Search

The Yatsushiro Sea is an inland sea in the southwestern part of Kyushu Island, covering an area of 1,200 km, 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. [ABSTRACT FROM AUTHOR]

Abstract In this report, we describe the first discovery of two living ostracods from the Japanese archipelago, Sinocytheropteron ignobile and Sinocytheridea impressa , which are typically continental faunal elements from China, during our research on the distribution of ostracod assemblages in the Ariake and Yatsushiro Seas in southwest Japan. The (palaeo-) biogeographical data from recent and fossil records indicate that S. ignobile and S. impressa migrated through land bridges during past decreases in sea levels. We also discovered Xestoleberis ryukyuensis , which has been reported from the Ryukyu Islands; its discovery in our study area indicates the current northernmost distribution of the species and suggests that it migrated from the Ryukyu Islands to the study area using the Tsushima Warm Current, a branch of the main Kuroshio Current. This evidence suggests that the migration of shallow-marine ostracods between the continents and their adjacent islands affect not only global oceanic current but also global decreases in sea levels and the (palaeo-) geography of adjacent seas. Thus, ostracods living within the continental coasts provide powerful evidence for reconstructing the connection between the continent and its adjacent islands. Highlights • A total of 155 ostracode species were identified from the Ariake and Yatsushiro Seas. • We discovered living specimens of two Chinese continental taxa. • These Chinese continental taxa do not transported by oceanic current. • The continental taxa living in Japan migrated there during past geological periods. [ABSTRACT FROM AUTHOR]