EXPERIMENTAL VARIATION OF NEAR-BOTTOM CURRENT SPEEDS AND ITS EFFECTS ON DEPTH DISTRIBUTION OF SAND-LIVING MEIOFAUNA

Meiofauna are eroded from sediments and transported in the water column. To examine how meiofauna respond to erosive currents, in situ current speeds were altered on an intertidal sandflat located in Bogue Sound, North Carolina, USA in July 1982. Replicates of two different weir designs were erected. One design increased measured current speed and the other, a control, did not. The depth distributions of meiofauna in each treatment and from undisturbed sediment were compared. There were few differences among treatments in depth distribution of the most abundant taxa: nematodes, turbellarians, and ciliates (> 37-.mu.m-long). However, a significant amount of sediment erosion (a mean of almost 0.5 cm in 2 h) occurred in the increased flow treatment. Meiofauna responded to the loss of sediment with no discernable differences in depth distribution relative to the controls. There was some evidence that nematodes were less abundant and ciliates more abundant in the top 0.5 cm of the increased flow treatment. This may indicate that nematodes reond to fast surface current speeds by moving deeper into the sediments, while ciliates manage to remain near the surface even as sediment erodes. The entrainment of meiofauna may be passive but meiofauna clearly exert considerable behavioral influence over their susceptibility to entrainment.