EXPOSURE OF THE SANDY-BEACH BIVALVE DONAX-SERRA RODING TO A HEATED AND CHLORINATED EFFLUENT .3. EFFECTS OF TEMPERATURE AND CHLORINE ON HEART-RATE

The singular and synergistic effects of temperature and free available chlorine in the range of 0.1 to 1.2 ppm on the heart rate of the sand y-beach bivalve Donax serra were investigated. The aim was to identify the possible sublethal impact of a heated and chlorinated effluent on a dense bivalve population near the outfall. The heart rate of adults , in the presence or absence of chlorine, was recorded at 15, 20, 25, and 30 degrees C after daily increments of 5 degrees C from 15 degrees C. One individual from each exposure temperature was transferred dail y to fresh sea water at 15 degrees C to monitor recovery. Heart rate r eached a maximum of 44 beats min(-1) at 25 degrees C from a basal rate of 15 beats min(-1) at 15 degrees C. The heart rate of those exposed to 30 degrees C did not return to basal frequency in fresh sea water a t 15 degrees C. On dosing with chlorine, beat frequency immediately dr opped to half the basal rate as the valves closed and ventilation stop ped. Below 0.6 ppm and <25 degrees C, the basal rate returned within 2 4 hours, and full recovery occurred in fresh sea water at 15 degrees C . Results indicated that plume conditions would not be lethal to D. se rra but that sublethal effects relating to burrowing activity and hear t rate can be expected.