Seasonal dynamics of oceanographic conditions, phytoplankton, and zooplankton in the Malaspina Strait, Strait of Georgia

Plankton dynamics in the Salish Sea may directly impact resident and migratory fish populations that are of major economic importance in the region. The Malaspina Strait in the northern Salish Sea is of particular interest as it is an important migration route for juvenile salmon. Here, we present data collected at three stations in the Malaspina Strait as part of the Citizen Science initiative of the Salish Sea Marine Survival Project. Sampling was conducted at bi-monthly (or higher) frequency from February to October, 2015 to 2017. Relationships between the regional hydrography, environmental parameters (temperature, salinity, dissolved oxygen, etc.), nutrient concentrations, and phytoplankton and zooplankton community composition are considered. Preliminary results indicate that 2015 was an anomalous year with an earlier-than-average (mid-February) spring phytoplankton bloom. Phytoplankton community composition was dominated by centric, chain-forming diatoms in spring of all years, cell densities were higher in spring 2015 compared to 2016 and 2017. In both 2015 and 2016, copepods dominated the abundances of zooplankton at the deep locations in Malaspina Strait. However, the biomass was dominated by taxa known to be the preferred prey of juvenile salmonids (euphausiids, amphipods, crab larvae). At the nearshore station in both years, zooplankton biomass was dominated by “other” taxa, in particular gelatinous plankton. Biomass of large calanoid copepods and euphausiids was significantly positively correlated to the relative abundance of diatoms. Biomass of small calanoid copepods and non-calanoid copepods, on the other hand, was positively correlated with the relative abundance of dinoflagellates. Further analyses will relate environmental variables to the observed seasonal variations in phytoplankton and zooplankton. Results from this study will ultimately be extended to include other Citizen Science stations in order to gain a better understanding of how bottom-up processes vary in different regions of the Salish Sea, and the potential implications for higher trophic levels

Influence of environmental drivers on satellite-derived chlorophyll a in the Strait of Georgia from 2003-2016

The Salish Sea is a dynamic region with substantial temporal and spatial variability at lower trophic levels. This variability, in turn, may directly impact resident and migratory fish populations that are of major economic importance. Here, we examine the relationships between environmental drivers (e.g. SST, wind, river input) and patterns of satellite-derived chlorophyll a (chl a) from 2003-2016 in the Northern and Central Strait of Georgia. Average spring bloom start date in the Salish Sea occured in late March. Strong positive chl a anomalies in spring 2005 and 2015 resulted in the early spring blooms (mid-February). Anomalously high chl a concentrations ([greater than] 20 mg m-3) were also observed in autumn 2008 in the Central region, which was twice as high as the maximum values typically observed in autumn throughout our time series. In contrast, later than average (late April) spring blooms occurred in 2007 and 2008. Results from analysis of the environmental drivers showed positive SST anomalies predominated between 2003-2006 and 2013-2016, with the highest anomalies occurring in spring 2015. Strong positive anomalies in Fraser River discharge, coupled with strong negative wind anomalies, occurred in both spring 2005 and 2015. Chl a in the Northern region was most highly correlated with SST and PAR (r = 0.328, p\u3c0.0001 and r = 0.347, p\u3c0.0001, respectively), whereas chlorophyll a in the Central region was most highly correlated with Fraser River discharge (r = 0.264, p[greater than]0.0001). Similar analyses on anomaly data revealed that chl a anomalies in both the Northern and Central regions were highly correlated with SST and PAR anomalies. Ultimately, results from this study will be paired with zooplankton data to provide insight into how changes in the seasonal patterns of lower trophic levels may influence the growth, survival, and overall return strength of salmon populations in the region

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

The Canadian Beaufort Shelf trophic structure: evaluating an ecosystem modelling approach by comparison with observed stable isotopic structure

Climate-driven impacts on marine trophic pathways worldwide are compounded by sea-ice loss at northern latitudes. For the Arctic, current information describing food web linkages is fragmented, and there is a need for tools that can describe overarching trophic structure despite limited species-specific data. Here, we tested the ability of a mass-balanced ecosystem model (Ecopath with Ecosim, EwE) to reconstruct the trophic hierarchy of 31 groups, from primary producers to polar bears, in the Canadian Beaufort Sea continental shelf. Trophic level (TL) estimates from EwE were compared with those derived from two nitrogen stable isotope (SI) modelling approaches (SI linear and scaled) to assess EwE accuracy, using a dataset of 642 δ15N observations across 282 taxa. TLs from EwE were strongly, positively related to those from both SI models (R2 > 0.80). EwE performed well (within 0.2 TL) for groups with relatively well-known diets or for taxa characterized by fewer trophic connections (e.g., primary consumers). Performance was worse (> 0.5 TL) for species groups aggregated at coarse taxonomic levels, those with poorly documented diets, and for anadromous fishes. Comparisons with SI models suggested that the scaled approach can overestimate the TL of top predators if ecosystem-specific information is not considered