2019 年 73 巻 2 号 p. 84-101
To assess macrozoobenthic diversity and habitat conditions following the 2011 tsunamis, we conducted a series of field surveys in the Samegawa and Momiya River estuaries (Fukushima and Ibaraki Prefectures, respectively). We compared measured parameters with existing published datasets for 10 sites along the northeastern Honshu coast. Faunal diversity was higher at the Samegawa site (140 taxa in total, of which 31 were endangered and 51 were endemic; the faunal list included stenohaline marine taxa), likely because of the high habitat diversity at this location and seawater discharge from the thermal power plant. Cluster analysis differentiated distinct faunal community groupings associated with two habitat types: (i) marine-dominated sites, including the Samegawa Lagoon, Mangoku-ura, and Matsushima Bay and (ii) sites with riverine influence, including the mouths of the Samegawa and Momiya Rivers and brackish lagoons along Sendai Bay. The population size of the dominant mud snail Batillaria attramentaria in the Samegawa Lagoon declined steeply after the tsunamis but gradually recovered within five years. Microsatellite DNA analysis showed that the genetic diversity of this population did not significantly change following the tsunamis. After 2016, ongoing restoration work caused drastic habitat degradation at the Samegawa site, resulting in mass mortalities of polyhaline and stenohaline marine taxa and overall reductions in faunal diversity.
