Hydrodynamic factors affecting behaviour of intertidal meiobenthos

Intertidal meiobenthos may actively emerge from the sediment and enter the water column. Changing hydrostatic pressure and the dimensions of the water column in laboratory experiments did not affect the meiobenthic emergence pattern. Varying current speed in laboratory flumes significantly changed the abundance of Copepoda, Plathelminthes, and Nematoda in the water column while Ostracoda were not affected. Nematode emergence correlates significantly with current speed and is predominantly a result of passive erosion, possibly enhanced by a vertical migration of the specimens to the sediment surface. A current speed > 1 and ≥ 10 cm · s-1 significantly reduced the numbers ofCopepoda and Plathclminthes actively entering the water column. Observation on the swimming behaviour of members of the latter two groups shows that the horizontal component of their active movement is negligible. Presumably, most of these specimens actively enter the water column in order to disperse by currents.