Abstract:

Abundance, biomass and composition of the ice algal and phytoplankton communities were investigated in the southeastern Laptev Sea in spring 1999. Diatoms dominated the algal communities and pennate diatoms dominated the dia- tom population. 12 dominant algal species occurred within sea ice and underlying water column, including Fragilariopsis oceanica, F.cylindrus, Nitzschia frigida, N. promare, Achnanthes taeniata, Nitzschia neofrigida, Navicula pelagica, N.vanhoef fenii, N.septentrionalis, Melosira arctica, Clindrotheca closterium and Pyrarnimonas sp. The algal abundance of bottom 10 cm sea ice varied between 14.6 and 1562.2×10⁴ ceils l^-1 with an average of 639.0×10⁴ cells l^-1, and the algal biomass ranged from 7.89 to 2093.5μg C l^-1 with an average of 886.9μg C l^-1, which were generally one order of magnitude higher than those of sub-bottom ice and two orders of magnitude higher than those of underlying surface water. The integrated algal abundance and biomass of lower most 20 cm ice column were averagely 7.7 and 12.2 times as those of upper 20 m water column,respectively,suggesting that the ice algae might play an important role in maintaining the coastal marine ecosystem before the thawing of sea ice. Ice algae influenced the phytoplankton community of the underlying water column. However, the “seeding” of ice algae for phytoplankton bloom was negligible because of the iow phytoplankton biomass within the underlying water column.

Key words: ice algae, phytoplankton, biomass, Laptev Sea, Arctic