The behavioral responses of 2 Appalachian crayfish to cool and warm spectrum LED lights at night

Abstract

Ecological light pollution is increasing worldwide, but its threats to freshwater taxa and ecosystems are not well understood. Further, light-emitting diodes (LEDs) are currently replacing incandescent, fluorescent, and high-intensity discharge lights across much of the developed world. Cool-spectrum LED lights are characterized by shorter wavelength, cool-hued light, whereas warm-spectrum LED lights are characterized by longer wavelength, warm-hued light. It is unclear how spectral emissions produced by LED lights will affect freshwater animals, especially species with strong effects on stream ecosystems like crayfish. The New River crayfish (Cambarus chasmodactylus) and the spiny stream crayfish (Orconectes cristavarius) are important ecosystem engineers that can influence freshwater community structure. Here, we exposed these crayfish to cool (5000 K) and warm (3000 K) spectrum LED lights at ecologically-relevant intensities of 15 lx in a laboratory experiment. We recorded crayfish behaviors under each light treatment and in a dark control during the 1st and 3rd h after artificial dusk. We hypothesized that crayfish would reduce their activity and increase sheltering behavior under both light treatments. We found that O. cristavarius sheltering behavior significantly increased while exposed to both cool and warm spectrum LEDs at 2000 h. The statistical differences in these results disappeared at 2200 h. Cambarus chasmodactylus increased sheltering behavior in response to cool spectrum LEDs but not to warm spectrum LEDs at 2000 h. However, this pattern was reversed at 2200 h. The overall trend was that crayfish reduced their activity under artificial lights at night, although the responses of the 2 species varied somewhat. If crayfish activity is reduced by artificial lights at night, the effects of crayfish on aquatic systems may be altered in areas with extensive light pollution.