Sediment water coupling in permeable shallow water sediments

This study investigates transport processes into sandy sediments of the continental shelf, which are characterized by an intense water and substance exchange with the overlying water column. It will be shown that the permeability of those sediments is a critical factor for degradation of organic matter in the ocean. The main focus of this study is formed by a series of studies in coral reef ecosystems, which exhibit as shallow water habitats a maximal coupling between water column and sandy sediments. The results of this study indicate that corals, main producers of organic matter in reef ecosystems, importantly to the nutrition of the reef sediments. Especially, mucus exudates are produced in large quantities by the corals. Ensuing drifting mucus aggregates trap a multiplicity of particles from the water column resulting in fast sedimentation rates of this material and subsequent rapid mineralization in the permeable reef sands. These very active carbonate sands, characterized by a high density of fauna and microbes, function as gigantic biocatalytical bioreactors. There is evidence that we found a new way of nutrient recycling in coral reef ecosystems. This could possibly contribute to explain the high productivity of the highly oligotrophic reef environment and, a contradiction commonly called „coral reef paradox“.