Hydrodynamic processes affecting benthic recruitment1

Abstract

Recruitment of animals into initially dofaunated sites containing simulated stalks of a marsh grass was studied on an intertidal sandflat. Laboratory flume experiments were used to predict the effects of these structures on near‐bed flow, the sediment size‐frequency composition, and the patterns and rates of benthic recruitment. The effects of simulated stalks on both rates of fluid transport near the bed and boundary shear stress change profoundly with their numerical density. Patterns of sedimentation in the field and patterns and rates of recruitment of several taxa depended strongly on the presence and numerical density of these structures, in agreement with a priori predictions assuming passive (i.e. purely hydrodynamic) dispersal. Hydrodynamic (or other physical) effects of manipulation are important and form an additional, but infrequently posed, null hypothesis against which biological effects such as substrate selection, competition, predation, or disturbance should be tested.