Collection strategies for quantifying protist assemblages in temperate headwater streams

Abstract

The determinination of an adequate col- lection protocol for protists is critical in the examina- tion of their distribution and composition in temperate headwater streams. The objective of this study was to test which sampling design/sample gear combination would yield a cost-effective, site-representative protist assemblage. Defining parameters included greatest taxa richness, abundance, morphological diversity, taxa overlap, and cell-size diversity. Two sample designs (i.e., transect and mesohabitat design) and two sample gears (i.e., benthic grab sample, and a coloniz- ing device (polyurethane foam unit, PFU)) were tested in three 100-m reaches representing the predominant environmental conditions (i.e., fragmented woodlots and agriculture) in the study area. A two-way ANOVA was used to evaluate abundance taxa richness and abundance of the protist assemblage (fixed effects) across the three reaches (random effects). The meso- habitat sampling design had the highest mean in both taxa richness (n = 72, P = 0.0012) and abundance (n = 72, P = 0.0004). The highest mean was reported with the benthic grab sampler (39.89 ± 1.1) in the abundance count only (n = 72, P \ 0.0001). There was no difference in the design and gear interaction. Morphological diversity, cell-size diversity and per- cent taxa overlap between sampling design/sample gear combinations also were examined. A higher taxa overlap of the top 10% most abundant taxa was observed with the benthic grab sampler (43-100%) versus the PFU (25-69%); however, the greatest morphological and cell-size diversity was produced by the transect design/PFU combination. We conclude a ''hybrid'' of the two sample designs will account for ''patchy'' distributional patterns of protists and use of the PFU, because of the highest yield in morphological and cell-size diversity, will provide the most cost- effective, site-representative protist assemblage in temperate headwater streams.