We investigated the importance of shrimps (Atyidae and Palaemonidae) and ephemeropterans (Baetidae) in the removal of periphyton and sediments in a Neotropical stream. The experimental site was open with homogeneous bedrock, shallow depth (8–15 cm), and intermediate water current velocity (0.2–0.3 m/s). We used 2 intensities of electrical current to exclude both shrimps and ephemeropterans (high-intensity treatment) or only shrimps (low-intensity treatment) from fixed areas (180 × 30 cm) of bedrock. When both ephemeropterans and shrimps were excluded in 2 experiments, matter accumulated on the bedrock to 5 and 20× the level in controls; when only shrimps were excluded, no accumulation was observed. Chlorophyll a increased significantly in the high-intensity exclusion, but most of the accumulation was fine organic and inorganic matter. In experiment 1, benthic matter and chlorophyll a decreased by an order of magnitude in areas in which ephemeropterans increased ∼40×. The increase in ephemeropterans was associated with a reduction in shrimp activity. In experiment 2, no increase in ephemeropterans was observed. Palaemonid shrimps (Macrobrachium olfersi) were more common than atyid shrimps (Potimirim glabra) in the study area. Therefore, we assumed that Macrobrachium, rather than Potimirim, interacted negatively with ephemeropterans and that Macrobrachium did not remove periphyton. We concluded that baetid ephemeropterans (particularly Americabaetis sp.) were the most important grazers and removers of benthic matter in this system.
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