In April 1997, the inner part of Isahaya Bay was shut off from Ariake Sea, western Kyushu, Japan with a dike for reclamation. After this isolation, in the both inner and outer parts of Isahaya Bay, aspects of water quality suddenly changed, and fauna of bivalves was drastically replaced. In the outer part of Isahaya Bay, 25 species of bivalves were collected from the 20 fixed stations in June 1997. However, the number of species and the mean individual density suddenly decreased starting November 1998, and then increased after November 2000. These phenomena are synchronized with the temporal change of the dissolved oxygen in this area. In the inner part of Isahaya Bay, 11 species of marine bivalves were collected in large numbers before the dike was completed. These species were still alive in May 1997, but most of them had died by August 1997, when salinity decreased to <5psu. However, an introduced species, Potamocorbula sp. that was not found prior to the isolation of this bay, replaced the pre-isolation bivalve community since August 1997. This species also increased in number in Saemangeum, western Korea, after the dike construction, and in San Francisco Bay, USA as an exotic species. Therefore, it can survive and multiply alone through large environmental changes such as isolation and artificial introduced. Fossils of this species were also found from several horizons in Holocene deposits in southwestern Japan. These fossils occur only in a monospecific shell bed, and some marine bivalves occur below this shell bed. Therefore, the aggregation of Potamocorbula shells is essential to the reconstruction of environmental changes, such as isolation.
|Number of pages||10|
|Publication status||Published - 2004 Sep 1|
- Ariake Sea
- Isahaya Bay
ASJC Scopus subject areas