EFFICIENCY OF THE DECOMPOSITION OF ORGANIC-MATTER, LOADED ON THE SEDIMENT, AS A RESULT OF THE BIOLOGICAL-ACTIVITY OF CAPITELLA SP I

Over the past three decades, fish farming in net pens has been extensi vely developed in Japanese coastal seas. Recently, however, many fish farms have suffered from organic pollution of the bottom environment, due to the vast discharge of organic matter from the fish farms themse lves. During the summer, the bottom water in organically polluted area s is apt to be anoxic. High levels of hydrogen sulphide are often prod uced in the organically polluted sediment. We have attempted to treat the organically polluted sediment by exploiting the biological activit ies of a deposit-feeding polychaete, Capitella sp. I. In experiments i n the laboratory, the size of colonies of this species increased very rapidly, and the organic matter that was loaded on the sediment was ve ry efficiently decomposed. The proliferating colonies also promoted th e oxidation of the reduced sulphides in the sediment. The results of t his study indicate that dense patches of more than 59 000 individuals m-2 have the potential to exhaust the organic matter loaded on the sea bed at a depth of 10 m below the net pens used for fish culture. The a bility of a Capitella population to decompose organic matter may be ap plicable to the treatment of organically polluted sediment that accumu lates below the fsh farms.