Biomass and species composition of microalgae (ice algae) in drifting sea-ice collected in coastal waters off Mombetsu, Hokkaido, in the Okhotsk Sea

Abstract

Microalgal assemblages were collected from drifting sea-ice and sea-surface waters in the coastal waters off Mombetsu, Hokkaido, in the Okhotsk Sea during the winter of 2011 and 2012, and the biomass and species composition of the assemblages were examined. Chlorophyll a concentration and cell density in the colored parts of the drifting sea-ice varied in the range of 24.1–104.0 mg m^-3 and 5.10–15.38×10⁶ cells L^-1, respectively. Based on cell density, the dominant taxa were the pennate diatoms Achnanthes taeniata and Fragilariopsis spp., the centric diatoms Thalassiosira spp. and Chaetoceros socialis. Pennate diatoms commonly dominated in the microalgal assemblages from sea-ice samples. On the other hand, Thalassiosira spp. was the most dominant taxon in all sea-ice samples based on carbon biomass. From the results of the present and previous studies, it is suggested that Thalassiosira spp. play an important role in the ice-edge and spring phytoplankton blooms.