Influence of ultraviolet-B radiation on the drift response of stream invertebrates

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet‐B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms. 2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid‐day conditions at Fort Collins, Colorado (longitude 105°30′; latitude 40°35′). 3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB‐exposed streams may be a behavioural response and/or a result of injury. 4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.