Spatiotemporal changes in meiofaunal composition on soft substrates in the semi-enclosed inner section of the northern Yatsushiro Sea

摘要

The Yatsushiro Sea is an inland sea in the southwestern part of Kyushu Island, covering an area of 1,200?km2, and is partly connected to the Ariake Sea to the north and the east China Sea to the south. The innermost part of the sea is semi-enclosed by the Shiranui reclaimed land, which was created in 1967. Coastal fishery operators in the region have suggested that fish stocks have declined due to the accumulation of ‘hedoro’ (sludge) on the sea floor, which increased after the land was reclaimed. This project analyzed spatiotemporal changes in the community structure of the meiofauna, which represent ideal organisms for environment assays and in the environmental factors in sediments at four fixed stations around the inner part of the northern Yatsushiro Sea over 3?years (May 2010–February 2013). The results confirm the site of local deposits in the narrow sub tidal section off the Shiranui reclaimed land, where rich organic matter has accumulated and highly sulfidic conditions above the standard criterion value for fisheries were present, along with clear and significant decreases in meiofaunal abundance during the summer. Multivariate analyses, however, did not reveal any strong association between the meiofaunal composition and any environmental factor in sediments, suggesting the organic and sulfidic conditions were not driving the temporal changes in meiofaunal structure in the area. Instead, the meiofaunal changes could be directly related to the low continuous decline in dissolved oxygen and salinity in the water on the sea floor in summer.