Zooplankton in the Strait
Dave Mackas, Moira Galbraith, and Kelly Young, of Fisheries and Oceans Canada have compiled and analyzed historic zooplankton data dating back to 1990 for the Strait of Georgia.
Many of the dominant zooplankton taxa in the Strait of Georgia make extensive vertical migrations at daily and/or seasonal time scales. For this reason, the authors focused their analysis on the subset of samples that were collected at deep locations using net tows that sampled all or most of the water column. From 1990-1995 and 1998-2010, sampling by DFO and the Universities of Victoria and British Columbia provided a methodologically consistent and year-round set of time series samples. The authors have reported large decadal changes in the SOG zooplankton community.
The location of their sampling points within the Strait are shown in Figure 1. The SoG total zooplankton dryweight biomass is dominated by copepods (~40%) and euphausiids (~29%). Post 1990 time series for these two categories are shown in Figure 2. Along with many other zooplankton taxa, copepods and euphausiids had low biomass in 1994-95 and very low biomass in 2005-07.
Interannual variability of the entire zooplankton community is often summarized using a statistical technique called Principal Components Analysis (PCA). For the Strait of Georgia, nearly 36% of the total community variability projects onto the first principal component (time series shown in Figure 3a). This component had positive coefficients for nearly all of the zooplankton taxa (i.e. a positive PC1 score indicates above-average biomass for most taxa). It also correlated strongly with below average temperature in the Strait, and with a North Pacific climate index called the North Pacific Gyre Oscillation (NPGO) (Figure 3b).