Storm effects on eelgrass ( Zostera marina L.) and blue mussel ( Mytilus edulis L.) beds

Abstract

The effects of storms on stands of blue mussels Mytilus edulis L. and eelgrass Zostera marina L. at a shallow subtidal site in the Western Baltic were examined. In mixed Zostera/Mytilus stands, the experimental removal of the eelgrass canopy strongly increased the risk of mussel dislodgement during a moderate storm with a median return time of 6.5 months. In contrast, no protection of mussels by eelgrass was found during a series of three intense storms, each of which had a median return time of > 11.5 yr. Also, mussel presence had no effect on the persistence of eelgrass patches (assessed as shoot density) during the moderate storm. The eelgrass meadow had a strong impact on dispersal of mussel clumps under non-storm conditions (wind velocities < 10 m/s). A transplantation experiment with small M. edulis patches showed that drifting mussel aggregates had a tendency to come to rest within eelgrass meadows and may initiate new mussel beds. The results partly explain the preference of blue mussel M. edulis beds for eelgrass Z. marina habitats at shallow subtidal sites of the Western Baltic.