Characterization and spatiotemporal changes in the macrozoobenthic community structures at tidalflats along the Pacific coast of eastern Japan after the 2011 tsunamis using a large-scale survey data set

The macrozoobenthic community structure was examined at 21 sites along the Pacific coast of Japan, from Chiba to Aomori Prefectures after the 2011 tsunamis, using government survey datasets. The taxonomic diversity was low (20–42 taxa) in river-dominated sites on the Sanriku Coast, including Unosumaigawa and Orikasagawa in Iwate Prefecture. Endangered species were scarce at six sites along the Sanriku Coast (2–5 taxa) compared with the other 15 sites, including Aomori Prefecture (7–21 taxa). Cluster analyses based on the qualitative survey data classified the macrozoobenthic community types into four groups: (1) Low saline estuaries, (2) Sanriku Coast, (3) High saline inlets, and (4) Moderate saline estuaries. Qualitative analyses revealed that the community structure in Iwate Prefecture was typically characterized by marine andepifaunal organisms, such as limpets, gastropods, and barnacles, due to the steep, marine-affected, and substrate-rich river mouth habitats. Contrastingly, the quantitative survey data showed that the community structure at three sites in Iwate Prefecture was characterized by the highest diversity and density. Based on this survey, we listed 31 taxa that were absent from Iwate Prefecture, including 18 endangered species. This clearly showed that the macrozoobenthic community structure in Iwate Prefecture differed from those at other sites on the northeastern coast of Japan. Such discontinuity may partly be caused by the effects of cold Oyashio Currents in the Sanriku Region.