Distribution and abundance of bivalves in relation to the bottom condition of tidal flats in the northern part of the Ariake Sound [Japan]
2005
Hishiki, K.(National Fisheries Univ., Shimonoseki, Yamaguchi (Japan)) | Suda, Y. | Koshiishi, Y. | Murai, T.
To elucidate the relationship between distribution of bivalves and sediment conditions, this study was carried out in the_northern part of Ariake Sound from June 2002 to October 2003. The bottom samples were collected from the nearly sandy and muddy bottoms in a tidal flat. Sediment characteristics such as mud content, AVS-S and I.L. were analyzed and bivalves in the mud samples were sorted and identified. Pooled mean values (2002 and 2003) of these sediment characteristics were significantly higher (p0.01) in the muddy bottom than in the sandy bottom. The mud content increased significantly (p0.01) from 2002 to 2003 in both bottoms. Total number of bivalves collected in the entire survey period was 11303 including 8 families and 11 species. The numerically dominant species were Ruditapes philippinarum, Modiolus metcalfei and Scapharca subcrenata which accounted for about 99% of all collected individuals. The highest number of species was recorded in the muddy bottom in 2003, when mud content was highest. While, the highest number of individuals was recorded in the sandy bottom in 2002, when mud content was lowest. R. philiapinarum was the dominant species in the sandy bottom in 2002, when mud content was about 10%. When mud content was about 20%, M. metcalfei was the most dominant species. S. subcrenata became the most dominant species when mud content increased up to 50%. These results indicate that there is a clear relationship between distribution of bivalves and sediment conditions and the increase in mud content of the bottom sediment may be one of the factors responsible for declining abundance of R. philippinarum.
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