Artificial light at night causes unequal and species-specific shifts in infection risk by a generalist marine parasite

Abstract Light pollution, in the form of artificial light at night (ALAN), changes the normal physiology and behaviour of animals, leading to alterations in interspecific interactions. Parasitism is likely to be impacted, ranging from altered parasite proliferation and transmission to altered host exposure or susceptibility to infection. How these individual-level effects translate to higher level impacts remains poorly understood. Here, we used mesocosms to expose communities consisting of four crustacean species (two amphipods and two isopods) to a generalist microphallid trematode parasite capable of infecting all these species, maintained under three light treatments: control conditions with dark night-time, cold-white ALAN and warm-white ALAN. We observed contrasting changes in infection levels under cold-white ALAN conditions compared with the other two treatments. Amphipods were at a disproportionately higher risk of infections in the cold-white ALAN treatment. Although the relative abundance of the four species and thus the composition of communities were not significantly different among treatments at the conclusion of the experiment, parasite-induced mortality would be likely to differentially impact the smaller amphipods over longer periods. Our findings suggest that light pollution may indirectly alter community structure in shallow aquatic ecosystems through parasite-mediated effects.