Protist biodiversity and Microbial Food Webs in the North Water Polynya:

The relationships between protist species composition, community structure, water column characteristics and nutrients were investigated in the North Water Polynya (NOW), a recurring area of open water surrounded by sea ice in the eastern Canadian Arctic. Unlike other regions in the Arctic, large phytoplankton and other protists (cell diameter >20 micrometers) dominated over 4 months of sampling (April-July 1998). A ternary community distance index was developed and used to quantify the variability in protist community structure in the hydrographically heterogeneous upper water column of the NOW. This index was highly correlated (r = 0.984, n = 6) with the extent of physical interleaving, quantified as the RMS deviations in temperature between measured and smoothed profiles. This relationship indicated a high degree of physical biological coupling within the water column. Bacterial and viral concentrations were greater in regions with more layers and significantly higher concentrations of open membrane bacteria, visualized using a novel staining technique, were also found in more interleaved water columns.

Interleaving waters were a result of the advective input of nutrient rich Arctic Ocean waters into waters formed in Northern Baffin Bay. Shipboard microcosms (small scale container incubations) were used to experimentally test whether specific protist communities could be selected for under advective versus non advective conditions. An advective treatment, based on semi-continuous cultures, was compared to a treatment where nutrients were recycled. The bloom species and high production were maintained in the advective treatment. In both the advective treatment and the recycled nutrient treatment there was continued production by ciliates and large naked heterotrophic dinoflagellates. Thalassiosira spp. and Chaetoceros spp. that were dominant in the advective treatment were also dominants over northern and western regions of NOW in June 1998, at time when there was active advective interleaving. The large (40-80 mm) heterotrophic gymnodinoid dinoflagellates that were dominant in the recycled treatment were recorded throughout NOW in June and July and were dominants over the eastern portion of NOW, where interleaving was weak or absent. The persistence of interleaving and continued advective nutrient input may explain the high productivity and biodiversity (270 protist taxa) of the NOW polynya