Attachment and orientation ofMytilus EdulisL. in flowing water

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Abstract
The effects of flow velocity and shell orientation in a flow field on byssus thread attachment were investigated in the blue mussel Mytilus edulis L. in a flume flow. The number of established byssus threads and the strength of byssus attachment were significantly affected by flow velocity. No effect on number of attached byssus threads was observed relative to orientation of the mussel, but mussel orientation at termination of the high flow experiments was significantly dominated by the position: ventral upcurrent. By measuring the number of established byssus threads and the strength of attachment of individual detached byssus threads the potential strength of attachment was estimated. In still water the measured strength of attachment constituted 21% of the estimated potential strength of attachment, but in a 19.4 cm sec-1 flow the measured strength of attachment constituted 81%. This observation indicates, that the correlation between the number of etablished byssus threads and the force of attachment is not a simple function. The critical velocity at which a mussel was dislodged by flow was investigated as a function of mussel orientation. This experiment showed that the critical velocity was significantly affected by orientation of the mussel and shell height, where the orientations ventral and umbo upcurrent showed the highest critical velocities. No difference in drag was found between the orientations umbo upcurrent and ventral upcurrent, which were found to be the dominant orientations when mussels were kept in a flume flow, indicating orientations of low drag force.