Distribution of viable resting stage cells of diatoms in sediments and water columns of the Chukchi Sea, Arctic Ocean

Abstract:

The distribution of resting stage cells of diatoms in the surface sediments and water samples collected in the Chukchi Sea was investigated using the most probable number (MPN) analysis to understand the mechanism underlying diatom blooms in the Arctic region. High densities (3.5 × 10⁵ to 6.8 × 10⁶ MPN cells cm⁻³ wet sediment) of viable resting stage cells of typical Arctic diatom species were found in the surface sediments of the Chukchi Sea. Resting stage cells of the sea-ice–related diatom genus Fragilariopsis were more abundant (2.6 × 10⁶ MPN cells cm⁻³ wet sediment) than Chaetoceros (2.18 × 10⁶ MPN cells cm⁻³ wet sediment) or Thalassiosira (1.76 × 10⁶ MPN cells cm⁻³ wet sediment) in the southern Chukchi Sea. This reflected a previous bloom of Fragilariopsis ahead of typical planktonic blooms of Chaetoceros and Thalassiosira and suggests that sea-ice–related blooms are a substantial factor for primary production in this area. During the sampling period, diatom assemblages in the in situ water columns were dominated by Pseudo-nitzschia delicatissima, Cylindrotheca closterium, Proboscia alata, and Thalassionema spp. After storage of water samples for 6 months in the dark, viable diatom resting stage cells of typical Arctic species such as Attheya longicornis and Chaetoceros socialis were detected. These autochthonous species formed resting stage cells that remained viable in the dark for more than 6 months, while diatom species of Pacific origins could not survive under conditions of extremely limited light. The resting stage cells provide an advantage for autochthonous diatoms to endure the unfavourable light conditions of the Arctic winter. In the Chukchi Sea, resting stage cells of diatoms were supplied by current inflows from shallow sea areas. Densely distributed viable resting stages at the bottom are also a possible source for seeding the diatom cells into phytoplankton communities and ice assemblages in shallow marginal ice zones.

Key Words::

• Chukchi Sea
• Diatom
• Ice algae
• Phytoplankton bloom
• Resting stage cells

ACKNOWLEDGEMENTS

We thank the captains and crew of R/V Mirai for their help in sampling and for supplying the environmental data. Professor Kenshi Kuma (Graduate School of Fisheries Sciences, Hokkaido University) provided valuable comments on an earlier draft of the study.