Sea-ice microbial communities in the Ross Sea: Autumn and summer biota

Abstract

The composition of sea ice communities in the Ross Sea region was examined during the autumn to winter transition and during the summer. The biomass of autotrophs and heterotrophs in autumn reached maximum values of 709 and 167 mg C m-2, and in summer maximum values of 3873 and 209 mg C m -2, respectively. During the autumn-winter cruise, most of the biomass was found within ice floes as interior and bottom layer communities. During summer, surface-layer slush communities occurred throughout the ice-covered regions. The biomass was highly variable throughout the study regions during both cruises. Diatoms dominated the autotrophic biomass; however, autotrophic dinoflagellates and autotrophic flagellates contributed significantly to the community make-up. Among heterotrophs, cillates predominated during both cruises, followed by heterotrophic flagellates and heterotrophic dinoflagellates. Similarity analysis, based on the biomass composition of major groups, showed consistency between and within cruises, with most samples >70% similar. The autumn to winter samples (all from within floes) showed higher similarity clusters that could be related to changing compositions of diatoms, ciliates, and autotrophic dinoflagellates. Most variable were some summer surface slush samples, where samples dominated by Phaeocystis, Pyramimonas, Gymnodinium, and the ciliate Gymnozoum formed outlying clusters. The dynamics of ice biota may be determined by relatively few taxa that are persistently found within the ice floes. Surface blooms may develop either from a biota within the ice or from opportunistic forms from the water column that are introduced during flooding events. Thus, these assemblages may show considerably more variability in composition than those that develop within the underlying ice. © Inter-Research 2005.