Comparability of introduced tiles and natural substrates for sampling lotic bacteria, algae and macro invertebrates

SUMMARY.

• 1 Benthic microflora (bacteria and algae) and macro invertebrates on two types of introduced substrates, unglazed clay tiles and sterilized rocks, were compared quantitatively with natural rocks in a third-order stream. Big Sulphur Creek, California, U.S.A.
• 2 Exposure periods ranging from 28 to 153 days for introduced substrates indicated that tiles accurately represented bacterial density, chlorophyll a, and macro invertebrate density and species composition of natural rocks within 28 days; phaeophytin and total organic material (as ash-free dry weight) were accurately represented within 63 days. In contrast. sterilized rocks required a 63 day exposure to simulate most of the above natural-rock features.
• 3 Tiles reduced sampling variability (i.e. increased precision) when compared with either natural or sterilized rocks, especially the variability associated with algal measurements. In benthic studies where a sufficiently long exposure period is possible (1-2 months), introduced substrates can reduce the effort and cost of benthic sampling while minimizing habitat disruption.