Journal of Geography, Environment and Earth Science International

Artificial light at night (ALAN) is an increasingly widespread component of light pollution that alters natural light–dark conditions in aquatic environments. This review synthesises current knowledge on the sources and underwater propagation of ALAN, the factors influencing its effects, and reported biological and ecological responses across aquatic systems. Available evidence indicates that artificial illumination can modify biological rhythms, movement, feeding, predator–prey interactions, migration, reproduction, and habitat use in a range of aquatic and coastal organisms. Reported responses include changes in zooplankton diel vertical migration, altered activity and physiological performance in aquatic invertebrates and fishes, disruption of sea-turtle orientation and dispersal, effects on coral physiology and reproductive synchrony, and attraction or disorientation of seabirds. Because aquatic organisms are connected through food webs and exchanges between aquatic and terrestrial habitats, organism-level responses may extend to community composition, energy transfer, and ecosystem functioning. The ecological consequences of ALAN are influenced by light intensity, spectral composition, timing and duration of exposure, water optical properties, habitat characteristics, weather, season, and species-specific sensitivity. Although the evidence base is increasing, responses remain unevenly understood across taxa, habitats, and levels of biological organisation. Mitigation therefore requires careful control of light intensity, direction, spectrum, and timing, together with ecological monitoring and the integration of light-pollution considerations into freshwater, coastal, and marine conservation planning.