Comparison of bottom-up processes in Canadian subregions of the Salish Sea

The Salish Sea is a complex coastal region wherein annual variations in prey availability for salmon have changed over time. Specific areas within this region have distinct physical oceanographic features and thus may play an important role in seasonal and interannual variability of lower trophic levels. As part of the Salish Sea Marine Survival Project we are investigating how bottom-up processes differ between regions within the Canadian areas of the Salish Sea, in part to determine if variations in prey availability in these subregions affect the health and/or foraging success of young herring and salmon. Environmental drivers (SST, PAR, wind), oceanographic conditions (from CTD data), in addition to phytoplankton and zooplankton community composition will be compared across the different subregions. Hotspot analyses on mean monthly phytoplankton and zooplankton biomass will provide information as to which areas are more productive. In addition, a simultaneous data-driven approach based on taxonomic composition will indicate how well our defined subregions represent natural spatial distributions of phytoplankton and zooplankton communities. Preliminary results of satellite-derived chlorophyll a from 2015 show that the Juan de Fuca and Tidal Mixed regions had consistently lower phytoplankton biomass throughout all seasons. Analysis of in situ phytoplankton samples revealed similar results with relatively low cell densities occurring in the Tidal Mixed region throughout the year. In contrast, the Central region had the highest phytoplankton biomass in the spring, whereas the highest biomass in the summer was observed in the Northern region. Variations were also observed in monthly anomalies of zooplankton biomass, with the highest positive anomalies occurring in Baynes Sound. Results from this work will ultimately be combined with juvenile salmon studies to address whether variations in prey availability within these different subregions affect the health and survival of juvenile salmon in the northern Salish Sea