Organic Pollution in an Enclosed Bay on the Pacific Coast in Japan Judged from the Macrobenthic Community Structure

Abstract

Seasonal fluctuations of macrobenthic community structure were studied in Uranouchi Bay, Japan. In summer, there were no benthic animals in the middle and inner parts of the bay. Benthic animals were recolonized in winter. Dominant animal groups were polychaete worms and bivalves. Most of them were short-lived small animals and are the indicator species for organic pollution. This bay is enclosed, where culturing of yellowtails has been continued for more than 30 years. Therefore, the organic content in sediments is very high. It is also known that the oxygen depletion less than 10 % in saturation in bottom water occurs widely in summer. These facts on benthic community structure and bottom environmental conditions indicate that the organic pollution of this bay is very heavy. The improvement of the organic pollution in this bay will be performed only by the artificial topographic change to facilitate bay water mixing.