Stone crab, continued 



Salinity - Larvae: Ong and Costlow (1 970) reported that 

 Florida stone crab zoeae have low survival rates at low 

 salinities (20-25%o) at 20°C; and complete mortality 

 occurs in a salinity of 10%o. At 23°-25°C, low survival 

 of zoeae has been observed below 27%o (Porter 1 960). 

 It has been suggested that gulf stone crab larvae may 

 be more tolerant of low salinities than Florida stone 

 crab larvae. In Mississippi Sound, gulf stone crab 

 megalopae are commonly found in salinities of 15- 

 25%o, and have been collected from salinities as low as 

 9% (Stuck and Perry 1992). 



Salinity - Juveniles and Adults: Juveniles and adults of 

 both species are considered euryhaline, although they 

 are usually found in higher salinities. It has been 

 suggested that M. mercenaria may be less tolerant of 

 lower salinities and/or prefer higher salinities than M. 

 adina (Williams and Felder 1986). Juvenile Florida 

 stone crabs are generally found in salinities >24%o 

 (Bender 1971). In Mississippi Sound, gulf stone crab 

 juveniles have been collected in salinities from <4 to 

 34%o, although they are most abundant in salinities 

 from 20-29% o (Stuck and Perry 1 992). Gulf stone crab 

 adults are found in salinities above 1 3%o in Mississippi 

 Sound (Stuck 1989, Stuck and Perry 1992), but they 

 have been reported from salinities as low as 1 1 .6%o in 

 Texas (Powell and Gunter 1 968). In a factorial experi- 

 ment of salinity and temperature, survival of juvenile 

 Florida stone crab was found to be 1 00% at 25, 30, 35, 

 and 40% o (Brown et al. 1 992). In a similar experiment 

 comparing survival of juvenile gulf stone crab and 

 Florida stone crab, it was found that gulf stone crab had 

 greater tolerance for low salinity and low temperature 

 than did Florida stone crab (Brown and Bert 1993). 

 This may be due to species-specific differences, or to 

 local adaptation of populations. These differences 

 generally reflect the known biogeographic and in- 

 shore/offshore distribution of the two species (Brown 

 and Bert 1993). 



Dissolved Oxygen (DO): Adults are fairly tolerant of 

 periods of low DO, although long-term effects are not 

 well known (Lindberg and Marshall 1984). 



Turbidity: Stone crabs may become more active in 

 turbid waters, possibly as a result of waves and turbu- 

 lence that agitate the bottom substrate (Savage et al. 

 1975). 



Migrations and Movements : Movements by Florida 

 stone crabs of up to 30 km/year have been recorded in 

 Florida's Everglades National Park (Bert and Harrison 

 1988), but most movements appear to be short-range 

 and along shore (1.6-8.0 km) (Ehrhardt 1990). Minor 

 movements by the females from grass flats to deeper 

 waters to avoid especially high or low temperatures 

 have been noted (Lindberg and Marshall 1984, NOAA 



1985, Wilber 1986). In northwest Florida's "hybrid 

 zone", adult females may migrate into intertidal oyster 

 habitats (Wilber and Herrnkind 1 986). This is followed 

 by the gradual emigration of nearly all crabs from the 

 intertidal region in the late fall and early winter, prob- 

 ably in response to falling temperature. 



Reproduction 



Mode : Stone crabs have separate male and female 

 sexes (gonochoristic), and exhibit sexual dimorphism 

 (Savage 1971, Bert and Stevely 1989). 



Mating and Spawning : Mating occurs from November 

 to March, but primarily in January and February. It is 

 sequenced with the spawning season, generally from 

 March to November. In Florida Bay, peak mating 

 periods have been noted in April and October (Bert and 

 Stevely 1989). Mating takes place within a burrow or 

 crevice (Savage 1971, Bert and Stevely 1989, Wilber 

 1 989b). Males will guard the females after copulation, 

 and for longer periods after females molt if another 

 male stone crab is present. Sperm are transferred from 

 the male to the female within spermatophores which 

 are stored by the female in the seminal receptacle. 

 Only a portion of the sperm is used at a spawning 

 period, some being maintained for later spawns. A 

 female can spawn up to six times before mating again. 

 After hatching one batch of eggs, a female may deposit 

 a new egg mass within a week. Fertilized eggs are 

 released into a basket formed by the female's ex- 

 tended abdomen and the exopods of her abdominal 

 appendages. The eggs are attached to hairs on the 

 exopods by a secretion. Temperature and photoperiod 

 are primary regulators of spawning frequency (Bert et 

 al. 1 978, Lindberg and Marshall 1 984, Williams 1 984, 

 Bert et al. 1986). In south Florida, most spawning of 

 Florida stone crabs is from March to October, with 

 peaks in May and September (Sullivan 1979). How- 

 ever, spawning can also occur throughout the year in 

 warm areas such as Florida Bay. Ovigerous gulf stone 

 crabs occur in Mississippi Sound from March through 

 October, with apparent spawning peaks in June and 

 September (Stuck and Perry 1992). Evidence indi- 

 cates that females molt and mate soon after spawning 

 is terminated. The movement of adult females to 

 oyster reefs in the fall suggests this may be an impor- 

 tant mating habitat for first and second year adults 

 (Wilber 1986). 



Fecundity : A single female can produce between 4 and 

 6 egg masses (sponges) during a spawning season, 

 averaging 4.5 spawnings per molt (Cheung 1 969). Ten 

 spawnings during an intermolt period have been re- 

 ported from a single female held in the laboratory 

 (Yang 1971). Each sponge may contain 0.5 to 1.0 

 million eggs. Wilber (1989a) observed a maximum 

 number of five clutches carried by a single female in a 



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