Into the light: the adverse effects of artificial light at night on nest density of olive ridley sea turtles (Lepidochelys olivacea)

Abstract

Light pollution caused by artificial light at night (ALAN) is an increasing threat to biodiversity, particularly in coastal ecosystems where human population density is high. In this study, we evaluated the impact of ALAN on the nest density of olive ridley sea turtles ( Lepidochelys olivacea ) along a 7.5 km beach transect on the Pacific coast of Guatemala. Using a lux meter to measure light intensity at 237 sites over two nesting seasons (2021–2022), we analyzed whether ALAN has adverse effects on nest density. Our findings revealed that nest density was lower with higher levels of ALAN. Each one-unit increase in lux corresponds to a 29–34% reduction in expected nest counts. Additionally, we observed a “weekend effect” on nest density, with lower nest densities on weekends, coinciding with higher light levels and likely greater human presence. Although light levels were slightly lower in 2022, nest density declined, suggesting that additional environmental or ecological factors influenced nesting activity between years. These results reinforce the ecological importance of environments with little human activity and low levels of ALAN for nesting sea turtles, underscoring the need for targeted mitigation strategies. We also highlight methodological limitations and recommend incorporating species-specific light sensitivity into future monitoring programs and coastal lighting mitigation efforts.