Long-term variations of the macrobenthic community diversity (species number) in the Chokchon macrotidal flat, Incheon, Korea

초록

Long-term monitoring becomes more important in assessing the ecological change. To understand the causes of temporal variation of tidal flat macrobenthic community and forecast its future, we established three stations in the Chokchon macrotidal flat, Incheon, Korea. Sampling program started from May, 1989 and ended, for the two fixed stations in the upper and mid-intertidal zone due to reclamation, in Nov., 1996, and for the one in lower zone in Nov., 2001. Biological samples with a surface area of 1㎡ were bimonthly obtained at each station. A decomposition method, which assumes additive relationship among seasonality, trend and cyclical variation, was employed for time-series analysis of species numbers of macrobenthic community. Species number showed strong seasonality (≳ 95 % of total variance) and lowered in warmer seasons (May, July and September). In trend analysis, diversity synchronized from 1989 to 1994, but a departure occurred at the upper station in 1995 and 1996. However, a notable increase in the species number continued all the way from 1989 to 2001. Based on the regional comparison of seasonal variations of macrofaunal community with those in the different climate regime, the cause of the lower species number from late spring to early autumn observed in this study was estimated to be due to the steady heavy rain in the rainy season. The general increase in macrobenthos diversity was related to the variation with surface seawater temperature, precipitation, substratum property (mean grain size of surface sediment, phi) and organic matter (ignition loss, %); and it seemed to be affected by the temperature rise in the former period (1989-1995) and by eutrophication in the latter period (1997-2001).