Diversity, abundance and fate of ice algae and phytoplankton in the Bering Sea

Abstract

Sea ice algae are an essential part of Arctic and subarctic ecosystems. They significantly contribute to total algal primary production, serve as an early spring food source for both pelagic and benthic biota, and can seed the spring phytoplankton bloom during periods of ice melt. In the subarctic Bering Sea, virtually nothing has been known about the composition of the ice algal community, its magnitude, and its connection to pelagic and benthic ecosystems. This study, therefore, focused on the diversity, abundance, and ultimate fate of ice algae in the Bering Sea using sea ice, water and sub-ice sediment trap samples collected during two spring periods: ice growth (March to mid-April) and ice melt (mid-April to May) in 2008 and 2009. Ice algal species composition was comparable to those in Arctic regions. The phytoplankton species inventory was similar to that found in the overlying ice, suggesting that the spring phytoplankton were seeded from the ice algae. Algal abundance in the ice was on average three orders of magnitude higher than in the water column throughout both periods, as the extensive Bering Sea ice cover in 2008-2009 delayed the phytoplankton bloom. There was a substantial increase in the vertical flux of algal cells beneath the ice during the period of ice melt, but measurable amounts appeared as early as mid-March. The majority of this flux was composed of healthy algal cells, making it a rich food source for benthic organisms. Differences in the relative species composition between ice and trap samples indicate that algal fate was influenced by the species specific sinking rate of algal cells, among other factors, in the water column. In conclusion, ice algae in the Bering Sea are diverse and abundant, and contribute to both pelagic and benthic systems.