Community Structure of Macrobenthos in the Subtidal Soft Bottom in Semi- enclosed Youngsan River Estuarine Bay, Southwest Coast of Korea

Investigations were made on the community structure of macrobenthos in the subtidal soft bottom around semi-enclosed Youngsan River estuarine bay, southwest coast of Korea during the period from April 1995 to February 1996. Three macrobenthos samples were collected at 40 stations using a van Veen grab(0.1 m^2) during the study period. A total of 206 species of macrobenthos was identified. Their mean density and biomass (wet-weight, wwt) were and , respectively. Of these, there were 74 species of polychaetes (), 60 molluscs (), 51 crustaceans () and 21 miscellaneous taxa. Molluscs were represented as a density- and biomass-dominant faunal group with a mean density of ( of the total benthic animals) and biomass of ( of total biomass): It was followed by polychaetes with ( of the total density). Total number of species and diversity were Bow in the inner estuarine bay containing high mud content and organic matter, whereas they were high in the outer stations containing low mud content and organic matter. Major dominant species were one biralve, Theora fragilis and three Polychaetes, Tharyx sp., Poeciloceatus johnonni and Lumbrineris lontifolia whose mean densities were , , and , respectively. Cluster analysis indicated that the study area could be divided into four station groups: two innermost station groups, a central bay and an outer station group. The species diversity increased from the inner station group toward the outer groups. These results were discussed in terms of both the environmental factors and distribution of benthic community.