Macrobenthos as Biological Indicators to Assess the Influence of Aquaculture on Japanese Coastal Environments

Owase Fisheries Laboratory, Mie Prefectural Science and Technology Promotion Center, Owase,Mie 519-3602, JapanAbstract: Todelineatepatternsinthegradientsofmacrobenthiccommunitiesaroundfishfarmsand to generate site-selection guidelines for sustainable fish farms, a quantitativesurvey was conducted in August–September 1998 and in February 1999 in fish-farming areas along the coast of Kumano-nada, central Japan. The biomass peakedin sediments containing 1.2 mg=g of total nitrogen or 9.2 mg=g of total organiccarbon, suggesting that these values are indicative of possible aerobic mineralizationof the loaded organic wastes. Macrobenthos was scarcely found in sediments withacid-volatile sulfides (AVS) >1.9 mg S=g, which suggests critical AVS conditions formaintaining sustainable and environmentally ‘‘friendly’’ aquaculture. An index,‘‘ED,’’ which serves as an index for bathymetry of the sampling site, was devised.EDwashighlycorrelatedwithfourcommunity parameters(biomass,density,speciesdiversity, and species richness) and with five environmental factors (sediment totalnitrogen, total organic carbon, total phosphorus and acid-volatile sulfides, andbottom-water dissolved oxygen). Compared with small-scale farms, environmentaldeteriorationanddeclineinmacrofaunawereobviousinlarge-scalefarms( 600 t=yrof fish production) that were located in inner parts of embayments and that hadcomparatively high ED values. However, in areas near open waters and thathad comparatively low ED values, the impacts of aquacultural activities were notclear. These findings suggest that the variation in macrobenthos and environmentalfactors found in the study area was attributable principally to the area’s bathymetryand, secondly, to aquacultural activities. Seven assemblages, recognized on the basisof cluster analysis, were placed in a gradient of ED versus fish production. Theseassemblages were classified into three groups: a group characteristic of a healthyzone, a group characteristic of a cautionary zone, and a group characteristic of