Artificial light at night reduces predation and herbivory rates in a nearshore reef.

Artificial light at night (ALAN) is an escalating anthropogenic stressor that can affect ecological communities over a range of spatial scales by altering key ecological processes, such as predation and herbivory. Shallow subtidal reefs are highly diverse and productive habitats that are vulnerable to ALAN. We investigated rates of consumption by fish (predation and herbivory) under different light treatments (ALAN, dark and daylight conditions) using standardised bioassay methods, i.e. squidpops and Ulva pops in situ. We also used GoPros to record predator identity, number of strikes and time to strike in ALAN and daylight treatments. Contrary to previous studies, we found that predation and herbivory rates were significantly lower in ALAN treatments than in daytime and dark treatments. The highest predation and herbivory rates were observed in daytime treatments. The identity of predator species, time to strike and number of strikes also differed between daytime and ALAN treatments. Due to low light conditions, dark treatments were not filmed. Our findings suggest that ALAN can alter predation in unexpected ways, depending on the environmental conditions and species affected. Future coastal management strategies need to account for light pollution as a major stressor to preserve valuable ecological resources.