Abstract: The present review draws together wide-ranging studies performed over the last decades that catalogue the effects of artificial-light-at-night (ALAN) upon living species and their environment. We provide an overview of the tremendous variety of light-detection strategies which have evolved in living organisms – unicellular, plants and animals, covering chloroplasts (plants), and the plethora of ocular and extra-ocular organs (animals). We describe the visual pigments which permit photo-detection, paying attention to their spectral characteristics, which extend from the ultraviolet into infrared. We discuss how organisms use light information in a way crucial for their development, growth and survival: phototropism, phototaxis, photoperiodism, and synchronization of circadian clocks. These aspects are treated in depth, as their perturbation underlies much of the disruptive effects of ALAN. The review goes into detail on circadian networks in living organisms, since these fundamental features are of critical importance in regulating the interface between environment and body. Especially, hormonal synthesis and secretion are often under circadian and circannual control, hence perturbation of the clock will lead to hormonal imbalance. The review addresses how the ubiquitous introduction of light-emitting diode technology may exacerbate, or in some cases reduce, the generalized ever-increasing light pollution. Numerous examples are given of how widespread exposure to ALAN is perturbing many aspects of plant and animal behaviour and survival: foraging, orientation, migration, seasonal reproduction, colonization and more. We examine the potential problems at the level of individual species and populations and extend the debate to the consequences for ecosystems. We stress, through a few examples, the synergistic harmful effects resulting from the impacts of ALAN combined with other anthropogenic pressures, which often impact the neuroendocrine loops in vertebrates. The article concludes by debating how these anthropogenic changes could be mitigated by more reasonable use of available technology – for example by restricting illumination to more essential areas and hours, directing lighting to avoid wasteful radiation and selecting spectral emissions, to reduce impact on circadian clocks. We end by discussing how society should take into account the potentially major consequences that ALAN has on the natural world and the repercussions for ongoing human health and welfare.

Abstract: Due to the widespread use of artificial light, freshwater ecosystems in urban areas at night are often subjected to light of intensities exceeding that of the moonlight. Nocturnal dim light could modify fish behaviour and benefit visual predators because of enhanced foraging success compared to dark nights. However, effects of nocturnal light could be mitigated by the presence of structured habitats providing refuges for prey. We tested in laboratory experiments whether nocturnal light of low intensity (2 lx) increases foraging efficiency of the Eurasian perch (Perca fluviatilis) on invertebrate prey (Gammarus fossarum). The tests were conducted at dusk and night under two light regimes: natural cycle with dark nights and disturbed cycle with artificially illuminated nights, in habitats differing in structural complexity: sand and woody debris. We found that nocturnal illumination significantly enhanced the consumption of gammarids by fish compared to dark nights. In addition, the perch was as effective predator in illuminated nights (2 lx) as at dusk (10 lx). Woody debris provided an effective refuge only in combination with undisturbed darkness, but not in illuminated nights. Our results suggest that nocturnal illumination in aquatic ecosystems may contribute to significant reductions in invertebrate population sizes through fish predation. The loss of darkness reduces the possibility of using shelters by invertebrates and hence the effects of elevated light levels at night could not be mitigated by an increased habitat complexity.

Abstract: The toxic effects of silver nanoparticles (AgNP) to aquatic species and ecosystem processes have been the focus of increasing research in ecology, but their effects under different environmental stressors, such as the ongoing anthropogenic artificial light at night (ALAN) which can cause a series of ecological effects and will potentially interact with other stressors, remain poorly understood. Here, we aimed to assess the combined effects of AgNP and ALAN on the activities and community structure of fungi and bacteria associated to plant litter in a stream. The results showed that ALAN not only led to changes in the average hydrodynamic diameter, ζ-potential and dissolved concentration of AgNP but also inhibited the enzyme activities of leucine-aminopeptidase (LAP), polyphenol oxidase (PPO) and peroxidase (PER) associated to microbes involved in litter decomposition. The negative effect of AgNP on the decomposition of Pterocarya stenoptera leaf litter was alleviated by ALAN owing to the reduction of Ag+ concentration in the microcosm and lignin content in the leaf litter in the A-AgNP treatments, the enhancement of β-glucosidase (β-G) activities and the increase of microbial biomass. The effect of ALAN alone or combined with AgNP or AgNO3 on the taxonomic composition of fungi was much greater than that on bacteria. Linear discriminant analysis effect size (LEfSe) demonstrated that each treatment had its own fungal and bacterial indicator taxa, from the phylum to genus levels, indicating that the microbial communities associated with litter decomposition can change their constituent taxa to cope with different stressors. These results reveal that ALAN can decrease the toxicity of AgNP and highlight the importance of considering ALAN during the assessment of the risk posed by nanoparticles to freshwater biota and ecosystem processes.