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The purpose of the present paper was to examine the genetic population structure of Buccinum tsubai in the Japan Sea. Mitochondrial 16SrRNA gene sequence analysis was performed with specimens from various stations in the Japan Sea. Mitochondrial lineages were clearly patterned geographically in four separate areas: the Hokkaido area, the Yamagata–Toyama area, the Yamato Bank area, and the San’in area. The main distribution depth range of B. tsubai is between 200 m and 1000 m isodepths, and the horizontal distance between the 200 m and 1000 m isodepth lines represents the specific spatial scale of the habitat (SSSH). These four areas were separated either by the complete discontinuity of the SSSH area or by its narrow spatial extension. Genetic distances between the main haplotypes of each area were calculated as Jukes–Cantor distances, the value of which ranged between 0.012 and 0.017. This value seemed to be unrelated to the geographic distance. There was no tendency for clustering according to depth. In future, the morphological characters of the four lineages of B. tsubai should be compared in detail in order to elucidate significant genetic differences among them. [ABSTRACT FROM AUTHOR]

The diversity of cyanobacteria and diazotrophs in the Japan Sea was investigated by analyzing sequences of cyanobacterial 16S rRNA genes and nitrogen fixation genes ( nifH) from seawater sampled at depths ranging from the surface to 100 m at two stations. Of the 107 cyanobacterial 16S rRNA gene sequences obtained, 97 and three sequences were assigned to Synechococcus sub-cluster 5.1 and Prochlorococcus HL (II), respectively. Unlike other oceanic regions, at our two sampling stations the composition ratio of the sequences assignable to Synechococcus sub-cluster 5.3 was relatively high (8 %). No sequences of diazotrophic cyanobacteria were found in the cyanobacterial 16S rRNA genes. In the nifH clone library (36 sequences), ten sequences were identified as a UCYN-A group of diazotrophic cyanobacteria; the other 26 sequences (72 %) were assigned to proteobacteria. These results suggest that heterotrophic bacteria, including UCYN-A, dominate the diazotrophic community in the Japan Sea. Our study reveals the dominance of Synechococcus in cyanobacterial community and (photo)heterotrophic diazotrophs in the diazotrophic community in the Japan Sea, suggesting its unique characteristics. [ABSTRACT FROM AUTHOR]

SUMMARY:The productive structure and productivity of a Sargassum macrocarpum C. Agardh population were studied from June 1993 to July 1994 in Fukawa Bay facing the Sea of Japan, Yamaguchi Prefecture. S. macrocarpum formed a dense population at a depth of 8 m in the study area. Using the stratified clip technique, monthly changes in the productive structure from 1993 to 1994 were clarified. The dry weight of leaves and main branches increased with the elongation of branches. Thalli in the middle to high stratum began to bear receptacles from March 1994 and the dry weight of receptacles was approximately one-third of the standing crop in June. The loss of leaves increased from April to June 1994, and the loss of main branches and receptacles from June to July 1994. Productivity of branches and receptacles reached maxima of 4.67 g dry wt/m2 per day from February to March and 5.33 g dry wt/m2 per day from April to May, respectively. Productivity of the leaves, however, was almost constant at approximately 2 g dry wt/m2 per day from July 1993 to March 1994. Therefore, maximum productivity of the S. macrocarpum population of 7.17 g dry wt/m2 per day occurred from February to March. Annual net production of newly sprouting branches in June 1993 was 1600.1 g dry wt/m2 per year based on the summation method, which was calculated from the monthly changes in the productive structure. [ABSTRACT FROM AUTHOR]