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 extensively 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 themselves. During the summer, the bottom water in organically polluted areas is apt to be anoxic. High levels of hydrogen sulphide are often produced in the organically polluted sediment. We have attempted to treat the organically polluted sediment by exploiting the biological activities of a deposit-feeding polychaete, Capitella sp. I. In experiments in the laboratory, the size of colonies of this species increased very rapidly, and the organic matter that was loaded on the sediment was very efficiently decomposed. The proliferating colonies also promoted the oxidation of the reduced sulphides in the sediment. The results of this study indicate that dense patches of more than 59 000 individuals m-2 have the potential to exhaust the organic matter loaded on the seabed at a depth of 10 m below the net pens used for fish culture. The ability of a Capitella population to decompose organic matter may be applicable to the treatment of organically polluted sediment that accumulates below the fsh farms.