Genetic identification of macroalgal species on Japanese tsunami marine debris and genetic comparisons with their wild populations.

Since 2012 a huge amount of marine debris caused by the 2011 Great East Japan Earthquake and Tsunami has been arriving on Northeastern Pacific shores. Often healthy macroalgae were attached to them, which may become introduced to the Northwestern Pacific coasts and disturb their ecosystems. In order to elucidate the diversity of those macroalgae, and to establish a basis for detecting their new introduction to Northwestern Pacific coasts, we have examined their species diversity by morphology and genetic identifications. We have obtained gene sequences for 205 specimens, and identified 49 species as Japanese Tsunami Marine Debris (JTMD) macroalgae. Most of them are known to be distributed in Japan and showed identical or very closely related genetic types to those of Tohoku, and confirmed to be originated from the area. Several species such as Ceramium sungminbooi, Ectocarpus crouaniorum, Polysiphonia koreana, etc. have not been reported from Japan, but this is explained by the shortage of taxonomic information.