Spatial Patterns and Temporal Succession in Macrobenthos Assemblages after the Dike Construction in Chonsu Bay, Korea

초록

Spatial patterns and temporal succession in soft-botttom macrobenthos assemblages were described for Chonsu Bay, a semi-enclosed bay, formed by a dyke constructed in 1984. About half of area was turned into a freshwater lake and reclaimed. The investigations were carried out seasonally between 1991 and 1995. Three replicate samples were taken at each station (15 stations) with a 0.1m2 van Veen grab. Bottom sediments consisted of mud close to the dyke, sandy mud in the central bay, and coarse sand in the mouth of the bay. A total of 273 species were identified. Number of species and densities decreased in the nothern part of the bay, adjacent to the dyke. The macrobenthos showed seasonal changes in species composition, range of distribution, and community delimitation caused by larval settling. Settling period in summer, unrelated to environmenatal conditions, added large number of juveniles in most of regions, but successful settlement has been a rare event locally. Theora fragilis (Bivalvia), Lumbrineris longifolia (Polychaeta), and Nephtys oligobrachia were numerically dominant, but their densities showed seasonal variation. Community structure of the macrobenthos in Chonsu Bay was affected by several environmental conditions, especially tidal current velocity, sedimentary facies altered by dyke construction, and irregular freshwater discharges from the lake with high organic matter content from neighboring fish farms. As a result, it is suggested that the coastal developments such as dyke construction had a localized effect continuously on the stability of macrobenthic communities for long times because of changing benthic environments.