EFFECTS OF SALINITY GRADIENTS ON THE TOLERANCE AND BIOENERGETICS OF JUVENILE BLUE CRABS (CALLINECTES-SAPIDUS) FROM WATERS OF DIFFERENT ENVIRONMENTAL SALINITIES

Juvenile Callinectes sapidus Rathbun were collected from brackish and hypersaline coastal environments in August 1986 and July 1987, respectively. The brackish collection site was a salt-marsh near Grand Isle, Louisiana (USA), and the hypersaline site was in the barrier island system on the north end of the Laguna Madre near Corpus Christi, Texas (USA). On the dates of collection, salinities fluctuated daily between 20 and 30 parts per thousand S and between 30 and 45 parts per thousand S at the brackish and hypersaline collection sites, respectively. The high-salinity 21 d LC50 (50% mortality) was 56.0 for brackish-water individuals and 66.5 parts per thousand S for hypersaline individuals. The brackish-water individuals survived 0 parts per thousand S. The low-salinity 21 d LC50 was 0.5 parts per thousand S for the hypersaline individuals. Respiration and excretion comprised a small portion of the energy budget and did not vary with salinity for individuals from brackish water. However, both respiration and excretion increased with decreasing salinity in individuals from the hypersaline environment. Respiration accounted for more energy than excretion. As energetic expenditure (due to respiration and excretion) was relatively small, scope for growth usually paralleled energy absorption. Scope for growth responses to salinity differed significantly between crabs from the two environments. Peaks in scope for growth for both the brackish-water and hypersaline individuals corresponded to salinities normally encountered by these crabs in their natural habitats. Individuals from the brackish-water population had maximal energy absorption and scope for growth at 10 and 25 parts per thousand S. Individuals from the hypersaline population displayed maximal energy absorption at 35 parts per thousand S and maximal scope for growth at 35 and 50 parts per thousand S.