Nutrient and phytoplankton dynamics in the Queen Charlotte Islands (Canada) during the summer upwelling seasons of 2001-2002

The Queen Charlotte Islands, Canada, lie at the northern extreme of the coastal upwelling system of the eastern North Pacific Ocean (51-54°N). In this study, the first observations of spatial and inter-annual patterns in nutrient inventories, chlorophyll (Chl) a and phytoplankton assemblages are reported and related to oceanographic conditions in near-shore waters of the island archipelago. Stronger and more persistent upwelling in 2002 coincided with higher nutrient and Chl a standing stocks compared to 2001 and a higher proportion of diatoms. Dinoflagellates were more prevalent in 2001, including several potentially harmful species. At sub-seasonal scales, Chl a concentrations were greatest during downwelling conditions and smallest during upwelling conditions. On the west coast, weak water column stratification, high relative proportions of diatoms and large nutrient inventories accompanied upwelling-favourable conditions, whereas on the east coast, there was no direct relationship between the Bakun Upwelling Index and water column stability. According to redundancy analysis, variability in species composition was best explained by sea surface temperature, the depth of the euphotic zone and nutrient inventories. The east coast supported blooms of coccolithophores within protected bays, confirming previous satellite observations that showed bright patches in these areas. The data illustrate that moderate upwelling can have an important influence on near-shore algal standing stocks and species composition at the northern extreme of the upwelling system off the west coast of North America, and that topographical complexity may be important for the development of phytoplankton blooms.