Natural Cd and Pb variations in Mytilus californianus during the upwelling season

The short term variability of Cd and Pb in Mytilus californianus in relation to upwelling events was studied. Sea water and mussel samples were taken daily for 4 weeks during the upwelling season (late summer) on the west coast of Vancouver Island. Upwelling indicators (PO4, T and S) were measured and related to the variations in dissolved Cd and Pb in sea water. High variability in Cd and Pb mussel concentrations were detected, with significant differences found from one day to another. After normalizing, to account for the variability due to the condition of the mussel, significant differences among samples were still detected. The differences in mussel Cd were associated with the variations in dissolved Cd due to upwelling. Mussel Pb, however, was not related to variations in dissolved Pb. Principal component analysis was used to unravel patterns of variation among all variables measured. Parallel to the sampling of natural mussel beds, a transplant experiment was performed to compare the variability of intertidal vs. subtidal mussels. The transplanted mussels exhibited a less variable condition index and revealed more clearly the relation of dissolved Cd with the concentrations in the mussels. Lead in mussels, again, did not show a relationship with dissolved Pb. In addition, the mantle edge (from 3 days with highest and lowest Cd concentrations) was analyzed as an alternative indicator which could exhibit less variability. The Cd variability in the mantle edge was compared with that of the gills and the remainder. The mantle edge, even though it showed less variability than the gills and the remainder, still exhibited significant differences between days.