Midwest Fish & Wildlife Conference 2018

AUTHORS. Kyle Broadway, Thomas Detmer, Cal Potter, Scott Collins, Joseph Parkos III, David Wahl - Illinois Natural History Survey

ABSTRACT. The process of enumerating, identifying, and measuring zooplankton has traditionally been accomplished through microscopy, which can be time intensive and accrue high-cost over time. The development of fully or semi-automated methods are becoming viable and potentially cost-effective alternatives to historic approaches. Although such approaches are increasing in frequency for characterizing phytoplankton communities, they are less common for 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. Additionally, we developed a new technique for estimating zooplankton body mass using profile area instead of length. An estimate bias of reduced size by the semi-automated approach to true size resulted, which we determined to be caused by incomplete body images. However, body mass estimation from mean profile area was similar to mass estimates from a commonly used, literature derived length to mass regression. A strong relationship was observed between the semi-automated approach and microscopy derived abundances. We detected a subtle bias from the semi-automated method and subsequently developed a correction factor. Similarly, community composition did not differ among methods. Under most conditions evaluated, the semi-automated approach yielded a time-cost savings of approximately 38% compared to a traditional microscopy method, but lower in detrital rich samples. This study highlights the need to validate new protocols thoroughly before they are used, as there is potential for bias among methods. With corrections, semi-automated methods represent a viable and cost-effective alternative to traditional microscopy methods for the processing of zooplankton samples.