Zooplankton sampling in riverine systems: a gear comparison in the Upper Mississippi River

Abstract

Standardization of methods is important to allow for comparisons of data through time and space, across studies, and to increase replicability of research. Zooplankton research in large river systems is sparse and sampling methods have rarely been evaluated. The USEPA recommends using a pump to collect a total of 180 L of river water for macrozooplankton (>63-μm), yet researchers continue to use a wide variety of sampling gear and collect lower sample volumes for their analysis. Variations in sampling methods make it difficult to compare zooplankton within and across systems, presenting the need for a standard collection method to be developed through scientific evaluation and enforced for future monitoring efforts. We compared community estimations between four sampling devices (Shindler-Patalas trap, integrated tube sampler, diaphragm pump, and horizontal tow net) to determine the best gear that collects the greatest abundances/L, highest species richness, and the most replicable samples. Next, we evaluated different sample volumes and their impact on abundance/L estimates, rate of detection, and variance within replicates. The powered pump most consistently yielded the highest abundances and most replicable collections, and large sample volumes (30-40L) are most appropriate for zooplankton monitoring in large river habitats.