A comparative analysis of zooplankton field collection and sample enumeration methods

Abstract

Understanding differences in zooplankton abundance depends on comparing similar data. Scientists employ numerous methods to collect and count freshwater zooplankton, potentially leading to difficulties when comparing studies. As scant information concerning specific biases exists, we quantified how (1) net mesh size and (2) counting techniques influence zooplankton size and abundance estimates. We compared mesh sizes by collecting zooplankton with four vertically hauled nets differing only in mesh size. We examined mesh‐size effects on filtration efficiency across a suspended sediment gradient by comparing the known (quantified with a flowmeter) and assumed (from site depth) sample volumes. Finally, eight samples were counted with each of four methods to compare estimates of zooplankton abundance among techniques that differ in the minimum number of individuals counted. We found that only 64‐µm mesh nets effectively capture small‐bodied zooplankton (small cladocerans, copepod nauplii, and rotifers, mean size = 0.13−0.30 mm) whereas all nets effectively collected larger‐bodied zooplankton (mean size > 0.48 mm). All three > 100 µm‐mesh nets were > 90% efficient, regardless of suspended solids abundance. In contrast, the 64‐µm mesh net was at best 60% efficient; hence, actual volume sampled must be determined to avoid underestimation. We found counting‐method‐specific shortcomings, particularly for those in which few individuals were counted. We recommend, then, that a moderate number of individuals are counted for many finely resolved taxonomic categories or many individuals are counted for fewer, broader taxonomic categories. Consequently, to directly compare zooplankton densities between studies, scientists need a clear understanding of field collection and laboratory enumeration methods.

Effect of agricultural landscape characteristics on the hydrobiota structure in small water bodies

“…All cladocerans were identified to species level, while rotifers to the level of species in most cases and to genus for a restricted set of soft-bodied taxa which contract during sample preservation. Counting of zooplankton was performed in accordance with standard techniques recommended for this group of organisms (Mack et al, 2012).…”

Context‐dependent planktivory: interacting effects of turbidity and predation risk on adaptive foraging

“…The net used at the Huron site had 63-lm mesh. The use of different mesh sizes in these exact nets has been shown to have no effect on the estimation of abundance for the zooplankton taxa primarily consumed by age-0 yellow perch used in this study (i.e., crustacean zooplankton larger than rotifers and copepod nauplii; Mack et al 2012). All zooplankton was preserved in 70% ethanol (EtOH) until laboratory analysis.…”

Environmental Stress Responses and Experimental Handling Artifacts of a Model Organism, the Copepod Acartia tonsa (Dana)

“…For field studies, it is often impossible to know how long the copepods may have been in contact with a plankton net during collection and before preservation (e.g., Mack et al, 2012). According to the field guide by Goswami (2004), it is FIGURE 5 | Heat map of differentially expressed genes (q < 0.05) for the handling stress and salinity shock treatments 15 min post exposure relative to the control.…”

“…Based on the observed mortalities, we chose the exposure time of 10 min for each stressor, which is within the range of handling time described in published studies, although sufficient to ensure that we would induce a transcriptional response (Elliott and Tang, 2009;Mack et al, 2012). …”