An improved technique for sampling lotic invertebrates

Abstract

Sampling of individual stones to quantify benthic community structure has several advantages over traditional area-restricted samplers. Processing effort can be reduced, and density and error estimates that account for variation due to substratum heterogeneity and dispersion of organisms can be determined. Although the Doeg & Lake stone sampler is used to collect stream fauna from stones, our preliminary observations suggested that this sampler overestimated invertebrate density. A U net sampler is described that produces more accurate estimates of faunal density of individual stones. Performances of the U net and Doeg & Lake stone sampler were evaluated by collecting invertebrates from replicate cobbles (maximum diameter 128–256 mm) within a fourth-order stream and comparing respective estimates of invertebrate density, sample variance, and relative abundance. The Doeg & Lake sampler consistently overestimated invertebrate density compared with estimates from the U net. Differences in density estimates were due to increased disturbance of invertebrates due to placement of the Doeg & Lake sampler on the substratum compared to the U net technique. The number of taxa, species diversity (H') and sample variation collected from cobbles with the two samplers were similar. By isolating the fauna of individual stones; the U net produced accurate estimates of density and relative abundance of taxa. The U net sampler is an effective tool for collecting quantitative samples of stream macroinvertebrates because it can be used to quantify invertebrate faunas of large substrata where traditional, area-restricted samplers are ineffective.