Blue crab, continued 



and Evink 1977). Adult males appear to remain in 

 lower salinity waters, and rarely move to higher salini- 

 ties. Adults are known to migrate between estuaries 

 along the Florida Gulf coast (Adkins 1 972b, Oesterling 

 1976). Movement of mated females from Lakes 

 Pontchartrain and Borgne into Mississippi waters oc- 

 curs in the fall and early winter months (Perry 1975). 



Reproduction 



Mode : Sexes are separate (gonochoristic), fertilization 

 is internal, and eggs develop oviparously (Williams 

 1965). 



Mating and Spawning : Mating normally occurs in low 

 salinity waters in the upper reaches of the estuary. 

 Females mate while in the soft shell stage during their 

 pubertal or terminal molt. The females are vulnerable 

 to cannibalism and predation during these molts, and 

 as a result, the recognition of amorous males inter- 

 ested in mating is important. Females approaching 

 their pubertal orterminal molts initiate mating behavior 

 upon recognition of a mature male via olfactory and 

 visual stimuli (Teytaud 1971). Males recognize the 

 females via a pheromone that triggers male mating 

 behavior (Gleeson 1980). Males protect their mates 

 during the females molt. The males accomplish this by 

 grasping the females with their first pair of walking legs 

 and "cradle-carry" her in an upright position under- 

 neath the male. The males transmit their spermato- 

 phores by tube-like pleopods into the females seminal 

 receptacle (Cronin 1 974). The sperm are stored in the 

 seminal receptacle to be released later. Soon after 

 mating, females move to the higher salinity waters near 

 the mouths of estuaries or into the Gulf of Mexico in 

 preparation for spawning. 



Spawning may occur any time from 2 to 9 months after 

 mating, but usually occurs during the spring by females 

 that mated in August-September of the previous year 

 (Van Engel 1 958, Williams 1 965). In the northern Gulf 

 of Mexico, larvae have been found throughout the year 

 except January and February, but their occurrence is 

 low from December to April (Stuck and Perry 1981). 

 Two spawning peaks typically occur in the Gulf, one in 

 late spring and the other during late summer or early fall 

 (More 1 969, Jaworski 1 972, Stuck and Perry 1 981 ). In 

 Florida's St. Johns River, spawning occurs from Feb- 

 ruary through October, with peak occurrence from 

 March through October (Tagatz 1968a). The primary 

 spawning grounds along the Gulf coast of Florida are 

 located off Apalachicola Bay (Oesterling 1976). Eggs 

 are fertilized as they are passed from the ovaries to the 

 seminal receptacle and are extruded out to the pleo- 

 pods (Millikin and Williams 1984). Egg extrusion may 

 be completed within 2 hours (Van Engel 1958). Fe- 

 males may ovulate more than once and sperm can 

 survive forat least one year in their seminal receptacle. 



Fecundity : Fecundity estimates range from 723,500 to 

 2,1 73,300 eggs per spawning (Truitt 1 939), but gener- 

 ally between 1 ,750,000 and 2,000,000 eggs are pro- 

 duced per spawning (Millikin and Williams 1984). The 

 egg mass (sponge) ranges from 24 to 98 g, with an 

 average of 37 g (Tagatz 1965). Females may ovulate 

 and spawn more than once (Millikin and Williams 

 1 984). Second spawnings can occur for some females 

 later in the summer after the first one, and it is possible 

 for a third one to occur, possibly as late as the succeed- 

 ing spring or at an age of three years (Williams 1 965). 



Growth and Development 



Egg Size and Embryonic Development : Approximate 

 ages (after fertilization and extrusion) of blue crab egg 

 masses (sponges) can be estimated according to 

 coloration. Yellow to orange egg masses are from 1 to 

 7 days old. Brown to black egg masses are from 8 to 

 15 days old (Bland and Amerson 1974). Hatching 

 occurs from 14 to 17 days after egg extrusion at 26°C, 

 and 12 to 15 days at 29°C (Churchill 1921). Freshly 

 extruded eggs in the early stages of development are 

 273 x 263 urn, and enlarge to 320 x 278 urn before 

 hatching (Davis 1 965). Hatching occurs in high salinity 

 waters in the lower estuary, and in adjacent Gulf 

 waters. In laboratory experiments, successful hatch- 

 ing did not occur below 20% o (Costlow and Bookout 

 1959). 



Age and Size of Larvae : Newly hatched blue crab 

 larvae are 0.25 mm in carapace width (CW) and usually 

 develop through seven zoeal stages. Laboratory stud- 

 ies indicate that 31 to 43 days are required to complete 

 the zoeal larval stages at 25°C and 26%o salinity 

 (Costlow and Bookout 1959). After the final zoeal 

 stage when approximately 1 mm CW, larvae metamor- 

 phose into the megalopal larval stage (Costlow and 

 Bookout 1959). The optimal salinity and temperature 

 combination for zoeal and megalopal development is 

 30% o and 25°C (Bookout et al. 1 976, Costlow 1 967). At 

 30%o and 25°C, 6 to 12 days were required to develop 

 through the megalopal larval stage into the first crab 

 Guvenile) stage at 2.2-3.0 mm CW (Costlow 1 967). In 

 Mississippi Sound, settlement of blue crab megalopae 

 is episodic, occurring primarily from late summer to 

 early fall (Perry et al. 1 995). Settlement in Mississippi 

 Sound was associated with spring tides and onshore 

 winds, rather than with salinity, temperature, or lunar 

 period (Perry et al. 1 995). Megalopal settlement in the 

 northern Gulf of Mexico may be asynchronous among 

 sites (Rabalais et al. 1995). 



Juvenile Size Range : Juvenile blue crabs may reach 

 maturity within one year along the Gulf coast (Perry 

 1975), while populations in more temperate climates 

 may take up to 20 months (Millikin and Williams 1 984). 

 Salinities from 6 to 30%o do not differentially affect 



101 



