Genetic structure of Japanese sea cucumbers (Apostichopus japonicus) along the Sanriku coast supports the effect of earthquakes and related tsunamis.

The Japanese common sea cucumber (Apostichopus japonicus) is a major marine product from Sanriku, Japan, but its populations were severely affected by the 2011 Tohoku earthquake, possibly decreasing its genetic diversity and increasing its extinction risk. In this study, we estimated the genetic structure and diversity of sea cucumbers from Touni and Yamada Bays of Sanriku over 4 years after the earthquake. The between-population genetic structure was estimated using two mitochondrial DNA regions (cytochrome c oxidase subunit I and 16S rDNA). Genetic differentiation (as measured by pairwise FST) was not significant between locations. Thus, even after the tsunami, gene flow and genetic diversity among the two sea cucumber populations were maintained. Our data also suggested that sea cucumbers in Sanriku experienced population expansion of about 0.20-0.24 million years ago, during the stable Mindel-Riss interglacial period. We conclude that A. japonicus populations in Sanriku could maintain their genetic structure throughout multiple disastrous tsunamis over the past several 1000 years. The high dispersal ability of planktonic larvae may enable the entrance of new recruits, thereby reducing risks associated with genetic structure and diversity changes stemming from mass die-offs in a given body of water from the past to the present.