The effects of simulated estuarine mantle cavity conditions upon the activity of the frontal gill cilia of Mytilus edulis

Abstract

The shell closure mechanism of Mytilus edulis protects the frontal ciliary mechanism against irreversible damage by low environmental salinity levels. Previous experiments had shown that the mantle fluid of mussels exposed to fluctuating salinity regimes was held at a concentration corresponding to about 60% s.w. (20·1‰S) during the period of shell valve closure (Shumway, 1977), while the oxygen tension of the mantle cavity fell rapidly after shell valve closure to 15 mmHg and thereafter remained relatively constant until the valves reopened (Bettison & Davenport, in preparation). These conditions of salinity and oxygen tension were applied to experimental preparations and their ciliary activity assessed. The salinity conditions alone depressed activity by 39·5%. The conditions of oxygen tension alone also produced a depression of 39·5% but there were signs of recovery during the period of simulated shell valve closure. When both salinity and oxygen tension conditions were applied simultaneously a more profound depression of 64·4% was produced by the interacting factors. Exposure of preparations to salinity levels corresponding to the external environment (‘no closure’ simulation) irretrievably damaged the frontal ciliary mechanism on the first exposure to low salinity.