Evaluation of the tsunami impact on the genetic diversity of the marbled flounder Pseudopleuronectes yokohamae in Sendai Bay, Miyagi, Japan

Evaluating genetic diversity is a fundamental step for stock management. However, it can be influenced by environmental and demographic changes, and thus it should be carefully investigated, especially when drastic disturbances have occurred. Marbled flounder Pseudopleuronectes yokohamae is a commercially valued fish in Japan, and possibly consists of multiple management units due to its benthic lifestyle including low dispersal ability. In Sendai Bay (Japan), the population is thought to form a single management unit, and its spawning ground has been protected for stock conservation. Since this population could have been strongly affected by the huge tsunami associated with the 2011 off the Pacific coast of Tohoku Earthquake, the tsunami impact on the genetic diversity of the population of the marbled flounder in Sendai Bay needs to be evaluated. We firstly developed genomic resources for this species using next generation sequencing technology and de novo assembly, which generated a total of 525,502 contigs and 10,732,070 unassembled reads. We then designed a total of 331,368 microsatellite primer pairs from the genomic data, and characterized sixteen primer pairs as novel microsatellite loci. Using these microsatellite markers, significant genetic divergence was found between the east and west sides of Boso Peninsula (pairwise FST = 0.02305 - 0.19784). At the east side, genetic homogeneity was observed over the wide area from Onagawa Bay to Choshi including Sendai Bay, except for Mutsu Bay. The genetic variability of the Sendai Bay population did not show any considerable changes after the tsunami from April 2012 to February 2014 (HE = 0.5061 - 0.5463) and was relatively higher compared to those of the western populations of Boso Peninsula (HE = 0.3817 - 0.4557). These results suggest that the tsunami impact on the Sendai Bay population of the marbled flounder is considered to be minor but long-term monitoring may be needed.