Stone crab, continued 



to Apalachicola Bay, Florida, and is especially abun- 

 dant in the southwest Florida region (NOAA 1985) 

 (Table 5.1 2). The gulf stone crab occurs from Suwannee 

 River, Florida westward to Laguna Madre and Baffin 

 Bay, Texas, and is relatively abundant in the south 

 Texas estuaries (Table 5.13). The two species are 

 sympatric in Suwannee River, Apalachee Bay, and 

 Apalachicola Bay, and are known to hybridize in this 

 region. 



Life Mode 



Eggs are maintained by the female beneath her abdo- 

 men until hatching. Zoeal larvae are planktonic. The 

 megalopal stage is a transition from the planktonic 

 larval life mode to the epibenthic life mode of juveniles 

 (Stuck and Perry 1 992). As megalopae transform into 

 juveniles, they settle out and are found in areas provid- 

 ing cover such as rubble and seagrass beds. Adults 

 and juveniles are demersal, with adults often forming 

 deep burrows in mud sediments. Juveniles usually do 

 not form burrows, but use readily available crevices or 

 existing cavities in close proximity to food (Lindberg 

 and Marshall 1984). Adult males may exhibit agonistic 

 behavior and compete for burrows, but it is not known 

 whetherthey establish and defend territories or whether 

 their distribution changes between mating and non- 

 mating seasons (Wilber 1 986). Stone crabs have been 

 suggested to be nocturnal; however, equal activity at 

 mid-day and mid-night has been observed, suggesting 

 a crepuscular activity cycle (Powell and Gunter 1968, 

 Lindberg and Marshall 1984). 



Habitat 



Type : All life stages are marine to estuarine. Adult 

 Florida stone crabs are generally found in deeper 

 waters of estuaries or in nearshore waters of the Gulf 

 of Mexico. Adults burrow under rock ledges, coral 

 heads, dead shell, or grass clumps (Costello et al. 

 1979, Bert and Stevely 1989). In seagrass flats and 

 along tidal channels they inhabit burrows and are 

 rarely found on shallow flats during spring and early 

 summer. Juveniles are found in estuaries around 

 pilings, among shells and rocks, and in grass beds 

 (NOAA 1 985). They can change coloration patterns to 

 blend with the background (Bert et al. 1978, Lindberg 

 and Marshall 1984, Williams 1984). Maturing crabs 

 movetodeeperestuarineand nearshore waters. Adults 

 have been collected at depths ranging from 5 to 54 m, 

 but are not generally abundant in offshore waters 

 (Bullis and Thompson 1965, Bert and Stevely 1989, 

 Stuck 1 989). The Florida stone crab occurs at greatest 

 densities in seagrass, rocky outcrops, and hard bot- 

 tom. It rarely occupies oyster bars, while the gulf stone 

 crab commonly inhabits oyster bars, sandy or muddy 

 bottoms, as well as seagrass or rocky habitats (Bert 

 and Harrison 1 988). Gulf stone crabs occur both sub- 

 and intertidally, whereas the Florida stone crab is 



primarily subtidal (Wilber 1989a, Wilber 1992). In 

 addition, males are more likely to be found in intertidal 

 areas in the summer, and females in subtidal habitats 

 (Wilber 1989a). Highest catches of gulf stone crab in 

 Mississippi Sound are in the immediate vicinity of 

 barrier island passes in depths less than 12 m, and they 

 are not generally abundant in offshore waters (Stuck 

 1989). 



Substrate : Florida stone crabs appear to require sub- 

 strate suitable for refuge, using either available struc- 

 ture or excavated burrows. They are found in rock or 

 shell substrates, seagrass meadows, and pilings 

 (Costello et al. 1979), and are known to excavate 

 burrows in emergent hard substrate or in seagrass 

 ( Thalassia) beds (Bert and Stevely 1 989). In one study 

 in Galveston Bay, gulf stone crabs were found to be 

 more abundant on oyster reefs than in vegetated or 

 non-vegetated habitat (Zimmerman et al. 1989). 



Physical/Chemical Characteristics : 

 Temperature - Larvae: Florida stone crab larvae do not 

 develop beyond the megalopal stage at temperatures 

 below 20° C (Ong and Costlow 1970). Optimal 

 conditions for zoeae appear to be 30°C at 30 to 36%o. 

 Megalopae are sensitive to low salinities and extreme 

 temperatures (Lindberg and Marshall 1984). In a 

 factorial experiment of salinity and temperature, sur- 

 vival of Florida stone crab larvae (zoeae) was found to 

 be highest at 30°C and 30%o, and diminished at salini- 

 ties and temperatures above and below these values 

 (Brown et al. 1 992). The early zoeal stages (zoeae 1 - 

 3) were strongly affected by both temperature and 

 salinity, whereas the later stages (zoeae 4-5) were less 

 affected by salinity. Larval developmental rate and 

 molting frequency were accelerated by increasing tem- 

 perature, but not by salinity. 



Temperature - Juveniles and Adults: Juvenile and 

 adult stone crabs are eurythermal and, in general, can 

 tolerate waters ranging from 8°-32°C. In cooler tem- 

 peratures they become inactive and may seal their 

 burrows with mud (Powell and Gunter 1 968). Muscular 

 movements of juvenile Florida stone crab virtually 

 cease below 15°C (Brown et al. 1992). In Mississippi 

 Sound, juvenile gulf stone crabs have been collected at 

 temperatures from 7°-33°C, but mostly above 25°C 

 (Stuck and Perry 1992). Molting and spawning are 

 affected by temperature (Lindberg and Marshall 1984, 

 Williams 1984), and low temperatures are known to 

 inhibit molting (Brown et al. 1992). Ovigerous gulf 

 stone crab females are not generally found at <18°C, 

 and are most common at >22°C (Stuck and Perry 

 1992). In a factorial experiment of salinity and tem- 

 perature, survival of juvenile Florida stone crab was 

 found to be 100% at 15°, 20°, and 25°C (Brown et al. 

 1992). 



111 



