Mesopelagic protists: Diversity and succession in a coastal Arctic ecosystem

Abstract

We investigated marine protist diversity from below the euphotic zone during 4 consecutive seasons(November 2003 to July 2004) from a fixed station in the Canadian Arctic(Franklin Bay, Beaufort Sea). DGGE analysis and 18S rRNA gene clone libraries showed that this mesopelagic protist community was dynamic, with marked changes in taxonomic and functional community composition in different seasons. The most frequently recovered sequences in autumn were related to heterotrophic dinoflagellates. In late December 2003, an abrupt change in the community composition occurred following aninflu×of water from the lower Pacific halocline that flowed onto the Arctic continental shelf and into Franklin Bay. Subsequently, the most frequently retrieved sequences matched uncultured marine alveolates, which are thought to be primarily parasites. This community changed little over the winter, with modest changes in spring marked by the addition of taxa. Summer libraries from 2004 were once more dominated by dinoflagellate sequences with a community very similar to that at the end of autumn 2003. These summer and autumn communities corresponded to periods of higher phytoplankton sedimentation rates in the euphotic zone. We suggest that the deep protist community may reform annually in response to primary production higher in the water column and that the winter mesopelagic protist community is dynamically coupled to the deep off shore ocean. © Inter-Research 2009.