After mating, the female moves back to waters of 

 higher salinity where, within 9 months, it spawns. The 

 eggs are carried on the ventral appendages, giving the 

 crab the appearance of having a sponge attached to the 

 ventral side. This condition is referred to as the "berry 

 state," or the crab is said to be "in berry" (Gaidry and 

 Dannie 1971). Adkins (1972) reported that eggs 

 normally hatch in shallow oceanic water exceeding 

 20%o salinity, but that some females spawn in bays 

 during periods of high salinity. 



The effect of certain physical parameters on blue 

 crabs varies with age and sex. Although crabs are found 

 from fresh to saline waters, adult males are seldom 

 found in salinities above 25%o. Adult females predomi- 

 nate in waters above that level. In Vermilion Bay 

 (Vermilion Basin), males were dominant in catches 

 from the upper reaches of the bay and females were 

 dominant in catches from the lower reaches (Adkins 

 1972). In his study, the highest salinity Adkins meas- 

 ured was 32%o and the lowest was 3.8%(?. 



Rounsefell (1964) reported that abundance of 

 juvenUe crabs appeared to be independent of individual 

 environmental factors such as salinity and temperature. 

 Henry (1967), however, reported that individual 

 growth is accelerated in higher salinities, but tempera- 

 ture and salinity changes have the greatest effect on 

 juveniles. Adkins (1972) found that juveniles are less 

 tolerant to low salinities at high water temperatures 

 and that growth is most affected by temperature. The 

 optimum temperature range for juveniles was reported 

 as 20° to 30° C (68° to 86° F) and the upper lethal 

 temperature is 33° C or 91° F (Holland et al. 1971). 

 The maximum water temperature measured in Vermi- 

 hon Bay by Adkins (1972) was 31° C (88° F) and the 

 minimum was 5° C (41° F). Optimal temperature 

 ranges for adult blue crabs are not available. 



Microbial infections ("burned spot" disease) also 

 occur in the blue crab. The name describes the ap- 

 pearance of shell lesions. The suspected agents of this 

 disease are bacteria and fungi that invade shell abra- 

 sions. Although this disease does not affect edibility, it 

 may be fatal for the crabs. The infection can destroy 

 the chitinous layer on the gill filaments and expose 

 internal tissues to pathogenic organisms. The diseases 

 may be cured by a single molt so that juveniles do not 

 normally contract more than low-level infections. Old- 

 er, more slowly molting crabs are affected most. The 

 disease is most common from October to January and 

 is more prevalent in males than in females; "berried" 

 females are more susceptible than other females. 



The "berry" period is also a crucial time for 

 young crabs because some predators (e.g., the trigger 

 fish) devour egg masses attached to females. Few of 

 the eggs produced will survive to adulthood (Van 

 Engel 1958). 



Pesticides and herbicides, domestic and industri- 

 al waste products, alteration of currents, and destruc- 

 tion of marshlands also limit the abundance of crabs. 



Biological factors are possibly more significant as 

 limiting factors than are physical parameters. Not only 

 are blue crabs food for many predators, they are also 

 affected by microbial and parasitic infections. The 

 "naked" barnacle {Loxothylacus texanus) is the most 

 common parasite of blue crabs. The parasite burrows 

 through soft parts of the juvenile crab at joints, sup- 

 pressing growth and causing atrophy of the gonads. In- 

 fected crabs do not reach commercial size and cannot 

 reproduce (Barnes 1968). After a developmental per- 

 iod, the barnacles emerge and attach to the outer ab- 

 dominal surfaces of the crab. Usually, crabs measur- 

 ing 33 to 78 mm (1.3 to 3.0 in) in width (widest car- 

 pace diameter) are often infected with external naked 

 barnacles. Infections are most common from July 

 through October (Adkins 1972). The external infec- 

 tion is most often found in crabs in high-salinity areas 

 (Ragan and Matherne 1974). The parasite also infects 

 crabs in freshwater, but low salinities appear to inhib- 

 it emergence (Ragan and Matherne 1974). 



Black cysts, caused by fluke larvae, have occur- 

 red in blue crabs in Louisiana and Texas (Moore 

 1969). These cysts do not affect the edibility of crab 

 meat, but they do adversely influence its appearance. 



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