Ecological Consequences of the Tsunamis Caused by the Great East Japan Earthquake and Subsequent Disturbance Events in a Shallow Brackish Lagoon in Sendai Bay, Japan

The impacts of the tsunami caused by the Great East Japan Earthquake and subsequent disturbance events were examined in Gamo Lagoon, a shallow brackish lagoon in Sendai Bay, Japan. A major tsunami with a height of 7.2 m struck the lagoon on 11 March 2011, followed by a 2-month estuary closing and a typhoon-induced flood within a year. These events induced drastic changes in the salinity and sediment characteristics as well as a washout of vegetation. After the tsunami, the plant community was characterized chiefly by the proliferation of "pioneer species." The annual helophyte Suaeda maritima became dominant in the bare high-tide zone created through the disappearance of the reed marsh. Sand dune vegetation (SDV) had recovered only in patchily after 4 years, and the community was characterized by the invasive species Cakile edentula. The density and species richness of macrozoobenthos changed after each disturbance event (i.e., the tsunami, estuary closing, and typhoon). Macrozoobenthic density recovered within 6 months after the tsunami and typhoon, chiefly due to the density overshoots of several opportunistic taxa. Though tsunami-and typhoon-induced changes in macro-zoobenthic community structure were significant, by 3 years post-tsunami, the community had begun to recover toward pre-tsunami conditions. These results emphasize both the vulnerability and resiliency of estuarine biotic communities against large pulsed disturbance events.