Abstract
A faunal investigation of the Tokachi coastal land-locked lagoons in Hokkaido, northern Japan was carried out in November 1996 to detect changes in the benthic communities and lagoon environment compared with a study done in 1942, and to examine the relationship between the benthic community structure and lagoon environment. The macrobenthic fauna of these lagoons were composed of species typical of Japanese oligo- and mesohaline brackish-waters. Multivariate analysis revealed a significant positive correlation between the community structure and some particular environmental variables, i.e., salinity and sediment particle size, which are the most important proximate factors in the community organization of brackish-water benthic species. The macrobenthic communities and their structural characteristics in the lagoons showed no drastic changes since the 1942 study. However, the low density of the bivalve Corbicula japonica and the distributional changes in the dominant polychaete species in this study indicated the peculiar conditions of these land-locked lagoons that may cause population fluctuations and the occasional dispersal event among the lagoons. The description and recognition of the biodiversity of brackish-water fauna is indispensable to conserve the brackish-water environment, moreover, the knowledge of the characteristics of the habitat structure of brackish-water and of the genetic structure of brackish-water species in recent years calls for new insights in future research.
