Energy Flow in the Kromme Estuarine Ecosystem, St Francis Bay, South Africa

Abstract

An energy flow network was constructed for the Kromme estuary, South Africa. Extensive data, collected on this estuary, were used to calculate the energetics of each of the 27 compartments identified in this system. The model consists of three non-living and 24 living compartments. The non-living compartments were dissolved organic carbon (DOC), suspended and sediment particulate organic carbon (POC), while the living compartments consisted of four plant groups, three bacterial groups and 17 animal groups. The animals range from meiofauna to macrofauna and fish. Biomass of all compartments were estimated in mg C m −2and exchanges in mg C m −2day −1. It was found that the main primary producers are the marsh halophytes and macrophytes. It seems that although the salt marshes cover only 38% of the Kromme estuary, the marsh halophytes contribute 78% of the total primary production, making it the most important producer in this estuary. Less than 10% of the halophyte production enters the grazing food-chain, with the remainder being broken down to sediment detritus. This indicates that the sediment detritus, as well as the animals that feed on it, forms the most important part of this food-web.