Late-summer distribution of phytoplankton in relation to water mass characteristics in Hudson Bay and Hudson Strait (Canada)

Abstract

Descriptive and multivariate analytical methods were used to analyze the early September (1993) abundance and species composition of phytoplankton in relation to water mass characteristics in Hudson Bay and Hudson Strait. Four groups of stations distributed along well-defined environmental gradients characterizing the distribution of physical and chemical variables were identified. The first group, located in the most southern region of Hudson Bay, was strongly influenced by freshwater runoffs from James Bay and from the other major rivers around the bay and was characterized by a relatively high phytoplankton biomass (chlorophyll a (Chl a) > 1.0 µg ·L-1) in the near-surface waters and by a phytoplankton assemblage equally dominated by small flagellates and dinoflagellates. The second group, located in an area northwest of the Belcher and Sleeper islands, was characterized by relatively well-mixed conditions where small diatoms composed about 50% of the phytoplankton assemblage. The third group occupied the upper part of the bay and the entrance of the strait and was characterized by the lowest surface nutrient concentrations encountered. A clear subsurface chlorophyll maximum dominated by small flagellates (>55% of the assemblage) was observed in this region. The fourth group was located in the central part of the strait where the highest surface nutrient concentrations and phytoplankton biomass values (Chl a > 2.0 µg ·L-1) were observed. The phytoplankton assemblage there was clearly dominated by small diatoms (>80%). These conditions are related to the presence of more intense tidal mixing in this region. The phytoplankton standing crop within this area was comparable with that observed during an autumn bloom situation in most temperate regions of the world's ocean.