Distribution of Macrobenthic Mollusks in the South Sea and Around Jeju Island, Korea

초록

The composition and seasonal variation of mollusk fauna were investigated in the shallow water soft bottoms of southern seas from May 2009 to February 2012 within the framework of a national survey of the coastal ecosystems in Korea. The macrobenthic samples were seasonally collected from 86 stations from Jindo to Busan and around Jeju Island using van Veen grabs. During the study period, a total of 243 species of mollusks were found, including 114 species in the class Gastropoda, 111 in the class Bivalvia and 18 in other mollusk classes. The average density and biomass were 212 individuals m-2 and 46.6 g m-2 respectively. However, seasonality did not have a significant effect on the distribution of mollusks. The southern seas in Korea showed overall macrofaunal diversity similar to the mollusk diversity in the west sea, but higher biomass and less abundance were found. Based on cluster analysis of their composition and abundance data, the study area was clearly divided into three regions, the South Sea, Jeju Coast and Ieo-do area. The first group of the South Sea was characterized by the highest biodiversity with the sediment type of medium silt facies. It was again subdivided into four different faunal subgroups. The macrobenthic molluscan communities around Jeju Island were recognized by the environmental characteristics of fine sand facies with intermediate diversity. In contrast, the molluscan diversity around Ieo-do was lowest, with the sediment characteristic of coarse silt facies. The distribution of mollusks in the study area was primarily dependent on sediment types such as mean grain size, together with other bottom characteristics of depth, dissolved oxygen and CaCO3 contents of sediment. In addition, the major dominant species in the South Sea and around Jeju Island were Cycladicama cumingii, Ennucula niponica, Theora fragilis, Moerella jedoensis, and Thracia seminuda based on frequency of presence and density.