Effects of Antifouling Paints on Settling Larvae of the Bryozoan Bugula neritina L

Abstract

The external anatomy, attachment, and metamorphosis of larvae of the bryozoan Bugula neritina L. are outlined briefly. Larvae placed in dishes of still water containing upward-facing, horizontal, copper antifouling and control paint surfaces aggregated on the former, but failed to attach and metamorphose properly. It is considered that this aggregation effect was initiated by copper ions progressively restricting the swimming movements of larvae passing over the antifouling paint surfaces, which would in time result in an accumulation of larvae in these particular sectors. Larvae no longer capable of swimming actively would gradually descend onto the antifouling paint, and would therefore be exposed to an increased concentration of copper ions. The attachment of larvae to vertical copper, mercury, and control paint strips in slowly moving seawater was compared. The numbers attaching to the control strips was 7 times greater than on the copper, and 20 times greater than on the mercury. The larvae attaching to the antifouling paints were moribund and easily dislodged. Observations made on larvae attempting to attach to vertical copper antifouling strips painted on the side of a shallow tray of still water showed no evidence of a repellent effect. Larvae remained at the antifouling surface until they eventually succumbed and descended to the tray floor in a moribund condition. The attachment of larvae to vertical surfaces of control and antifouling paints was compared in troughs of still water. About 90% of the larvae fell to the trough floor in a moribund condition after coming in contact with an antifouling paint; attachment to the latter was negligible. The effect was similar in all 24 antifouling paints tested. It is suggested that the terms "pre-attachment mortality" and "postattachment mortality" could be used to describe the effects observed in bryozoan and barnacle larvae respectively.