Comparison of microscopy to a semi-automated method (FlowCAM®) for characterization of individual-, population-, and community-level measurements of zooplankton

Fully or semi-automated methods are becoming viable, cost-effective alternatives to manual approaches for characterizing zooplankton. The goal of this study was to compare a semi-automated approach (FlowCAM®) and a traditional microscopy method for characterizing zooplankton body size, density, and community structure. We demonstrate that estimating mass from FlowCAM® profile area had similar accuracy to a commonly used length to mass regression model. FlowCAM® and microscopy produced related length measurements for Daphnia, Calanoida, and Cyclopoida. Length measurements of rotifers, nauplii, and Sididae were not significantly related between the two methods, likely because of high morphological variation within taxa. Density comparisons between methods indicated high correlation between the semi-automated approach and microscopy-derived densities with a subtle bias of lower densities with the semi-automated method. After applying a correction factor, independent samples showed similar density estimates between methods, with community composition also not differing between methods. Comparison of processing time between the two methods showed that the semi-automated approach was 11 min (33%) faster per sample. With corrections, semi-automated methods represent a viable and cost-effective alternative to traditional microscopy methods for the processing of zooplankton samples.