Eelgrass (Zostera marina) forms extensive beds in coastal areas and provides valuable ecosystem functions. Eelgrass beds could be affected by various types of abiotic and biotic factors differently across regions and also by environmental gradients within each system. Spatial comparison of the functions would give insights into the value of ecosystem services by eelgrass beds. In this study, we conducted a field survey in Akkeshi-ko Estuary and Saroma-ko Lagoon in Eastern Hokkaido to evaluate the variability in their ecosystem functions. Our main objectives are 1) to quantitatively assess the variation in primary productivity (represented by eelgrass aboveground and epiphytic microalgae biomass) and secondary production (epifaunal abundance and biomass), and 2) to examine the responsible abiotic and biotic factors for the observed variation in ecosystem functions.
　Overall, variables representing primary and secondary productions differed significantly between the two regions and within each region along environmental gradients. The linear mixed model showed that abiotic factors such as water nutrients and temperature explain the variation in plant traits and that both abiotic and biotic factors affect variation in the animal abundance and biomass. The results demonstrate complex interactive effects of multiple environmental factors on eelgrass ecosystem functions that operate at different spatial scales.