Blue crab, continued 



growth of juveniles (Millikin and Williams 1 984). Tagatz 

 (1 968b) observed that growth per molt remained simi- 

 lar regardless of temperature (summer vs. winter) in 

 the St. Johns River, Florida, but that intermolt intervals 

 were three to four times longer in the winter. Juvenile 

 blue crabs may range in size from approximately 2 mm 

 CW when the first crab stage is attained, to over 150 

 mm CW. Maturity in blue crabs is attained over a wide 

 range of carapace widths (Perry pers. comm.). Guillory 

 and Hein (in press) sampled 2,925 blue crabs in 

 Louisiana estuarine waters, and reported that 50% of 

 males were mature by 1 10-1 15 mm CW, and 50% of 

 females were mature by 1 25-1 30 mm CW. The small- 

 est mature male was 96 mm CW, and the smallest 

 mature female 1 1 3 mm CW. One hundred percent of 

 the males were mature by 130 mm CW, and 100% of 

 the females by 160 mm CW. 



Age and Size of Adults : Tagatz (1 968b), sampling blue 

 crabs from St. Johns River, Florida, reported mean 

 carapace widths and ranges: adult males averaged 

 147 mm, ranging from 117 mm to 181 mm; adult 

 females averaged 148 mm, ranging from 128 to 182 

 mm. Tagatz (1965) reported a maximum carapace 

 width of 246 mm (male), and a heaviest weight of 550 

 g (male), from commercial catches in the St. Johns 

 River, Florida. Adult males generally weigh more than 

 females of a given size (excluding gravid females) 

 (Millikin and Williams 1 984). Females may vary in size 

 from mature at 51 mm to immature at 177 mm. Fe- 

 males mate at their terminal molt, males continue to 

 grow and molt after reaching sexual maturity. The blue 

 crab has an estimated life span of 3-4 years (Tagatz 

 1 968a). Growth equations for the blue crab have been 

 calculated by Pullen and Trent (1970). 



Food and Feeding 



Trophic Mode : This crab is an omnivore, scavenger, 

 detritivore, predator, and cannibal that feeds on a wide 

 variety of plants and animals, selecting whatever is 

 locally available at any time (Costlow and Sastry 1 966, 

 Laughlin 1982). Its feeding habits change with its 

 ontogeny. Larval blue crabs are believed to feed on 

 phytoplankton and zooplankton, while juveniles and 

 adults are described as general scavengers, bottom 

 carnivores, detritivores, and omnivores, that consume 

 whatever is in the area (Costlow and Sastry 1966, 

 Laughlin 1982). 



Food Items : Food habits of the blue crab are variable, 

 changing with season of the year, geographic location, 

 and the developmental stages of its life cycle (Laughlin 

 1982, Steele and Perry 1990). Zoea consume phy- 

 toplankton and copepod nauplii. Aquaculture proto- 

 cols recommend that zoeal stages be fed sea urchin 

 embryos, Artemia nauplii, and/or rotifers (Millikin and 

 Williams 1 984, Schmidt 1 993). The megalopal stage is 



omnivorous and consumes fish larvae, small shellfish 

 and aquatic plants. The diet of juveniles and adults 

 consists mainly of molluscs, crustaceans, and fish 

 (Tagatz 1968a, Jaworski 1972, Alexander 1986). 

 Laughlin (1982) evaluated stomach contents of blue 

 crabs from Apalachicola Bay, Florida and observed the 

 following: small juveniles (less than 31 mm carapace 

 width) fed mainly on bivalves, plant matter, ostracods, 

 and detritus; intermediate juveniles (31-60 mm) fed 

 mostly on fishes, gastropods, and xanthid crabs; large 

 juveniles and adults (greater than 60 mm) fed on 

 bivalve molluscs, fishes, xanthid crabs, and smaller 

 blue crabs. Molluscs known to be food items for blue 

 crab include American oyster, hard clams, coot clam 

 (Mulina lateralis), Atlantic ribbed mussel (Geukensia 

 demissa), darkfalsemussel (Mytilopsis leucophaeata), 

 scorched mussel (Brachidontes exustus), Atlantic 

 rangia, and marsh periwinkle (Littorina irrorata) (Millikin 

 and Williams 1984). The blue crab has been charac- 

 terized as an opportunistic benthic omnivore, whose 

 food habits are governed by availability of food items 

 (Darnell 1959, Seed and Hughes 1997). Feeding 

 generally decreases as temperature decreases, espe- 

 cially from 34° to 13°C (Leffler 1972). 



Biological Interactions 



Predation : Blue crab postlarvae can be 1 to 1 00 times 

 more abundant in estuaries of the U.S. Gulf Coast (AL, 

 MS, TX) than along the East Coast (DE, VA, NC, SC), 

 but this does not necessarily result in elevated abun- 

 dance of juveniles and higher fishery landings (Heck 

 and Coen 1995). Abundances of blue crab juveniles 

 are similar in estuaries of the two regions, suggesting 

 that there is higher mortality of recently-metamor- 

 phosed juveniles in the Gulf region, possibly as a result 

 of predation (Heck and Coen 1995). Numerous spe- 

 cies of fish, mammals, and birds prey on the blue crab 

 (Killam et al. 1992). Different species of shrimp, 

 including Palaemonetes pugio, have been found to 

 prey on blue crab megalopae (Olmi 1990). Fish that 

 consume zooplankton, such as herring and menhaden 

 species, are also probably important predators of blue 

 crab larvae (Millikin and Williams 1 984, Schmidt 1 993). 

 Major fish predators on juveniles are snook, black 

 drum, juvenile and adult red drum, Atlantic croaker, 

 spotted seatrout, and sheepshead (Fontenot and 

 Rogillio 1 970, Boothby and Avault 1 971 , Adkins 1 972b, 

 Fore and Schmidt 1973, Bass and Avault 1975, 

 Overstreet and Heard 1978a, Overstreet and Heard 

 1978b). They have also been found in the stomach 

 contents of the sandbar shark (Carcharhinus plumbeus) 

 and spot (Levine 1980, Medved and Marshall 1981, 

 Rozas and Hackney 1984). In addition, adult blue 

 crabs will often cannibalize juveniles (Costlow and 

 Sastry 1 966, Martinez pers. comm.). Several freshwa- 

 ter fishes may prey on blue crab in oligohaline waters, 

 including alligator gar (Lepisosteus spatula), spotted 



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