Short-Term Colonization of Rough and Smooth Tiles by Benthic Macroinvertebrates and Algae (Chlorophyll a) in Two Streams

Abstract

We examined the importance of substratum texture and the colonization dynamics of stream macroinvertebrates and algae (measured as chlorophyll a) using artificial substrata and two sampling designs in two ecologically different streams. Rough and smooth clay tiles were used in two short-term colonization studies, which were conducted in a 2nd-order Rocky Mountain foothill stream and a 2nd-order stream in the boreal mixed woodland of Alberta, Canada. At both streams, two sampling designs were used concurrently: (1) simultaneous placement and sequential removal of substrata, and (2) sequential placement and simultaneous removal of substrata. Three hypotheses were tested: there was no difference in the density of macroinvertebrates or quantity of chlorophyll a (1) on rough and smooth tiles, (2) for different colonization periods (1-14 d), and (3) for both sampling designs. Density of most macroinvertebrates and the quantity of chlorophyll a was greater on the rough tiles in both sampling designs and in both streams. Both sampling designs gave consistent results for the effect of texture for most taxa over eight colonization periods. Similar results for the sampling designs and in both streams provide strong evidence for the importance of substratum texture in streams. Some macroinvertebrate colonization patterns indicated early and late colonizers, while other patterns indicated no colonization trend. Several taxa showed similar trends in colonization to the quantity of chlorophyll a on the tiles. But after 1-4 d, when there was little chlorophyll a on the tiles (mean chlorophyll a < 0.1 μg/cm²), density of total number of organisms and most taxa was greater on rough tiles than on smooth tiles in both sampling designs. In contrast to most macroinvertebrates, Epeorus (Ephemeroptera: Heptageniidae) nymphs were more abundant on smooth tiles than on rough tiles.