ANTARCTIC SEA ICE BIOTA

The sea ice surrounding Antarctica provides an extensive habitat for organisms ranging in size from bacteria to marine birds and mammals. Historically, most of the ecological work on the ice biota has focused in the nearshore land-fast ice. Only in the last decade have there been comparable studies in the deep-water pack ice regions. These studies have indicated that there are fundamental differences in structural and physical characteristics of fast and pack ice that are a result of differing physical regimes in near-shore and oceanic regions. Other physical processes act to create heterogeneity within the ice habitat that can range from geographic and regional scales of patchiness to a pronounced vertical gradient within ice floes. The conspicuous patterns in the distribution of the ice biota can be explained largely by these physical processes. Over 200 species have been reported living on, in, or in association with Antarctic sea ice. The ice biota includes bacteria, a variety of algae, heterotrophic protozoans and small metazoans. The diatom assemblages are the only taxonomic group that is known well enough to make comparisons among the various habitats. Studies by a number of workers suggest some specific diatom assemblages along with occurrence of species that are widely-distributed in both ice and plankton. Ice may also serve as a temporary habitat for species that also comprise planktonic communities, so that providing a "seed population" for ice edge plankton blooms may be an important role of the ice biota. Trophic interactions among organisms in ice suggest that the ice assemblage is a true community with a well-developed microbial food web. The ice microbial community may be an important part of the Antarctic marine food web because large consumers from the adjacent planktonic and benthic communities appear to feed on the ice biota.