BEHAVIORAL AND SIPHONAL TISSUE RESPONSES OF SCROBICULARIA-PLANA (BIVALVIA) TO ZINC

The effects of zinc added to sea water, to final concentrations of 0. 1-20 ppm, have been studied on the heart rate, valve movements, mortality of Scrobicularia and on both isolated and in situ inhalant siphon preparations. The acute toxicity threshold for added zinc was determined to be about 10 ppm at 10 degree C. The median lethal times for 10 and 20 ppm zinc were 143. 5 and 116. 1 h respectively. Above zinc concentrations of 1 ppm at 6 h exposure, valve closure and bradycardia occur within 10-15 min. Below 5 ppm the valves subsequently opened and heart rate increased over the 6 h period, but in 10 ppm closure and pronounced bradycardia were maintained throughout. Addition of zinc, to final concentrations of 1, 5 and 10 ppm, had no effect on the isolated inhalant siphon. Cutting the cruciform muscles medially resulted in the loss or delay of the response to zinc. Refs.