Effects of the Great East Japan Earthquake on Intertidal Macrobenthos in Iwate Prefecture

Abstract

To determine the effects of the Great East Japan Earthquake and resulting tsunamis on the distribution of marine benthic macrofauna throughout Iwate Prefecture, the fauna of three tidal flats was compared before and after this catastrophic event. Because this prefecture has a history of tsunami events, floodgates and seawalls were established along its coastline following the tsunami in 1933 as a disaster prevention strategy. Consequently, the intertidal environment throughout the region had been already modified before the 2011 tsunamis. Despite this former loss of habitat, a number of benthic invertebrates occurred in the tidal areas before the intertidal disturbance due to the 2011 tsunamis. More importantly, 52–76 % of taxa of benthic invertebrates previously recorded in this region were found in the tidal area after the tsunamis’ disturbance. Additionally, several taxa that are considered threatened (according to the Japanese Association of Benthology) appeared in these and newly created tsunami-flooded habitats after 2011. Our data suggest that the marine macrobenthos in this region, including these threatened taxa, were tolerant of the tsunami disturbance or comprised opportunistic taxa capable of rapidly colonizing new habitats. However, the recovery patterns of benthic invertebrates varied across sites: remarkable reduction of tidal flat decreased its biological diversity, but creation of new tidal habitats strikingly increased taxa richness. The reconstruction of coastal structures should be planned considering preservation of the remaining and newly created tidal flats. Future disaster risk management should take into consideration both the maintenance costs of these structures and the effects they have on biodiversity and ecosystem functioning in intertidal flats.