Effects of spectral composition of artificial light on the colonization patterns of mobile epibenthic macrofauna in marinas.

Artificial light at night (ALAN) is an increasingly prevalent pollutant in anthropized coastal environments such as recreational marinas. While its impacts on sessile fouling are becoming better documented, those on mobile epibenthic macroinvertebrates remain limited. Here, we evaluated the effects of ALAN spectrum on the colonization patterns of mobile epibenthic macroinvertebrates. To address this issue, we conducted manipulative field experiments by exposing submerged artificial passive collectors to three light treatments in a recreational marina: cold and warm light, and unlit control. In a first experiment, collectors were retrieved after 3, 15 and 30 days to assess how ALAN affects the arrival and assemblage structure of early, intermediate and later colonizers. In a second experiment, collectors were either caged or left exposed and retrieved after 30 days to evaluate whether ALAN effects were mediated by fish predation. In the colonization experiment, total abundance, total biomass, and number of species increased under ALAN treatments after 3 days, but these differences disappeared after 30 days, except for total biomass, which remained higher. No significant differences were detected between both spectra. Multivariate analyses supported these patterns, revealing significant effects of ALAN on assemblage structure at early and late stages, but without detectable spectral differences in the colonization experiment. The predation experiment suggested greater effects of cold light than warm light in combination with predation, as well as a selective rather than overall predation effect on the assemblage. These insights may be considered for light pollution management in anthropized coastal habitats, such as recreational marinas.