Repercussions of the Great East Japan Earthquake tsunami on ellipsoidal Alexandrium cysts (Dinophyceae) in Ofunato Bay, Japan

Abstract

Shellfish aquaculture in Ofunato Bay, Northeast Japan, was seriously damaged by a tsunami generated by the Great East Japan Earthquake, March 11th, 2011, accompanied by paralytic shellfish poisoning (PSP) outbreaks caused by Alexandrium tamarense (Dinophyceae). To understand longer future trends of PSP, an investigation was made of the historical occurrence and causes of Alexandrium outbreaks after the tsunami. Vertical distributions of Alexandrium cysts in two sediment-cores from Ofunato Bay revealed that the sediments above ca. 25 cm were eroded, re-suspended and re-deposited, and they included unusually abundant Alexandrium cysts. This abundance of cysts was due to re-deposition of older sediments by the tsunami. The first Ofunato Bay PSP incident was in 1961 after the Chilean Earthquake tsunami and was probably caused by similar unusual blooms of Alexandrium germinated from older sediments as the Great East Japan tsunami, together with nutrient enrichment because of population increase at the start of shellfish aquaculture.

Influence of Seismic Loads Considering Soil Properties and Wave Passage Effect on the Seismic Response of a Multi-Span PSC Girder Bridge

“…When evaluating the dynamic response of a bridge during an earthquake, the most important factor to be considered is the seismic load acting on the bridge. Prior studies were conducted experimentally or analytically by applying seismic waves obtained from earthquakes such as El Centro, Ofunato, and Hachinohe to structures [24][25][26][27]. However, each real seismic wave has its own characteristics, which may cause different results depending on the natural frequency of the structure [28].…”