Effects of macroalgae and biofilm on settlement of blue mussel (Mytilus edulis L.) larvae

Marine macroalgae are covered by a biofilm community of bacteria and diatoms. In this study, the influences of macroalgae and their biofilm community on the settlement and behaviour of epibionts such as the blue mussel were examined. Under field conditions (White Sea, Kandalakshsky Gulf), larvae of Mytilus edulis settled predominantly on thalli of the filamentous green algae Cladophora rupestris compared to thalli of the brown macroalgae Laminaria saccharina and Fucus vesiculosus. In laboratory experiments biofilm and wash-outs from C. rupestris attracted larvae while those from L. saccharina repelled blue mussel larvae. Biofilm and wash-outs from F. vesiculosus had no behavioral effect on the larvae. In general, biofilm had the same effect on the behaviour of the larvae as the macroalgae themselves. Field experiments which were designed to decrease flow around substrates also demonstrated that thalli of C. rupestris attracted larvae, but those of L. saccharina repelled them. It is concluded that macroalgae and biofilm affect substrate selection by blue mussel larvae, both by excretion of signals (repellents or attractants) and toxic substances.