PHYSICOCHEMICAL AND BIOLOGICAL STRESSORS 123 



before salinities were determined. Supplemental eastern Pacific 

 collections were made by a shrimp trawler in Mexico and by hand 

 netting and trapping in Colombia, Mexico, and Panama. 



Jamaica was the main Caribbean study area. I sampled lower 

 reaches of rapidly flowing through nearly stagnant lotic waters, a 

 coastal salt pond, periodically exposed mangrove mud flats, sea grass 

 and algal beds, and featureless bottoms in both estuarine and 

 nonestuarine bays and lagoons, and among coral reefs, by wading, 

 snorkeling, and scuba diving. I used a gill net and traps at one site but 

 trapped and/or hand netted at all others. By standardizing the 

 trapping procedure (using the same trap designs, trapline pattern, 

 bait, and period throughout), I was able to compare crab densities (in 

 number per trap-hr) among sites. Temperatures and water samples 

 were taken from bottom waters in the middle of each site. Most 

 salinities were measured with a refracto meter, but a few were 

 measured by titration. I made supplemental collections in Jamaica, in 

 the Miami area and the middle Florida keys, on the Colombian coast 

 between the Cienaga Grande de Santa Marta and Bahia Concha, and 

 in Curacao. 



At all sites the physical conditions and presence of other species 

 were noted, and, in quantitative Jamaican and Pacific Colombian 

 sites, crabs were sexed, and their carapace lengths were measured 

 immediately after capture. 



Physiological Tolerances 



The hyposalinity tolerances of the common portunids of 

 Jamaica and the Florida keys were tested by acclimating them for at 

 least 30 hr in running seawater (X = 34.5%o in Jamaica and 36.25%o 

 in the keys), then placing them into 10, 25, 37.5, or 50% seawater, 

 and noting survival after 24 hr. 



High-temperature tolerances of Jamaican Callinectes were tested 

 by acclimating them for at least 21 days in the Discovery Bay Marine 

 Laboratory's running seawater system (X = 28.9° C), placing them in 

 39.0° C aerated seawater for 60 min, replacing them in acclimation- 

 temperature running seawater for 24 hr, and examining for survival. 



Desiccation tolerances were tested by acclimating Jamaican 

 Callinectes for at least 30 hr in running seawater, weighing one of 

 each species and replacing it in seawater to recover water lost during 

 weighing, then placing each crab in an individual compartment in a 

 wire-mesh cage in a breezy but shaded corridor between buildings, 

 and noting time until death and lethal weight losses for each species. 



