CHANGES IN SEA-ICE PHAGOTROPHIC MICROPROTISTS (20-200 MU-M) DURING THE SPRING ALGAL BLOOM, CANADIAN ARCTIC ARCHIPELAGO

Heterotrophic microflagellates and ciliates (i.e., 20-200 mu m size fr action) were examined for evidence of their response to the spring acc umulation of algal biomass in the bottom of the annual sea ice in Reso lute Passage (Canadian High Arctic, similar to 74 degrees N, 95 degree s W). The most abundant heterotrophic microflagellates were dinoflagel lates in the water column and cryothecomonad-type cells in the ice. Ci liates were exclusively represented by typical planktonic species in t he water column while the ice community was characterized by the occur rence of benthic-type species. This contrasts with observations in the Antarctic and at the southern limit of sea ice in the northern hemisp here, where annual sea ice seems to serve as a temporary habitat for p lanktonic communities. Protist biomasses in Resolute Passage were one to two orders of magnitude higher in the ice than in the plankton. In the ice, a seasonal increase in the biomass of phagotrophic microproti sts as well as in the number of micrometazoa (from our microprotist sa mples) followed the spring algal bloom. These observations (1) support previous suggestions of the existence of a functional microbial food web within sea-ice communities and (2) indicate that micrograzers may represent one of the basic levels of the ice food web that responds to the seasonal accumulation of algal biomass. Heterotrophic microprotis ts growing in the ice accumulated about 4 mg C m(-2) d(-1), a net prod uction rate that is two to four times higher than those reported for s ea-ice bacteria (both Arctic and Antarctic), and represented 1-9% of t he net production of ice algea in the early season at resolute. A carb on budget exercise indicated that the required energy for microprotozo an growth in the later season, when algal biomass was declining, corre sponded to 1-8% of the net biomass loss from the ice algal populations . The specific growth rates of microprotozoan populations within the i ce (0.04-0.18 d(-1)) appeared to increase significantly with decreasin g algal productivity. This may be critical for the protracted heterotr ophic food web in multi-year ice and to many consumers during the long polar winter.