Spatial Hierarchical Partitioning of Macrobenthic Diversity of Clam (ruditapes) Fishing Grounds over a Large Geographical Range of Japan

Studies on biodiversity management and conservation have often focused on tidal flats and estuaries. Macrobenthic assemblages in these habitats generally show local and geographical variations. Therefore, understanding about their spatial structure is important in assessing their biodiversity. This study aims to examine the spatial hierarchical composition of macrobenthic diversity inRuditapes philippinarumfishery grounds covering a large (1,700 km) geographic range of Japan. Four diversity measures according to the sensitivity parameterq= 0, 1, 2 and Inf were used to evaluate the contribution of four spatial levels (site, area, region and total). Observed assemblages had a few abundant and many rare taxonomic units. Although the abundant taxonomic units, includingRuditapes, occurred over larger spatial levels, the between-region beta diversity (diversity increment from the region to the total level) contributed most to the diversity of the total area. Comparisons of four diversity measures further revealed that the contributions of the between-region beta diversity were more pronounced in the rare taxonomic units than the abundant ones. Null model analysis confirmed these results although different null models generated some variations in the hierarchical composition of the diversities.