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Background: DNA barcoding is an effective method of accurately identifying morphologically similar oyster species. However, for some of Japan's Ostrea species there are no molecular data in the international DNA databases. Methods: We sequenced the mitochondrial large subunit ribosomal DNA (LSrDNA) and cytochrome c oxidase subunit I (COI) gene of five known and two unidentified Ostrea species. Phylogenetic comparison with known Ostrea species permitted accurate species identification by DNA barcoding. Results: The molecular data, which were deposited in an international DNA database, allowed for a clear distinction among native Ostrea species in Japan. Moreover, the nucleotide sequence data confirmed that O. stentina (Atsuhime-gaki) inhabits Kemi and Ibusuki, Japan. Conclusions: This is the first record of O. stentina in Japan. These results provided for accurate species identification by DNA barcoding of the taxonomically problematic species O. futamiensis, O. fluctigera, O. setoensis and O. stentina in Japan.

Densities of sandy beach organisms along coastlines often vary considerably even within small local scales. In order to understand the demographic basis of density variations in shore animals, we examined the population dynamics of the amphipod Haustorioides japonicus Kamihira, which is an ideal subject because it lacks a planktonic dispersal stage in its life history. Quantitative sampling at three adjacent sandy beaches along the Sea of Japan coast revealed that the spring density, i.e., the density of overwintered individuals, was similar among the three beaches. However, the amount of recruitment of newly hatched juveniles from late spring to summer greatly differed among the beaches, resulting in large spatial variations in the summer density. Cohort analyses revealed that at all beaches, young‐of‐the‐year (YOY) individuals reproduced and then died, and that individuals which recruited in late summer overwintered. Moreover, growth, fecundity, and survival schedules of overwintered and YOY individuals were very similar among beaches. These observations suggest that the difference in recruitment success, i.e., the survival of newly hatched juveniles, is the primary cause of the inter‐population variation in the summer density. It is likely that variations in salinity and sandy sediment affect the recruitment success of newly hatched individuals. This study indicates that biological productivity may differ substantially even among adjacent sandy beaches, with important implications for beach management.

Zonation has been a major focus of intertidal ecology. In general, sandy beaches are thought to have three zones (supralittoral, littoral, and sublittoral zones). In the present study, 41 areas of sandy beaches were surveyed along the Japan Sea coast of Honshu (from Aomori to Yamaguchi Prefectures) characterized by a small tidal range, large seasonal fluctuations in the mean tide level, and harsh wind-driven waves in winter, and the applicability of the three-zone scheme was examined. Overall, a total of 316 beach stations were surveyed, 28 taxonomic units were identified, and the most abundant species was the amphipod Haustorioides japonicus. The taxonomic units were grouped using multivariate techniques into a total of 7 assemblages, and the relationship of these assemblages to zonation was examined. Investigation of the indicator species of the 7 assemblages and their vertical position on the beaches showed that one assemblage corresponded to the supralittoral zone (indicators were talitrid amphipods and the isopod Tylos granuliferus). Another assemblage corresponded to the sublittoral zone, and the other five assemblages to the littoral zone. The assemblage of the sublittoral zone tended to disappear on the northern beaches, while one of the littoral assemblages whose indicators included a mysid species, Archaeomysis kokuboi, tended to occur on the northern beaches. Thus, the three-zone scheme can be applied to sandy beaches of the Japan Sea, but there are large variations among the beaches.