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The effect of stratification of microplankton communities in the northern Strait of Georgia Haigh, Rowan


The northern Strait of Georgia (NSG) and adjacent Malaspina Complex of inlets (MC) were studied to determine the effect of stratification on microplankton communities. The NSG was dominated by nanoflagellates in spring. There was no evidence of a vernal diatom bloom in the Strait, perhaps due to wind turbulence or microzooplankton grazing. In early summer regimes were conducive to diatom growth but the northern Strait was experiencing a "mild" red tide. By late summer, diatoms bloomed and prevailed, presumably, till the fall decline. Stratification was greatest in late summer, due chiefly to temperature, with reduced surface salinities on the east side from Fraser River runoff. At this time biological partitioning was pronounced, resulting in a mosaic of organismal groups. Although stratification had declined by early autumn, the mosaicism was maintained and strengthened. Diatoms were most abundant in the north and on the west side where stratification was least, in areas of tidal turbulence. Photosynthetic nanoflagellates and photosynthetic dinoflagellates favoured the more stratified east side. Ciliate distributions mirrored those of the nanoflagellates. The MC was thought to be a more stratified version of the NSG but it was found to be a fairly mixed water body due to tidal action. It was sheltered from winds which allowed the early blooming of diatoms. These were maintained for several months by a tidal jet through Malaspina Inlet that probably injected nutrients into the junction of Malaspina, Okeover, and Lancelot Inlets. Principal components analysis was used to reduce the dimensionality of the biological dataset, and canonical correlation analysis allowed the coupling of environmental data to the biological principal components. It was found that PCI reflected general biomass while PC's II and III were most often related to depth and location. These latter two were utilised to resolve the species information in three-dimensions. In general, nanoflagellates populated surface waters whereas diatoms tended to occupy deeper depths. Multiple regression analysis was performed on organismal groups to explore how biomass was affected by stratification, pycnocline depth, surface temperature (seasonality), nitrate, and grazing.

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