Detection and Avoidance of a Cuprous Oxide Antifouling Paint by Bivalve and Gastropod Larvae (Mollusca)

The reactions of the larvae of seven species of molluscs to a cuprous oxide antifouling paint were investigated in the laboratory. These included larvae of the bivalves Mytilus planulatus Lamarck, Lasaea australis Lamarck, one other unidentified bivalve species; and four other unidentified gastropods. Brief descriptions are given of the unidentified species. By means of currents formed by the foot or tentacle cilia, crawling larvae were able to detect the antifouling paint before they reached it. The behavioural responses included agitated foot or tentacle movements, temporary retraction of larvae into their shells, and turning movements. In six of the species this was followed eventually by more permanent retraction of the larvae into their shells, where they remained stationary for at least 5 min. It is suggested that if similar reactions occurred on a vertical or overhanging surface, such as a ship's hull, the larvae would fall away passively since in the experiments their attaching organs (feet) were automatically withdrawn once the larvae retracted into their shells. This might account for the relative absences of molluscs on ships docked in Sydney Harbour shortly after their antifouling paints have failed, although other groups of fouling organisms have already begun to colonize them.