Fluid and Sediment Dynamic Effects on Marine Benthic Community Structure

Abstract

Fluid and sediment dynamics affect benthic community dynamics and structure in manifold ways. We single out three community-structuring processes that are both strongly affected and amenable to controlled manipulation: microbial population growth, faunal recruitment, and particle feeding. Attachment and colony growth rates of microbes depend on the details of near-bed fluid exchange. Their emigration and colony growth rates are affected by erosion of microbial filmsand by abrasion during sediment transport. Recruitment and successional patterns of metazoans, especially those resulting from the settlement of weakly swimming, small larvae and juveniles, also are very sensitive to local variations in boundary layer flow pattern and strength. While the importance of particle fluxes to suspension feeders has long been apparent, the foraging patterns of a growing number of surface deposit feeders are being found to reflect a dependence upon sediment transport. Although these three processes have spatial and temporal scales amenable to both laboratory and field experimentation, proper dynamic scaling of laboratory model flows may not always be easy. Even the simplest two-phase (particles plus liquids, where particles can be bacteria, floes, larvae, or sediments) flows must match appropriate laboratory and field Reynolds number, Froude number, particle-fluid density (weight per unit volume) ratio, and the ratio of boundary layer thickness to particle size, if the laboratory flow model is to provide accurate results.