The effect of artificial light at night on sea turtle hatchling early dispersal: A systematic review of methods, impacts and findings

Artificial light at night (ALAN) is a rapidly expanding pollutant, raising concerns about its impact on species that rely on natural light cues for critical behaviours, such as for sea turtle early dispersal. After emergence, sea turtle hatchlings orient themselves using natural light cues to quickly crawl to the ocean (sea-finding) and swim offshore. Numerous studies have shown that artificial light disrupts their capacity to orient during their early dispersal with varying consequences, although variability exists in the methodologies used and the results. Here, we systematically reviewed the literature (74 publications) to summarise the methods and findings on the impacts of ALAN on sea turtle hatchlings during early dispersal. The review highlights key findings on how hatchling orientation during early dispersal is disrupted by different light types, light intensity, and distance to the light source. We review the visual capabilities of sea turtles and relate this ability to their behavioural attraction to different light types. Additionally, we discuss the availability of empirical evidence for energetic, behavioural, and physiological costs and consequences of disrupted orientation, along with management strategies that have been proposed to reduce the risk posed by ALAN. We conclude that more studies measuring the consequences of disrupted orientation are required to determine the long-term impacts of artificial lighting for turtle populations. Further, we suggest that research move towards identifying light intensity thresholds for artificial lights of different spectra and develop light exclusion zones to assist with management and promote best practice for lighting in coastal areas to protect these endangered species.