Physicochemical factors affecting goby fauna in the intertidal zones of temperate riverine estuaries of the Seto Inland Sea

Estuaries are important environments for the sustainable use of natural resources; however, these coastal areas are deteriorating continuously owing to anthropogenic impact, and thus their conservation has become a global issue. This study aimed to identify the physicochemical factors that influence goby fauna and richness, which have high species diversity in temperate riverine estuaries, by conducting field surveys. We collected gobies and measured six physicochemical factors (median particle size; percentage of gravel, sand, and mud; salinity; and elevation) in the intertidal zone of two riverine estuaries flowing into the Seto Inland Sea of Japan. Twenty-six species of gobies were found at 191 sites during our surveys. To classify the survey sites by goby fauna, we stratified 132 sites, where more than two species of goby were found, into seven groups by using two-way indicator species analysis. The results of canonical correspondence analysis and classification and regression tree suggested that the goby fauna changed along these physicochemical environmental gradients. In particular, sediment characteristics might be an important factor that influences the goby fauna. However, no relationship was found between species richness of gobies, as revealed by the result of generalized linear mixed model. Therefore, our data indicate that species diversity of gobies utilising various environments cannot be maintained by conservation of a specific environment in riverine estuaries. The diversity and heterogeneity of the physicochemical environments, especially sediment conditions, need to be maintained and controlled for the conservation of the gamma diversity of estuarine goby.