Impacts of the 2011 mega-earthquake and tsunami on abalone Haliotis discus hannai and sea urchin Strongylocentrotus nudus populations at Oshika Peninsula, Miyagi, Japan

ABSTRACTOn 11 March 2011, a massive tsunami generated by amega-earthquake with a moment magnitude of 9.0 hita wide area of Pacific coast of northeast Japan. Weobserved and analyzed the effects of the earthquakeand tsunami event on populations of the abaloneHaliotis discus hannai and sea urchin Strongylocentrotusnudus at Tomarihama in Miyagi, where we have car-ried out regular surveys since January 2008. Before theevent, algal forests dominated by the brown macroalgaEisenia bicyclis had developed in the survey area shal-lower than 5 m in depth, where adult abalone>50 mm in shell length (SL) inhabited. Juvenileabalone 50 mm SL, mainly inhabiting the algal forests, wasreduced by more than half. The impact of the tsunamiwas more profound in the CCA area than in themacroalgal forest. Juvenile abalone and urchins largelydecreased to 14 and 5% of the densities just before theevent, respectively. The distribution pattern of juve-nile abalone and urchins could be a cause of themarked decrease, because most of these animalsinhabited the CCA area where the disturbance by themassive water movement was not reduced by theeffects of the macroalgal forest.Key words: benthic community, marine invertebrates,mortality, physical disturbanceINTRODUCTIONOn 11 March 2011, the Great East Japan Earthquakeoccurred off the Pacific coast of northeastern part ofHonshu Island Japan with a moment magnitude of 9.0at a depth of 24 km. The massive tsunami generatedby this earthquake severely impacted the coast ofnortheastern Honshu Island and resulted in the loss ofnearly 19 000 people and devastated many towns inthe coastal areas of this region. Fisheries are one of themost important industries in the coastal area impactedby the tsunami, and the population depends on thehigh production of marine resources and the sustain-able condition of marine ecosystems. Rapid assess-ments are needed to evaluate effects of the earthquakeand tsunami on coastal ecosystems and populations offishery resource organisms for the future fishery andstock management in the area.Tsunamis are rare disturbance events for marineecosystems but they possess a high intensity and⁄orenergy, which have great potential to affect coastalbenthic communities (e.g., Lomovasky et al., 2011).Previous studies have described effects of tsunamis onmarine ecosystems, especially after the event of 26December 2004 that struck the coastline of tropicaland subtropical zone around the Islands of Sumatraand the Indochina Peninsula. In these studies, effectsof the tsunami on seagrass beds (Whanpetch et al.,2010), coral reefs (Chavanich et al., 2005; Kumarag-uru et al., 2005; Goffredo et al., 2007) and mangroves(Danielsen et al., 2005; Vermaat and Thampanya,2006) were described and analyzed. However, scien-tific evaluation has not been conducted on the effectsof such a massive tsunami on populations of importantfishery resources in temperate areas.On coastal rocky shore reefs in temperate areasaround the world, abalone and sea urchins are eco-logically and economically important species. Both