Assessment of coastal anthropo-ecological system dynamics in response to a tsunami catastrophe of an unprecedented magnitude encountered in Japan

On 11 March 2011, a catastrophic earthquake and subsequent tsunami hit the Pacific coast of northern Japan, devastating many of the towns, villages and coastal ecosystems located along the shoreline. To assess the impacts of the disaster, we investigated temporal dynamics of fish and epibenthic megafaunal community structure in relation to changes in a range of physical, biological and anthropogenic variables between 2007 and 2018 in Onagawa Bay. Commercially important fish such as greenlings, Japanese anchovy, flatfishes, rockfishes were consistently abundant in both larval and adult fish assemblages. While abundance, species richness, and Shannon index H′ for adult fish and epibenthic megafaunal assemblages increased significantly soon after the disaster to peak values towards the end of the study period, the same metrics did not change accordingly for larval fish assemblages. Temporal dynamics of larval fish community clearly demonstrated significant seasonal variation along with changes in large-scale environmental conditions such as temperature and nutrients. However, anthropogenic components such as decline in human population, reduction in fishing pressure and the recovery of aquaculture operations significantly explained the observed post-disaster change in adult fish and epibenthic megafaunal communities. The pelagic and benthic components of Onagawa Bay appeared to have responded to the 2011 disaster very differently, and this study suggests the post-disaster recovery and dynamics of the coastal ecosystems may be regulated by how human societies respond to the impacts of a tsunami catastrophe through their influences on benthic habitat of ecosystems.