Zooplankton trace metal accumulation in the Strait of Georgia : trends, sources and insights

The Strait of Georgia (SoG) is a highly productive, semi-enclosed body of water located in the Northeast Pacific Ocean. However, increasing anthropogenic metal pollution may pose a threat to SoG organisms. To investigate metal accumulation in zooplankton, we sampled a time series station (49°15.00’ N, 123°40.00’ W) four times between 2017 and 2018. Using trace metal techniques, we measured dissolved (Ag, Cu, Cd) and particulate trace metals (P, Al, Ag, Cu, Cd), and zooplankton community composition, size-fractionated trophic position, and carbon and trace metal content (Ag, Ba, Cd, Co, Cr, Cu, Mn, Ni, Fe, and Zn). We also calculated zooplankton metals’ bioaccumulation factors (BAFs; zooplankton the metal content (mg ∙ kg d.w.-¹) divided by seawater dissolved metal concentration (mg ∙ L-¹)). Zooplankton were found to be mainly omnivores, and dominated by the calanoid copepod Metridia pacifica. The average content of metals in zooplankton (mg ∙ kg d.w.-1) was: Fe >> Zn ≥ Mn ≥ Ba > Cu > Ni > Cd ≥ Cr > Co ≥ Ag. Higher concentrations for Cu, followed by Cd, and Ag were also found in the dissolved and particulate phases in seawater. In contrast, zooplankton BAFs were Ag >> Cu > Cd. The zooplankton content and BAFs of these metals varied seasonally, but no systematic trends could be identified. We hypothesize that Ag BAFs were highest because of high Ag bioavailability in seawater, and its remarkable propensity to bind soft bases, such as thiolates, relative to essential metals (i.e., Cu, Zn). The results of an applied bio-energetic kinetic model indicate that the majority of Ag, Cu, and Cd assimilated by SoG zooplankton is derived from non-lithogenic particles. Current total concentrations of Cu, Ag, and Cd in SoG do not exceed long-term chronic concentrations reported in the BC Water Quality Guidelines. However, several Ag and Cd zooplankton content measurements surpassed the toxicity threshold reported to hinder reproduction. Based on the tendency of Ag and Cd to scavenge to particles in oxic and anoxic environments, respectively, these metals could pose a threat to the wellbeing of SoG zooplankton and should be carefully monitored.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat