Since the early 1970s, many artificial reefs (ARs) have been deployed in Japanese coastal waters to create fisheries grounds. Recently, researchers began to use environmental DNA (eDNA) methods for biodiversity monitoring of aquatic species. A metabarcoding approach using internal standard DNAs [i.e., quantitative MiSeq sequencing (qMiSeq)] makes it possible to monitor eDNA concentrations of multiple species simultaneously. This method can improve the efficiency of monitoring AR effects on fishes. Our study investigated distributions of marine fishes at ARs and surrounding stations in the open oceanographic environment of Tateyama Bay, central Japan, using qMiSeq and echo sounder survey. Using the qMiSeq with 12S primers, we found higher quantities of fish eDNAs at the ARs than at surrounding stations and different fish species compositions between them. Comparisons with echo sounder survey also showed positive correlations between fish eDNA concentration and echo intensity, which indicated a highly localized signal of eDNA at each sampling station. These results suggest that qMiSeq is a promising technique to complement conventional methods to monitor distributions of multiple fish species.

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The present situation of utilization and the eŠects of artiˆcial reefs on the resource density of Japanese butterˆsh Hyperoglyphe japonica and red seabream Pagrus major in the waters of the Iki Islands

The impact of the great tsunami, which was generated by the Great East Japan Earthquake on 11 March 2011, on the quality of a nursery ground for juvenile Japanese flounder Paralichthys olivaceus with a sandy bottom of <15 m in depth in Sendai Bay, Japan, was evaluated. Growth rates of juveniles, as an index of the quality of the nursery ground, were compared between before and after the tsunami. Recent growth rates (RGR; mm day−1) between 1 and 6 days before collection in 2011–2013, which were estimated from the width of otolith increments, ranged from 0.84 to 2.37 mm day−1 for juveniles of 24.8–146 mm in total length (TL). These figures are comparable to the maximum RGR for juvenile Japanese flounder in the literature. A linear model for RGR selected TL and bottom temperature but rejected biomass of the mysid Orientomysis mitsukurii, the main prey item, as explanatory variables, indicating that the growth rates of juveniles after the tsunami were not controlled by food density, i.e., optimal food condition occurred in the nursery. A linear model for observed growth rate (mm day−1), which was calculated from the temporal changes in the juvenile size frequency distribution, suggested the growth rate did not change between before and after the tsunami. Additional information on prey abundance and sediment size distribution also support this conclusion. Therefore, we conclude that the quality of the nursery ground for juvenile Japanese flounder in the study site has not been damaged by the great tsunami.