| Summary: | IPY2012 Conference Montréal. From Knowledge to Action, 22-27 April 2012, Montréal, Canada Polar waters during winter are still one of the least known ecosystems in the world due to remoteness and harsh conditions. Yet, winter ecology is the necessary previous step for everything that occurs during spring and summer. The Canadian IPY project Circumpolar Flaw Lead Polynya Study (on board of the CCGS Amundsen) included a time series from the darkest (December 2007) to the most lit times of the year (June 2008) in Amundsen Gulf, a dynamic area due to the presence of a polynya. Our objective was to determine the activities and trophic relationships of planktonic microorganisms during winter. We observed that chlorophyll a decreased during the fall and early winter as expected. In middle February, however, chlorophyll started to increase exponentially despite the low light levels. This could be attributed to small flagellates, particularly Micromonas. This growth was followed by an increase in large flagellates that likely fed on these algae. Heterotrophic bacteria increased in numbers about a month later than the algal bloom and bacterivory by small pico and nanoflagellates followed. Thus, the first link of the trophic chain to become active after the total darkness period was autotrophic picoflagellates (mostly Micromonas) to large nanoflagellates. As a first approach to determine the role of this picophytoplankton we carried out several grazing experiments starting in winter (January 2008). We did 96-hour incubations with the in situ predator-prey community and an external alive Micromonas culture (RCC497 strain) as a tracer. The fascinating thing was that the grazing rates on Micromonas obtained were of the same order of magnitude as the in situ net death rates of the algae during December and January. This suggests that the decrease in chlorophyll a was not due to lack of light but to grazing. That is, the algae were able to subsist for a few months despite the absence of light. This is of larger significance, ...
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