Environmental physiology of the mole crab Emerita asiatica, at a power plant discharge area on the east coast of India

Abstract

Cage experiments at the discharge area of Madras Atomic Power Station (MAPS) facilitated studies of thermal tolerance in Emerita asiatica. At the laboratory, oxygen consumption at various temperatures and varying salinities was also investigated. In the field 100% mortality of crabs was recorded at the Condenser Cooling Water Pumps (CCWP) discharge site compared to no mortality at the Processed Sea Water Pumps (PSWP) site. This observation implicated temperature as a stress factor at the CCWP outfall, because other factors, including residual chlorine and water velocity, were the same at the PSWP and CCWP sites. Laboratory experiments on tolerance revealed that 38·5°C was lethal to mole crabs. The time taken for 100% mortality decreased as the temperature increased from 35 to 40°C. Oxygen metabolism showed a progressive increase with temperature from 29 to 36°C, and declined at 37°C. The influence of salinity on oxygen consumption was marginal at salinities of 20 to 35‰ but, when reduced to 15‰, the oxygen consumption declined. The present study thus indicates that temperature could be the lethal factor, determining the distribution of mole crabs near the power station, where water temperature can exceed 40°C.