Ecological impacts of the 2011 Tohoku Earthquake Tsunami on aquatic animals in rice paddies

The 2011 Tohoku Earthquake Tsunami hit the Pacific coast of eastern Japan on March 11, 2011 and disturbed various ecosystems, including rice paddies along the coast. In Miyagi Prefecture, located in the Tohoku Region, a total of 12685 ha, or about 11.5 % of the rice paddies, were inundated and damaged by the tsunami. Although rice paddies are artificially constructed, they have long been used by many kinds of aquatic animals as habitats. To assess impacts of the 2011 Tohoku Earthquake Tsunami on aquatic animals inhabiting the rice paddies, census surveys were conducted at inundated and non-inundated rice paddies at six sites along the coast of Miyagi Prefecture from June to July 2012. This was 30-60 days after the first transplanting of rice seedling in inundated rice paddies following the tsunami. In the surveys a total of 100 aquatic animal taxa, 72 from inundated and 86 from non-inundated rice paddies, were found. Although the taxonomic richness and composition differed among the sites, the total number of observations of walk dispersers and obligatory aquatic animals without resting stages were significantly lower in inundated than in non-inundated rice paddies. However, no notable difference was detected in taxonomic richness and the total number of observations of flight dispersers and obligatory aquatic animals with resting stages between inundated and non-inundated rice paddies. The results showed that the tsunami had a substantial impact on freshwater animals but that restoration of the paddies for rice cultivation enhanced rapid recolonization by aquatic animals with high dispersal abilities and resting stages.