Nitrate uptake by size-fractionated phytoplankton on the Scotian Shelf (Northwest Atlantic): spatial and temporal variability

New (nitrate) phytoplankton production was estimated monthlyduring 1 year (March 1991–March 1992) at three stationson the Scotian Shelf, Northwest Atlantic. Samples were sizefractionated to assess the uptake of nitrate by small (<5µm) and large (>5 µm) phytoplankton. The biomassof small phytoplankton remained relatively constant over theyear, whereas that of the large size fraction was high in earlyspring and low during the remainder of the year. Monthly variationsin nitrate uptake were similar for the two size fractions, suggestingthat both small and large phytoplankton used nitrate when available.It follows that, outside the spring bloom, new production waslargely due to the small fraction. Our results do not supportthe notion that new production is associated with large phytoplanktonand regenerated production with small phytoplankton.