The taxonomic composition, numerical abundance, and biomass of the micro-zooplankton component of natural plankton populations from Saanich Inlet, British Columbia contained in large-volume (68 m3) Controlled Experimental Ecosystems (CEEs) were monitored during two studies
on the effects of copper. Populations subjected to 50 and 10 μg/l copper were examined along with two control populations in the first experiment; enclosures with copper at 10 and 5 μg/l and a single control were observed during the second experiment. Differences between
experimental and control CEE populations were greatest at the highest copper level, decreasing with lower concentrations. The major ciliate groups dropped out of the contained ecosystem with copper introduced at 50 μg/l and did not reappear. Oligotrich ciliates, but with different
dominant species than in the controls, developed in environments to which 5 and 10 μg/l copper had been added. Among the important micrometazoan taxa, naupliar copepod abundances were lower relative to the controls in 50 and 10 μg/l, but not 5 μg/l, copper-treated
enclosures. The observed effects on the micro-zooplankton taxa may not be related to direct action of copper on these organisms, but may have resulted from modifications to other trophic levels of the contained populations.
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