Ecological Responses of Macrobenthic Communities in Tidal Flats to Disturbances by the Great East Japan Earthquake

We investigated changes in taxon richness and composition of macrobenthic communities for four successive years after the tsunamis caused by the Great East Japan Earthquake at six intertidal flats in Sendai Bay, where monitoring had been ongoing before the tsunami. The field surveys showed that although taxon richness decreased in most of intertidal flats immediately after the tsunami struck, it subsequently increased within 1-2 years due to the colonization of many taxa, including those that had not existed in these tidal flats before the tsunamis. However, by 2014 (i.e., 4 years after the tsunami), taxon richness had decreased again to pre-tsunami levels. In addition, taxon composition was close to that found before the tsunami struck, especially in intertidal flats that were subjected to large disturbances by the tsunamis. Thus, a number of opportunistic taxa that had not been observed previously appeared after the Great East Japan Earthquake, but gradually decreased as the community structure recovered. This study also suggests that taxon composition of the macrobenthic communities changed year to year to some extent regardless of the tsunami disturbance. Our findings imply that since macrobenthic communities in intertidal flats are somewhat dynamic, they are not likely to attain the exact same structure as before the tsunamis, even though taxon composition is largely shaped by site-specific environmental conditions.