Spatial distribution and assemblage structure of macrobenthic invertebrates in a brackish lake in relation to environmental variables

The distribution of organisms relative to their habitat is of central importance to ecology. The nature of this distribution provides an initial insight into the types of ecological processes that regulate populations and assemblages. Estuaries provide diverse habitats in terms of spatial heterogeneity in physical and chemical conditions. The purpose of the present study is to determine the assemblage structure and the spatial distribution of macrobenthic invertebrates in relation to environmental variables in a brackish lake, Lake Hinuma, in Japan. Thirty-seven sites in the lake were selected to cover the entire area of the lake along gradients for water depth, salinity and median grain size of sediment. A total of 23 species and five higher taxa groups were found. In terms of total individuals, Corbicula japonica, Prionospio japonica, Notomustus sp. and Einfeldia sp. were the most abundant species. The results of cluster analysis and canonical correspondence analysis using 14 dominant species revealed that median grain size and salinity have significant effects on the spatial distribution of 11 macrobenthic species. That is, the two species C. japonica and P. japonica were found at sites with larger grain size and higher salinity, the six species Gradidierella japonica, Assiminea lutea japonica, Tylorrhynchus heterochaetus, Cyathura sp., Melita sp. and Potamilla sp. were found at sites with smaller grain size and higher salinity, the one species Einfeldia sp. was found at sites with larger grain size and lower salinity, and the two species Polypedilum sp. and Notomustus sp. were found at sites with smaller grain size and lower salinity. The results demonstrated significant differences in macrobenthic assemblage structures along environmental gradients in a brackish lake.