Upper Temperature Tolerances of Some Estuarine Bivalves

Abstract

Twenty-four hour, upper lethal temperatures were determined at different acclimation levels for Mya arenaria, Macoma balthica, Mulinia lateralis and Gemma gemma. Limited information was obtained for Macoma phenax. Young Mya arenaria and Macoma balthica were more tolerant of high temperature than were older clams of the same species. This difference, and that between the two species, may be related to their vertical benthic distribution. Both species were less tolerant of high temperature than Gemma gemma and the more southerly ranging Macoma phenax. Mulinia lateralis was similar to Mya arenaria and Macoma balthica in its high temperature tolerance, although it ranges further to the south. If the less tolerant Mya were killed by high environmental temperature, the more resistant Gemma could then occupy the vacated habitat, precluding resettlement of Mya due to larval Mya-adult Gemma competititon for space. Excessive thermal discharge over Chesapeake Bay benthos in summer could affect spawning patterns of Mya and Macoma balthica, eliminate Mya and influence Mya-Gemma competitive interactions.