DETACHMENT OF COMMERCIAL SCALLOP PECTEN-FUMATUS, SPAT FROM SETTLEMENT SUBSTRATES

The ability of chemical irritants and several forms of physiological stress to induce Pecten fumatus spat to detach from settlement substrates was evaluated. Hypersaline baths (45 parts per thousand) and exposure to air (emersion) for 2 h were both found to be effective in inducing more than 95% of spat to detach from mesh settlement screens. Hypersaline baths, created by the addition of an artificial sea salt to seawater, produced greater spat detachment after 2 h than those created by equivalent additions of sodium chloride. The rate of detachment in hypersaline baths was unaffected by increasing temperature from 20-degrees-C to 26-degrees-C, but was depressed at 11-degrees-C. Addition of magnesium chloride (27 g/kg) to seawater and reduction of seawater pH to 2 were also effective in increasing spat detachment rate, but not as effective as hypersaline baths or air exposure. With the exception of spat exposed to seawater containing 115 mg/kg available chlorine, no significant mortality and > 95% reattachment occurred within 24 h of all detachment methods tested.