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 approximate to 8% in temperate regions over the p ast decade, but little effort has been devoted to understanding the ec ological effects on temperate ecosystems. This research examined the e ffects 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 Ark ansas 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 us ed in these experiments were similar to levels that stream organisms e xperience during clear, mid-day conditions at Fort Collins, Colorado ( longitude 105 degrees 30'; latitude 40 degrees 35'). 3. Drift was sign ificantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddi sflies) 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 partic ularly sensitive to predicted increases in UV radiation, because strea ms are generally shallow with clear water. As a result of this potenti al sensitivity, we recommend that research be directed to understandin g the ecological effects of UV radiation on these habitats.