabs w h i l e t hey occupy nu r se r y areas (Adk i ns 1972). Mahood e t a l . (1970) found t h a t a l l 500 South A t l a n t i c b l u e c rabs examined con ta i ned c h l o r i n a t e d hydrocarbon p e s t i c i d e s . T o x i c i t y inc reased w i t h temperature, b u t decreased w i t h s a l i n i t y ; and t hey found t h a t 1.0 ppm DDT and 10.0 ppm toxaphene were 100% l e t h a l t o a d u l t b l u e c rabs a f t e r 24 and 72 h r s , r e -

s p e c t i v e l y . Pearson (1979) de te rmi ned t h a t b l u e crabs c o u l d d e t e c t nap tha lene (a t o x i c c o n s t i t u e n t o f pe t ro leum) a t l e v e l s encountered a f t e r o i 1 s p i 11 s , b u t d i d n o t s p e c i f y p h y s i o l o g i c a l e f fec ts . Bookhout and. Cost low (1976) found t h a t 0.01- t o 10.0-ppb concentra- t i o n s of M i r ex had no acu te e f f e c t s on m o r t a l i t y o f b l u e c rab l a r v a e f o r 5 days a f t e r ha tch ing ; they a l s o r e p o r t e d t h a t 1.3 t o 1.9 ppb o f Methoxychlor were l e t h a l t o t h e b l u e c rab .

L a u g h l i n e t a l . (1978) i n d i c a t e d t h a t f o r e s t c l e a r c u t t i n g can i nc rease s torm-water runo f f , reduc ing e s t u a r i n e pH and s a l i n i t y f o r s h o r t pe r i ods . I n t h e i r s tudy , mature c rabs were cons i s - t e n t l y more abundant i n c o n t r o l areas t han i n areas where a c i d i c r u n o f f had reduced t h e pH t o l e v e l s below 6.0. S i m i l a r r e s u l t s were observed f o r a c i d i c p u l p m i l 1 e f f l u e n t s ( L i v i n g s t o n e t a l . 1976).

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REPORT DOCUMENTATION ". REmRT 1 3. Rectp~ent 's Accession NO.

PAGE 1. -~W~/0BS-82/11. 19* . I I

4. T i t le and Subtitle

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 of Coastal Fishes and I n v e r t e b r a t e s (South A t l a n t i c ) -- B lue Crab

Michael J. Van Den Avy le and Dean L . Fowler 9. Performing Organization N a m e a n d Address

Georgia Cooperat ive F ishery Research U n i t School o f Fo res t Resources U n i v e r s i t y o f Georgia Athens, Gk 30602

5. R e w r i Da!e

March 1984 ,

,

10. Prolect/Task/Work Unit No. L 7. kuthor(s)

/ 11. Contract(C) or Grant(C) No.

8. Performing Organization Rept. No.

12. Sponsoring Organlzatian N a m e and Address

Nat iona l Coastal Ecosystenis Team U .S. Army Corps o f Engi neers F i sh and W i l d l i f e Serv ice Waterways Experiment S t a t i o n U.S. Department o f the I n t e r i o r P. 0. Box 631 Washington, DC 20240 Vicksburg, MS 39180 15. Supplementar). Notes I*u.s. Army Corps o f Engineers Report No. TR EL-82-4

/ 13. Type of R c p o q 6 Period Covered

16. Abstract (Limot: 2 0 0 words)

Species p r o f i l e s are summaries o f t he 1 i t e r a t u r e on taxonomy, l i f e h i s t o r y and env i ronmenta' requirements o f coas ta l f i s h e s and aqua t i c i n v e r t e b r a t e s . i h e y a r e prep&ed t o a s s i s t w i t h impact assessment. The b l u e crab, C a l l i n e c t e s sapidus, occurs i n l ower reaches o f f resh - wa te r r i v e r s , es tua r ies , and coas ta l waters a long the A t l a n t i c seaboard and G u l f o f Mexico, and the species supports t h e l a r g e s t crab f i s h e r y i n the Un i ted S ta tes . The b l u e c r a b ' s h igh abundance i n es tua r ies , d i ve rse feeding h a b i t s , and importance as p rey f o r o t h e r mar in l animals i n d i c a t e i t s impor tan t r o l e i n t h e s t r u c t u r e and f u n c t i o n o f e s t u a r i n e communities. Female b l u e crabs spawn i n h igh -sa l i n i t y l ower e s t u a r i e s o r coas ta l areas where t h e r e s u l t - i n g l a r v a e are p l a n k t o n i c and develop i n t o j u v e n i l e s a t 5 t o 10 weeks o f age. Juven i les g r a d u a l l y mi g r a t e i n t o sha l lower , l e s s - s a l i ne upper e s t u a r i e s and r i v e r s where they grow and mature a t 1-2 y r o f age. Ma t ing occurs i n the upper e s t u a r i e s a f t e r which females m ig ra te t o areas hav ing h i g h e r s a l i n i t i e s . Growth and s u r v i v a l o f b l u e crabs a re s t r o n g l y a f fec ted by wa te r temperature and s a l i n i t y , b u t to lerances vary w i t h l i f e stage. Larvae r e q u i r e temperatures o f 20°-30°C and s a l i n i t i e s o f 10-30 p p t f o r p rope r development, b u t s a l i n i t y and temperature to lerances a r e broad f o r advanced j u v e n i l e s and a d u l t s . B lue crab< use n e a r l y a l l areas w i t h i n e s t u a r i e s as nu rse ry h a b i t a t , and crab popu la t i ons a re sensi t i vc t o changes i n phys i ca l f ea tu res o r contaminat ion o f these areas.

17. Document A n a l p i s a . Descrvprors

Es tua r ies Feeding S h e l l f i s h Spawning Crustacea Growth

Blue crab Temperature r e q u i rements C a l l i nectes sapi dus H a b i t a t requirements Sal i n i t y r e q u i rements

c. COSATl Fteld/Crouo

la. A v a # l a h l ~ t r Sta tement I 19. Securtly Class (Tho% Reponi I 21. No of Pages

/ U n c l a s s i f i e d 1 16 -- Unl i m i t e d 1 20. Securtry C l a s s F h l 5 P a q c ) i 22. Prlce

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