The shelter effect is one of the important functions of seagrass bed suggesting that seagrass complex structure decreases predation risk to small animals. However, predation is known to regulate epifaunal community. Previous studies have not investigated enough on seasonal and spatial variation of top-down effect among different functional groups of epifauna.

We examined this problem by predation rate assay in the eelgrass beds in Akkeshi, Hokkaido at 2 sites in 2 seasons, 2014. In this assay, predation rate was assessed by a tethering experiment using 3 kinds of prey; an amphipod (Ampithoe lacertosa) that is highly mobile, a snail (Barleeia angustata) that is less mobile, and dry squid that has no mobility. Prey was moored in the eelgrass beds by line, and the presence/absence was recorded after 24 hr. Results of this experiment showed that predation rate on A.lacertosa varied seasonally, and that of dry squid varied spatially, while that of B.angustata was no variation.

The difference between the results of amphipod and dry squid indicates that the behavior of epifauna, to hide in the complex structure, may play an important role for this results.