Molluscan assemblages along a bay coastline: Gradients related to geographical distribution and feeding habits of species
2007
Ohgaki, S.
Spatial variation in intertidal molluscan assemblage was investigated at 9 sites from outer to inner Tanabe Bay, central Japan. All the molluscan species were counted in 15, 50x50 cm quadrats at each site. Cluster analysis and PCA detected three distinct groups of sites in terms of species composition, i.e., the site outside bay, the sites around the bay mouth, and those in the innermost area. Diversity of the molluscan species decreased as the topographical openness of the sites decreased. Toward the inner reaches, southern species (35 deg N) and carnivorous species decreased, whereas northern species (31 deg N) and filter-feeding species increased in terms of the number of species, quadrats, and individuals. A similar trend is shown also by a review of previous surveys around Tanabe Bay. Analysis of the environmental parameters shows that winter water temperature is lower and chlorophyll a concentration is higher at the bay head than at the bay mouth, whereas the difference in salinity is not distinct between the two areas. A positive correlation between winter water temperature and abundance of the southern species is detected both along the bay coast and over a long time-span at fixed localities. Such a spatio-temporal correlation and other evidence implies the controlling effect of temperature and trophic regime of bay water on the pattern of the molluscan assemblages along the bay coastline.
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