Primary productivity in coastal ecosystem supports various components of marine biodiversity and ecosystem functions. This affects not only higher trophic levels in the pelagic layers, but also benthic consumers including important fisheries targets (e.g. bivalves, decapod crustaceans). Coastal ecosystems are affected by oceanic dynamics, terrestrial input and geographical (topographical) structures, which make spatial variation in communities and production greater and more complex than offshore pelagic ecosystems. Eastern Hokkaido is predominantly influenced by Coastal Oyashio Water (COW) which brings low temperature and low salinity. Spring phytoplankton blooms occur every year in the COW, supporting high productivity and ultimately various seafood resources. Although the extent of global coastal wetlands is seeing overall declines due to various anthropogenic activities, pristine freshwater/brackish wetlands remain in eastern Hokkaido. These buffer against the direct river discharge of terrestrial matter through rivers. Continued protection and conservation of wetlands may benefit coastal productivity and sustainability. Therefore, surveys of areas that have coastal wetlands are important.
The main objective of this article is to examine spatial variation of diatoms along nearshore areas of Biwase and Hamanaka Bays that are implied to display terrestrial effects from Kiritappu Wetland, Eastern Hokkaido. We conducted in situ surveys measuring seawater temperature, salinity, nutrients concentration, and colored dissolved organic matter (CDOM) absorption as indicators of wetland-influenced river discharge at the surface to investigate the spatial variation in abiotic coastal water properties in nearshore areas. In addition to observations on diatom taxa composition, we measured both total and size-fractionated chlorophyll (Chl) a concentrations to act as biotic environmental factors of the study area.