Spatial distribution patterns of macrobenthic communities during winter and summer in the Masan Bay special management area, southern coast of Korea

Abstract

The spatial distributions of macrobenthic communities in Masan Bay were investigated during summer and winter, 2004. A total of 104 species were sampled with mean density of 448 ind./m2 and biomass of 77.1 g/m2 in winter. In summer, a total of 107 species occurred with 485 ind./m2 and a biomass of 94.5 g/m2. The most dominant species in winter were Paraprionospio pinnata (24.2%) among polychaetous worms and Theora fragilis (14.1%) among molluscs, but they were replaced in summer by Prionospio cirrifera (20.4%) and Lumbrineris longifolia (14.5%). The difference in species composition and abundance of benthic communities between the two seasons was due to the hypoxia in the bottom layer of the inner bay during summer, which defaunated the macrofauna of the sediments. In the winter when DO concentration increased to normoxia, the pelagic larvae of benthic fauna settled in the soft sediments, but there was a spatial gradient in values of total biomass, density, and H' and benthic pollution index (BPI); higher values were found toward the mouth of the bay. The multivariate analyses like the cluster analysis and MDS ordination showed that Masan Bay could be divided into two or four stational groups in winter and summer whether the hypoxia occurred or not. Group I consisted of sites at the inner bay and central area and Group II, sites at the bay mouth. In summer the inner bay area could be further divided into the shallow impoverished area and the deeper abiotic one.