Hisao Sasaki

Impacts of Fuel Spills Caused by the Great East Japan Earthquake and Tsunami on the Subtidal Soft-Bottom Communities of a Semi-enclosed Bay Located on the Sanriku Coast

We assessed the ecological consequences of the fuel spills and the subsequent conflagration that resulted from the tsunamis caused by the Great East Japan Earthquake. Analyses were performed at a range of subtidal stations (water depth: 8.2–37.2 m) located in Kesennuma Bay, Japan, during the period 2011–2014. The sediments contained high concentrations of polycyclic aromatic hydrocarbons (PAHs) (mean total PAH concentrations: 18,023–89,197 μg kg−1 dry weight). Most PAHs in the sediment of the inner bay (57–82 %) were derived largely from petrogenic sources, but at other stations most (55–86 %) had pyrogenic origins. Levels of petrogenic PAHs decreased more rapidly than those of pyrogenic PAHs over 4 years, possibly because of microbial degradation. PAH contents in the sediments peaked at 8–15 cm depth and were much reduced near the sediment/water interface. The macrozoobenthic community was largely dominated by opportunistic polychaetes; other taxa, including amphipods and bivalves (but not Theora fragilis), were less abundant. The PAHs often exceeded the effects range median (ERM) in US Sediment Quality Guidelines, indicating elevated ecotoxicological risk levels for the benthic invertebrates. Nevertheless, negative impacts of PAHs were not detected in the dominant macrozoobenthos. Thus, the dominant taxa were potentially tolerant to PAH pollution. Sediment in the bay currently contains high levels of PAHs, especially in thesubsurface layer. Therefore, long-term monitoring is required to fully understand the ecological consequences (for the coastal soft-bottom communities) of the 2011 fuel spill and subsequent conflagration.

Damage to seagrass and seaweed beds in Matsushima Bay, Japan, caused by the huge tsunami of the Great East Japan Earthquake on 11 March 2011

ABSTRACT Damage to seagrass and seaweed beds caused by the huge tsunami of the Great East Japan Earthquake on 11 March 2011 was investigated in Matsushima Bay, Miyagi Prefecture, Japan, by comparing satellite images taken before the tsunami in November 2009 and after the tsunami in May 2011. The results showed that the tsunami destroyed 220 ha of seagrass and seaweed beds, from 320 ha in 2009 to 100 ha just after the tsunami. Zostera marina beds on the sandy and muddy bottom were rather severely damaged compared with brown seaweed beds of Sargassum horneri on the rocky substrate. Substrates of the beds and directions of the tsunami seem to be responsible for the magnitude of the damage to the beds. Maps of the spatial distributions of the beds before and after the tsunami can provide information for the restoration of seagrass and seaweed beds as natural infrastructures of coastal fisheries resources.