CARBON FLOWS THROUGH THE MICROBIAL FOOD-WEB OF FIRST-YEAR ICE IN RESOLUTE-PASSAGE (CANADIAN HIGH ARCTIC)

Ice algal communities are host to thriving populations of microheterot rophs whose trophic role remains poorly understood. We report here an inverse modelling analysis of the microbial food web associated with t he spring bloom of ice algae at Resolute Passage in the High Arctic. C arbon flows among microbial components (ice algae, autotrophic and het erotrophic nanoflagellates, microflagellates and ciliates) and their e xchanges with particulate and dissolved organic carbon (POC and DOC) w ere inferred from the observed changes in standing stocks of these com partments between 13 April and 22 May 1992. Calculations were made for three phases of the bloom's development and for two sites under thin and thick snow cover. Observed DOC accumulations within the bottom ice originated largely from the ice algae. However, calculated production rates were too high to result strictly from normal physiological exud ation. Mechanical or physiological stresses that disrupt the integrity of the cells and grazing by zooplankton at the ice-water interface ma y well be involved in this process. Inverse modelling confirmed field and experimental evidence that nanoflagellates may directly assimilate DOC to support their growth. Patterns in trophic flows between sites with thin and thick snow cover were similar. In contrast, trophic inte ractions changed as the bloom progressed: production of DOC and detrit us from the ice algae were the only significant carbon flows during th e early phase; bacterivory developed and peaked during the middle phas e and was superseded by DOC utilization and herbivory by flagellates a nd ciliates during the late phase. Only ca. 20% of the DOC produced wa s utilized by the microheterotrophs. Direct links from DOC and ice alg ae to protists potentially increase the efficiency of C transfers with in the ice-associated microbial food web; on the ether hand, low recov ery efficiency limits the role of the microbial loop in recycling DOC.