Light pollution may alter host–parasite interactions in aquatic ecosystems.

Impacts of artificial light at night on wildlife are well documented, yet specific effects on parasitism in aquatic systems are largely unknown. Circadian patterns in animal physiology and behaviour are light-driven, as is host-searching by many infective stages. This can be impacted by artificial light at night. Attraction of hosts and infective stages to light sources can result in aggregations that promote direct infection by infective stages and high levels of trophic transmission. I hypothesise that temporal fluctuations in infection risk disappear as day–night differences in lighting are reduced, that areas exposed to light at night act as hotspots of transmission, and that altered photoperiod exerts strong selective pressures. Known effects of light on host–parasite interactions must be considered when designing measures to reduce the impact of artificial light on wildlife. With growing human populations living along freshwater shores and marine coastlines, aquatic ecosystems are experiencing rising levels of light pollution. Through its effects on hosts and parasites, anthropogenic light at night can disrupt host–parasite interactions evolved under a normal photoperiod. Yet its impact on aquatic parasites has been ignored to date. Here, I discuss the direct effects of light on the physiology and behaviour of parasite infective stages and their hosts. I argue that night-time lights can change the spatiotemporal dynamics of infection risk and drive the rapid evolution of parasites. I then highlight knowledge gaps and how impacts on parasitic diseases should be incorporated into the design of measures aimed at mitigating the impact of anthropogenic light on wildlife. [ABSTRACT FROM AUTHOR]