Impacts of the Tsunami Disaster Caused by the Great East Japan Earthquake on the Benthic Communities and Their Recovery in Tidal Flats of Matsukawaura Lagoon, Soma, Japan

Abstract

Benthic communities and the physical properties of the bottom sediments were examined for 3 years after the Great East Japan Earthquake and subsequent tsunamis on 11 March 2011 at several sites of tidal flats in Matsukawaura Lagoon, Soma, Japan. The bottom sediments were changed mostly to sandy after the tsunamis except at some sites in the innermost parts of the lagoon, where the sediments became rather muddy due to the insufficient exchange of seawater. In 2011 just after the tsunamis, the species richness and abundance of benthic animals were almost halved compared with those before the tsunamis. However, a number of benthic species were recovered within 1 or 2 years after the tsunamis, although the species compositions of the benthic communities were temporally changed during the study periods. In particular, polychaetes showed early recovery while crustaceans, gastropods, and bivalves remained numerically far from recovery. According to census data collected for Matsukawaura Lagoon, many species inhabiting the tidal flats, including not only sessile and creeping species but also crawling and embedded species, could not successfully colonize in regions where embankments were rapidly constructed after the tsunamis in order to protect the farms and residential areas from future tsunamis. This study suggests that most benthic species have the potential to recover their populations rapidly after a tsunami if the seawater is well exchanged and the conditions of the sediment remain healthy. Thus, the conservation of potential habitats is essential to promote the recovery of benthic communities in this lagoon.