BENTHIC FAUNAL SUCCESSION IN A COVE ORGANICALLY POLLUTED BY FISH FARMING

In the past two decades, fish farming using net cages has developed in the coastal waters throughout Japan. Such fish farming has allowed the production of large amounts of valuable fish and their supply to the markets in major cities on a regular basis. However, fish farming is often followed by serious organic pollution of the water and bottom sediment in the vicinity of the cages since approximately 90% of the food for the fishes results in organic discharge to the environment around the fish farm. Organic pollution of soft bottom sediment is apt to be accompanied by the development of reducing conditions in the sediment and deoxidization of the bottom water, as a results of the decomposition of abundant organic matter. The benthic communities in such organically polluted areas are subject to catastrophic environmental disturbances. We have assessed the environmental conditions and abundance of benthic communities in a specific cover since 1966. The results of the present study clearly show the dramatic changes in fauna and the reduction in the abundance of members of the benthic communities in the cover that have accompanied the progress of the organic pollution associated with fish farming.