Temporal and Spatial Distribution of the Harmful Diatoms Chaetoceros concavicornis and Chaetoceros convolutus along the British Columbia Coast

Abstract

The harmful phytoplankters Chaetoceros concavicornis and Chaetoceros convolutus are normal components of the phytoplankton assemblage along the British Columbia coast. During 1988, these diatoms occurred at their highest concentrations in the spring and fall from the Strait of Georgia to Queen Charlotte Strait. North of Queen Charlotte Strait, the maximal concentrations appeared to be delayed until summer. The greatest concentrations occurred in the waters of the Strait of Georgia and its contiguous bays and inlets, especially Jervis Inlet, where concentrations of C. concavicornis and C. convolutus which could be harmful to salmon occurred during the spring and fall of 1988. Lesser concentrations occurred in coastal seawaters north of the Strait of Georgia. These phytoplankters were absent, or were present in only minor concentrations, in inlets with low-salinity waters such as Holberg Inlet and Indian Arm. Harmful Chaetoceros cells were restricted to seawaters greater than approximately 17‰ salinity. Vertically and horizontally well-mixed waters, such as those of Johnstone Strait, also appeared to restrict the presence of these cells. The greatest concentrations of these diatoms occurred during the spring and fall in relatively stratified coastal seawater with salinities between 26 and 34‰.