Macrobenthos compose the dominant biomass in marine sediment and play an important role in the maintenance of the benthic environments through the bioturbation actions. The benthic environment easily affect benthic organism distribution because of high organic contents of sediment. In this study, we investigated the differences of macrobenthos distribution along the environmental characteristics at the mudflat of the Sapjin Industrial complex. The study area are located in the mouth of Muan bay, where in the same geographical position. Six stations were selected and two season surveys were conducted in the autumn 2015 and the spring 2016. Station 1, 2, 3 adjacent to Sapjin Industrial complex and a discharge of an out full from Mokpo sewage treatment plant and station 4, 5, and 6 in the Shinan area located apposite of Mokpo area. At each station, three repeat sampling were made using a bottom sampler (0.3m2), sieved on a 1 mm mesh and fixed (10% buffered formalin). Macrobenthos were then sorted, identified to the lowest tractable taxonomic group and counted. Sediment samples in each station were obtained for grain size analysis and organic matter content. Characteristics of the distribution were investigated, and the correlations of organic matter content in sediment with macrobenthos compositions were assessed using the PRIMER program.
The sediment particle size in Mokpo area consist of slightly gravelly mud (gM) and mud (M) with average particle size 6.97, whereas in Shinan area consist of slightly gravelly muddy sand (gmS) and slightly gravelly mud with average particle size 5.25. Sediment TOC was recorded 0.95% in the autumn and 0.92% in the spring at Mokpo area, and 0.33% in the autumn and 0.31% in the spring at Shinan area. Total number of species were 29 in the autumn and 26 in the spring at Mokpo area, and 14 in the autunm and 12 in the spring at Shinan area. The major density dominant phylum were Mollusca at the Mokpo area, while Polychaete at the Shinan area. The pollution indicator organism Musculista senhousia was dominant species at the Mokpo area. Ecological indices were higher at Mokpo area during both seasons. M1 and M3 in the Mokpo (group 1) area and S2 and S3(group 2) in the Shinan area clustered together with 70% similarity. M2 and S1 did not cluster with the other stations, however, M2 showed similarity to group 2. Evenness had significant positive correlation with silt concent, and diversity with ignition loss. The dominant species was clearly divided into two areas correlated with sediment TOC.