Abstract
Artificial lighting at night (ALAN) produced by urban, industrial, and roadway lighting, as well as other sources, has dramatically increased in recent decades, especially in coastal environments that support dense human populations. Artificial “lightscapes” are characterized by distinct spatial, temporal, and spectral patterns that can alter natural patterns of light and dark with consequences across levels of biological organization. At the individual level, ALAN can elicit a suite of physiological and behavioral responses associated with light-mediated processes such as diel activity patterns and predator-prey interactions. ALAN has also been shown to modify community composition and trophic structure, with implications for ecosystem-level processes including primary productivity, nutrient cycling, and the energetic linkages between aquatic and terrestrial systems. Here, we review the state of the science relative to the impacts of ALAN on estuaries, which is an important step in assessing the long-term sustainability of coastal regions. We first consider how multiple properties of ALAN (e.g., intensity and spectral content) influence the interaction between physiology and behavior of individual estuarine biota (drawing from studies on invertebrates, fishes, and birds). Second, we link individual- to community- and ecosystem-level responses, with a focus on the impacts of ALAN on food webs and implications for estuarine ecosystem functions. Coastal aquatic communities and ecosystems have been identified as a key priority for ALAN research, and a cohesive research framework will be critical for understanding and mitigating ecological consequences.
Highlights
Artificial lighting at night (ALAN) alters natural patterns of light and darkness by introducing light that varies in intensity and spectral composition during typically dark periods (Gaston et al 2013)
Here we focus on potential effects of ALAN on diel activity patterns, light plays a key role in physiological and molecular pathways that influence seasonal breeding, migration, and orientation
Based on our review and synthesis of documented ALAN impacts from individuals to communities and ecosystems, we conclude by proposing the following key research avenues, which we offer as the basis for development of a cohesive research framework: 1. Characterizing natural diel and seasonal light changes in estuarine habitats will help predict ALAN impacts and inform management of artificial light use
Summary
Artificial lighting at night (ALAN) alters natural patterns of light and darkness by introducing light that varies in intensity and spectral composition during typically dark periods (Gaston et al 2013). Melatonin (a hormone involved with regulating daily physiological and behavioral activities) is upregulated in diurnal animals with the onset of dark, leading to decreased activity, but under ALAN, melatonin production may be inhibited by the artificial light signal (Ouyang et al 2018) This can have profound effects on timing of activities, which are typically adapted to be optimal at particular times of the day or night (e.g., when food is most available), potentially resulting in reduced fitness. Altered underwater light environments are known to contribute directly to the loss of biodiversity in aquatic systems, for example via disruption of visual signals used for mate choice during reproduction (van der Sluijs et al 2011) In these cases, light intensity was decreased, and color content shifted due to elevated turbidity levels; since ALAN provides more light at night, and in particular broad-spectrum light that allows for color-mediated behaviors, it is unclear if reproductive output will always be compromised directly. ALAN disrupts orientation of sea -turtle hatchlings, yet it may
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