Species composition of Skeletonema (Bacillariophyceae) in planktonic and resting-stage cells in Osaka and Tokyo Bays

Abstract

Species compositions of planktonic cells and benthic resting-stage cells of the marine diatom Skeleto- nema were investigated in Osaka and Tokyo Bays. Seven to 11 strains were isolated from each of the monthly water samples for species identification by molecular analysis. The species frequency of the strains indicated that S. sp. cf. marinoi-dohrnii complex was dominant throughout the year in Osaka Bay, whereas in Tokyo Bay the dominant spe- cies was replaced by S. japonicum during the cold season. The other species identified were S. costatum, S. japonicum, S. pseudocostatum, and S. tropicum in Osaka Bay, and S. menzelii and S. tropicum in Tokyo Bay. For species identifi- cation of resting-stage cells, sediments in each bay were sampled at 2-3 stations and stored in the dark for ≥85 days. Eight to 12 strains were isolated from each of the diluted sediments incubated at five temperatures (10-30°C). S. costatum, S. japonicum and S. sp. cf. marinoi-dohrnii complex were identified in these stains; the resting stage of S. japonicum was newly recognized. The dominant species of resting-stage cells in each bay largely agreed with those of planktonic cells on a yearly basis. S. sp. cf. marinoi-dohrnii complex in the sediment could germinate at all the temperatures but S. japonicum did not occur at 30°C. The results of seasonal occurrences and incubation experi- ments indicate that S. sp. cf. marinoi-dohrnii complex is eurythermal and S. japonicum prefers lower temperatures. Possible factors for the difference in the community of Skeletonema between Osaka and Tokyo Bays are discussed.