Effects of salinity gradients on the tolerance and bioenergetics of juvenile blue crabs (Callinectes sapidus) from waters of different environmental salinities

Abstract

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‰ S and between 30 and 45‰ 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‰ S for hypersaline individuals. The brackish-water individuals survived 0‰ S. The lowsalinity 21 d LC50 was 0.5‰ 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‰ S. Individuals from the hypersaline population displayed maximal energy absorption at 35‰ S and maximal scope for growth at 35 and 50‰ S.