Colonization of the Restored and Newly Created Tidal Flats by Benthic Animals in the Sanriku Region of Northern Japan

Abstract

Tsunamis and subsidence caused by the Great East Japan Earthquake in 2011 created and restored some intertidal areas along the Sanriku coastline of northern Japan. Otomo-ura is one such area in Iwate Prefecture. The tidal flat of Otomo-ura had been reclaimed for farmland 50 years prior but has “returned to the sea” after the tsunamis. Our 3-year-long qualitative and quantitative investigation of benthic fauna after the tsunamis reveals that a variety of animals have quickly colonized the newly created habitat. In August 2012, 2013, and 2014, the number of species observed was 27, 51, and 59, respectively. Rapid colonization was also observed for another newly created habitat in the Unosumai River estuary, which is situated about 40 km north of Otomo-ura. We find that that habitat heterogeneity between the peripheral and central areas and microhabitats provided by primary (e.g., sand and cobbles) and secondary substrates (e.g., oyster’s and algal bodies) both contributed to increased species richness and population density. Although direct-developing species, which lack planktonic larval stages, had hardly been expected to colonize the restored and newly created vacant tidal flats, a direct-developing gastropod Batillaria attramentaria has been observed in Otomo-ura since August 2014. Colonization by the direct-developing gastropod and DNA analyses for 15 populations, including one from Otomo-ura, indicate that regional management of source populations will be necessary to prevent colonization by Euspira fortunei, another direct-developing alien predator, and to diminish the effects of parasitic Perkinsus on the host clam population.