Light pollution is omnipresent in modern society and is seriously disrupting marine ecosystems.Researchers are highlighting its effects on certain fish and the changes in their behaviour in just a few nights. More alarmingly, these changes can also be seen in their offspring. Reinforced by other research on insects and birds, these discoveries underline the urgent need to limit light pollution.Concrete measures are needed to protect biodiversity and restore the fragile natural balance.
By Laurie Henry
Artificial light in nocturnal environments has transformed urban and rural landscapes, disrupting the natural rhythms of ecosystems. Night-time lighting, whether it comes from urban infrastructures or from our domestic screens, disrupts the biological cycles of many species. A recent study, published in the journal Science of the Total Environment by researchers from the Max Planck Institute of Animal Behavior and theInstitute of Hydrobiology of the Chinese Academy of Sciences, highlights the unexpected consequences of this pollution on zebrafish (Danio rerio). This work reveals profound and transgenerational behavioural changes linked to nocturnal exposure to light sources, particularly in the blue spectrum.
Fish on the front line
Zebrafish are a model commonly used in behavioural and environmental biology. The research focused on artificial light levels simulating the intensity of urban lighting such as street lamps. These levels, corresponding to around 20 lux, are typical of the illuminated environments to which many species are exposed. The aim was to understand how these conditions disrupt natural biological cycles, focusing on short-term behavioural changes and their possible implications for the next generation.
To carry out this study, the researchers designed a rigorous protocol to simulate conditions of exposure to artificial light at night. They used 400 female zebrafish, a species widely studied for its sensitivity to environmental stimuli. The fish were placed in aquariums and exposed to ten different light regimes, including nine wavelengths of the visible spectrum (from red to blue) and a standard white light, commonly emitted by urban lighting. Each light regime was calibrated at 20 lux, a light intensity typical of streetlights and close-range electronic devices. For eight consecutive nights, the fish were kept under these conditions in order to analyse the effects of their prolonged exposure to different colours of light.
Effects of different wavelengths of light on fish according to (a) their distance travelled to the walls (in cm) and (b) their activity rate (in %). © Weiwei Li,et al., 2024To assess the behavioural impact, the researchers used a sophisticated automated tracking system capable of accurately measuring the movements of the fish and their positioning in the aquarium. This monitoring enabled signs of anxiety to be identified, including a significant reduction in movements, increased grouping of individuals and marked thigmotaxis (when fish spend more time close to the walls, a response commonly associated with stress). These behaviours were observed under all light conditions, but the most pronounced and rapid effects were recorded under exposure to blue light (470 nm), which causes signs of anxiety as early as the fifth night. These observations reflect the disproportionate impact of blue light (often emitted by screens or LEDs) on the biological cycles and natural behaviours of animals.
Trans-generational damage
The impact on the offspring of these zebrafish was then closely examined. After female zebrafish were exposed to artificial light at night, their offspring displayed atypical behaviour, despite being reared under natural light conditions. The larvae from these females showed a significant reduction in their daytime activity, as measured by automated monitoring software. This result shows that the behavioural impacts of light pollution are not limited to direct exposure, but are also passed on to offspring. Ming Duan, co-author of the study, points out that these behavioural changes could affect the ability of young fish to survive in their natural environment, particularly by reducing their ability to explore, feed or avoid predators.
A zebrafish © Pixabay
These results therefore point to epigenetic mechanisms, where environmental modifications influence gene expression without modifying their structure. Aneesh Bose, also co-author of the study, suggests that sleep deprivation caused by exposure to light plays a key role in this transmission. Fish exposed to artificial light, particularly in the blue spectrum, undergo a prolonged disruption of their circadian cycles, resulting in chronic biological stress. This stress could reset certain epigenetic processes in the reproductive cells of females and thus directly affect the behavioural development of their offspring. This hypothesis opens up new prospects for studying the lasting impact of light pollution on ecosystems.
Worrying ecological implications
Artificial light also modifies natural habitats, particularly in coastal and riparian areas where many aquatic species depend on natural light cycles for their biological behaviour. These ecosystems, often located close to human activities, are subject to continuous night-time lighting from urban infrastructures, street lamps and industrial installations. This light intrusion alters the circadian rhythms of organisms, which are essential for processes such as reproduction, migration and feeding. For example, certain species of fish, crustaceans and aquatic insects, which are sensitive to blue light, have their behaviour altered, disrupting food chains and predator-prey interactions. The consequences of these imbalances could spread to other species in surrounding ecosystems, exacerbating the cumulative effects of light pollution.
Faced with this threat, scientists are stressing the urgent need to adopt practical measures to limit the impact of artificial lighting. One of the most promising solutions is to reduce light intensity and restrict the use of wavelengths in the blue spectrum, which are particularly harmful to wildlife. According to Ming Duan, priority should be given to adjustments in areas close to natural habitats. These measures would include the installation of ground-oriented luminaires, the use of filters or technologies that reduce light diffusion, and strict regulation of night-time lighting in protected areas. Such adjustments would contribute not only to the preservation of aquatic ecosystems but also to the sustainable management of interactions between human activities and the environment.
These results underline the need for dialogue between researchers, decision-makers and citizens to adopt responsible practices. As Li concludes: ‘ We have the capacity to act now to protect not only current ecosystems, but also future generations ’.
Source : Weiwei Li,et al., “Behavioural and transgenerational effects of artificial light at night (ALAN) of varying spectral compositions in zebrafish (Danio rerio)”. Science of The Total Environment, 2024; 954: 176336 DOI: 10.1016/j.scitotenv.2024.176336