Short-Term Effects of the March 11, 2011, Tsunami on Phytoplankton Assemblages in Ofunato and Kesennuma Bays, Japan

We investigated the changes in phytoplankton quantity and diversity after the March 11, 2011, Tohoku earthquake and tsunami in Ofunato Bay and in the mouth of Kesennuma Bay in northeastern Japan. Phytoplankton quantities increased in Ofunato Bay, and diversity changed. The phytoplankton assemblages other than diatoms increased near the water surface after the earthquake. In contrast, a clear change was not observed at Iwaisaki, at the mouth of Kesennuma Bay, during the survey. These results suggest that the influence of the tsunami on phytoplankton varied by location. In this study, phytoplankton in Ofunato Bay were affected by the tsunami, which is enclosed and was easily affected by the terrestrial environment and broken seawall. Limited changes were observed at Iwaisaki at the entrance to Kesennuma Bay.