Swimming behaviour of marine bivalve larvae in a flume boundary- layer flow: evidence for near-bottom confinement

Abstract

The swimming behaviour of settling larvae of Cerastoderma edule was studied in still water and in a flume boundary-layer flow. In still water and slow flow the larvae swam upward in helices with high directionality, interpreted as morphological geotaxis. By reducing velar propulsion larvae regularly descended towards the bottom due to gravity. In moderate and fast flow (5-10 cm s-1) larvae became confined to the viscous sublayer, where they slowly drifted in the streamwise direction at 0.45-1.6 mm s-1, <1 mm above the sediment surface, periodically making contact with the bottom. At flow velocities >15 cm s-1 the steady near-bottom drift changed to bed-load transport of tumbling larvae with high probability of resuspension. -from Authors