Effects of copper on development and survival rate of Paphia malabarica Chemnitz larvae under low saline condition.

Venerid clam, Paphia malabarica Chemnitz, is the commercially exploited species distributed exclusively in Vembanad Lake and Ashtamudi estuary, along the south west coast of India. In this study, the survival rate and development of P. malabarica larvae were studied for 3 days in ambient salinity (33), copper (2.5 microg Cu2+ l(-1)), reduced salinities (25 and 20) and a combination of copper in low salinities. No significant differences were found in larval development between treatments. The survival rates decreased considerably with low salinities although the combination of copper and low salinity gave synergistic effects. The reduced survival in low salinities would limit population growth of this species in estuarine areas experiencing low salinities and also explains the absence of larval settlement on habitats close to harbors or river mouths.