Influence of different types of sessile epibionts on the community structure of mobile invertebrates in an eelgrass bed

The variation in the biomass, abundance and diversity of mobile invertebrates in eelgrass ( Zostera marina ) beds has been examined in relation to various abiotic and biotic factors, such as water temperature, salinity, eelgrass biomass and epiphytic microalgae presence. However, the importance of sessile epibionts, such as macroalgae and calcific spirorbid polychaetes attached to eelgrass blades, has not been the focus of previous studies. In the present study, we examined the effects of three different sessile epibionts, namely, branched red algae, filamentous green algae, and calcific spirorbid polychaetes, on the biomass and diversity of mobile invertebrates in the eelgrass beds of Akkeshi in Northeastern Japan. The relationships of the dominant mobile invertebrate biomass, the total biomass of mobile invertebrates and the species diversity to multiple abiotic and biotic variables were analyzed using a linear mixed model. Our results show that large-sized epibiotic organisms can be good predictors of the variation in the total biomass, species richness and species diversity of mobile invertebrates and the biomass of major dominant species, especially for species that have a relatively high dependency on eelgrass blades. These results suggest that the different functional groups of sessile epibionts have significant roles in determining the biomass and diversity of mobile invertebrates in eelgrass beds.