Floating behaviour in the tellinid bivalve Macoma balthica (L.).

The tellinid bivalve Macoma balthica from the Dutch Wadden Sea mudflats achieved secondary distribution by a floating behaviour after stimulation by low ambient temperature in slow-moving sea water (salinity 25‰). Floating behaviour among responding mussels began with burrowing displacements as their foot was directed towards the sediment surface. After extreme protrusion of the foot they became buoyant and were able to float. Floating behaviour was observed to last for periods of 1.5 h. During this active sequence frequent stops (range 2-6) were followed by resting periods on the sediment. In stagnant water at a constant temperature, mussels displayed burrowing displacement in a rhythmic manner with one peak of activity during the dark period of the day. Mussels previously acclimatized at high temperatue showed significantly stronger responses to current and temperature stimuli. Adult mussels as well as juveniles performed the floating behaviour. The paper discusses the ecological significane of secondary distribution.