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

Abstract

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.