STORM EFFECTS ON EELGRASS (ZOSTERA-MARINA L) AND BLUE MUSSEL (MYTILUS-EDULIS-L) BEDS

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 B altic were examined. In mixed Zosrera/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 du ring a series of three intense storms, each of which had a median retu rn time of > 11.5 yr. Also, mussel presence had no effect on the persi stence of eelgrass patches (assessed as shoot density) during the mode rate storm. The eelgrass meadow had a strong impact on dispersal of mu ssel clumps under non-storm conditions (wind velocities < 10 m/s). A t ransplantation experiment with small M. edulis patches showed that dri fting 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 ha bitats at shallow subtidal sites of the Western Baltic.