Using an optical plankton counter to measure fine-scale and seasonal variation in the size-distribution of zooplankton communities




Bird, Tomas Joda.

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The use of an optical plankton counters in zooplankton ecology requires sampling strategies and hypothesis testing that take into account its ability to collect highresolution size-structured data, as well as its inability to distinguish zooplankton from detritus. Studies in Saanich Inlet and the Strait of Georgia, B.C. were performed to 1) compare the temporal resolution of OPC and net samples and 2) compare seasonal variation in the zooplankton community size structure against the predictions of biomass size distribution theory. The first part of this work found that OPC samples have finer resolution and require fewer replicates to approximate the mean abundance of zooplankton than net samples at time scales between 20 minutes and 48 hours. However, the OPC is subject to measurement error in high productivity waters. The second section of this work shows that the size-spectrum dynamics of zooplankton in the Strait of Georgia follow the predictions of biomass size spectrum theory. The interpretation of thse data using size-distribution theory suggests that variation in the trophic dynamics of the zooplankton community may be at the root of the observed seasonality.