DETACHMENT OF COMMERCIAL SCALLOP PECTEN-FUMATUS, SPAT FROM SETTLEMENTSUBSTRATES

The ability of chemical irritants and several forms of physiological s tress to induce Pecten fumatus spat to detach from settlement substrat es was evaluated. Hypersaline baths (45 parts per thousand) and exposu re to air (emersion) for 2 h were both found to be effective in induci ng more than 95% of spat to detach from mesh settlement screens. Hyper saline baths, created by the addition of an artificial sea salt to sea water, produced greater spat detachment after 2 h than those created b y equivalent additions of sodium chloride. The rate of detachment in h ypersaline baths was unaffected by increasing temperature from 20-degr ees-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 a s effective as hypersaline baths or air exposure. With the exception o f 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.