Sediment mediated species interactions in coastal waters

Self-structuring in marine sediment communities is achieved by the mobility of the organisms, the trophic web, and biogenic transformations of the habitat. The latter are: bioconstruction and biotarbations, sediment stabilisation and destabilisation, with facilitating and inhibiting effects. This cursory overview intends to show that in near-shore mud and sand, biogenic habitat transformations pervade all community interactions. Consequently these deserve as much attention in benthic ecosystem analyses as do trophic pathways. Abundant phototrophs and suspension feeders tend to accumulate sediment and organic matter. Underneath phototrophic mats, composite layers of anaerobic microorganisms abound. Benthic animals provide anchorage to tufts of algae, and these in turn provide shelter and food for mobile benthos. Rooted plants slow down hydrodynamics and generate complex habitats above the sediment surface but below a meshwork of roots may inhibit burrowing animals. Abundant suspension feeders stabilise sediments, and may build loose hummocks, multi-species epibenthic thickets or solid reefs, accommodating diverse epibenthic assemblages. Their raised and rough surfaces enhance turbulence. Below the sediment surface, tubes and burrows of sessile or discretely motile animals provide microoxic habitats for diverse assemblages of small organisms. At the surface, mucus of motile organisms increases sediment cohesion. Accumulated dead hardparts of the benthos support epibionts when at the surface but cause resistance to the burrowers below. Reworking and irrigation of the sediment by the infauna increases oxygenation, and particulate and solute fluxes with the overlying water. Mounds and pits generated by resident burrowers as well as by large visiting grazers and predators further diversify the benthos. All these bioengineered structures and processes generate dynamic and complex habitat-mediated interaction webs, affecting and meshed into the trophic web, which they may rival in overall importance in the self-structuring of the benthos in coastal marine sediments. (C) 2002 Elsevier Science B.V. All rights reserved.