title: Artificial light and nocturnal activity in gammarids.
abstract: Artificial light is gaining attention as a potential stressor to aquatic ecosystems. Artificial lights located near streams increase light levels experienced by stream invertebrates and we hypothesized light would depress night drift rates. We also hypothesized that the effect of light on drift rates would decrease over time as the invertebrates acclimated to the new light level over the course of one month's exposure. These hypotheses were tested by placing Gammarus spp. in eight, 75 m × 1 m artificial flumes. One flume was exposed to strong (416 lx) artificial light at night. This strong light created a gradient between 4.19 and 0.04 lx over the neighboring six artificial flumes, while a control flume was completely covered with black plastic at night. Night-time light measurements taken in the Berlin area confirm that half the flumes were at light levels experienced by urban aquatic invertebrates. Surprisingly, no light treatment affected gammarid drift rates. In contrast, physical activity measurements of in situ individually caged G. roeseli showed they increased short-term activity levels in nights of complete darkness and decreased activity levels in brightly lit flumes. Both nocturnal and diurnal drift increased, and day drift rates were unexpectadly higher than nocturnal drift.
authors.affiliation: Leibniz Institute of Freshwater Ecology and Inland Fisheries , Berlin , Germany ; Institute of Biology, Freie Universität Berlin , Berlin , Germany.
authors.forename: Elizabeth K
authors.initials: EK
authors.lastname: Perkin
authors.affiliation: Leibniz Institute of Freshwater Ecology and Inland Fisheries , Berlin , Germany.
authors.forename: Franz
authors.initials: F
authors.lastname: Hölker
authors.affiliation: Leibniz Institute of Freshwater Ecology and Inland Fisheries , Berlin , Germany ; Umweltbundesamt , Berlin , Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Heller
authors.affiliation: Umweltbundesamt , Berlin , Germany.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Berghahn
keywords: Acclimation; Gammarus; Invertebrate drift; Light pollution; Multispecies freshwater biomonitor