Establishing reliable minimum count sizes for cladoceran subfossils sampled from lake sediments

Abstract

The effects of low counts on assemblage inferences in paleolimnological investigations have been examined for many biological proxies, but not yet for Cladocera. Established guidelines leading to the determination of an adequate, minimum count are absent with respect to sampling cladoceran remains from lake sediments. Using simulated subsamples derived from observed assemblages of considerably higher counts, we investigated the effect of counting effort on three principal characteristics of an assemblage: richness, number of new taxa encountered, and the absolute differences in relative abundances of dominant taxa. Results from six lakes located within diverse ecological regions (i.e. Subarctic, Canadian Shield, Acadian Forest) suggest that a minimum of between 70 and 100 individuals is satisfactory to characterize most assemblages. Doubling counting effort from 100 to 200 individuals leads to only modest gains in subsample relatedness to the observed assemblage. Greater counting effort may be necessary when the primary interest is in presence-absence or distributional data, or when abundances of ecologically relevant taxa are exceptionally low.