Transoceanic dispersal of the mussel Mytilus galloprovincialis on Japanese tsunami marine debris: An approach for evaluating rafting of a coastal species at sea.

Biofouled debris from the 2011 Great East Japan earthquake and tsunami has landed in the Northeast Pacific and along the Hawaiian Islands since 2012. As of 2017, >630 biofouled debris items with >320 living species of algae, invertebrates, and fish have been examined. The invasive mussel Mytilus galloprovincialis was present on >50% of those items. Size, reproduction, and growth of this filter-feeding species were examined to better understand long-distance rafting of a coastal species. The majority of mussels (79%) had developing or mature gametes, and growth rates averaged 0.075±0.018 SE mm/day. Structural and elemental (barium/calcium) analysis of mussel shells generated estimates of growth in coastal waters (mean=1.3 to 25mm total length), which provides an indication of residence times in waters along North America and the Hawaiian Islands prior to landing. Detailed studies of individual species contribute to our understanding of debris as a transport vector and aid efforts to evaluate potential risks associated with marine debris.