Long-term exposure to artificial light at night in the wild decreases survival and growth of a coral reef fish

Schligler Jules, Cortese Daphne, Beldade Ricardo, Swearer Stephen E. and Mills Suzanne C. 2021 Long-term exposure to artificial light at night in the wild decreases survival and growth of a coral reef fish. Proc. R. Soc. B.2882021045420210454 http://doi.org/10.1098/rspb.2021.0454

Abstract

Artificial light at night (ALAN) is an increasing anthropogenic pollutant, closely associated with human population density, and now well recognized in both terrestrial and aquatic environments. However, we have a relatively poor understanding of the effects of ALAN in the marine realm. Here, we carried out a field experiment in the coral reef lagoon of Moorea, French Polynesia, to investigate the effects of long-term exposure (18–23 months) to chronic light pollution at night on the survival and growth of wild juvenile orange-fin anemonefish, Amphiprion chrysopterus. Long-term exposure to environmentally relevant underwater illuminance (mean: 4.3 lux), reduced survival (mean: 36%) and growth (mean: 44%) of juvenile anemonefish compared to that of juveniles exposed to natural moonlight underwater (mean: 0.03 lux). Our study carried out in an ecologically realistic situation in which the direct effects of artificial lighting on juvenile anemonefish are combined with the indirect consequences of artificial lighting on other species, such as their competitors, predators, and prey, revealed the negative impacts of ALAN on life-history traits. Not only are there immediate impacts of ALAN on mortality, but the decreased growth of surviving individuals may also have considerable fitness consequences later in life. Future studies examining the mechanisms behind these findings are vital to understand how organisms can cope and survive in nature under this globally increasing pollutant.

Extract

Figure 1. Photographs of (a) artificial light at night (ALAN) in Moorea, French Polynesia (photo credit: Jules Schligler) and (b) an orange-fin anemonefish, Amphiprion chrysopterus, in its host anemone Heteractis magnifica (photo credit: Fred Zuberer), and underwater light intensity measurements in (c) illuminance (lux) and (d) photosynthetic active radiation (PAR) in both treatments at each of the three sites. (Online version in colour.) https://royalsocietypublishing.org/doi/10.1098/rspb.2021.0454

In conclusion, combining the growing number of studies showing the negative impacts of ALAN in marine ecosystems with the projections of global population increases, especially along coastlines and the close association with levels of light pollution and population density, ALAN is already a risk to our marine ecosystems and will only exacerbate in the future. Marine-protected areas (MPAs) are not excluded from ALAN and due to the current lack of legislation, 20% of MPAs are already exposed to ALAN and 14.7% are exposed to increasing levels of light pollution [79], therefore mitigation measures should be of paramount importance. Mitigation measures and policy changes are urgently needed including maintaining and creating dark areas, only lighting part of the night and improving lighting technology in terms of directing light where it is needed, reducing light intensities, and changing spectra [80]. There is also growing concern regarding the combined interactions of multiple anthropogenic stressors, such as light and sound pollution [29,30] and the worldwide impact of these cumulative stressors needs to be better understood to help future management strategies [81].

https://royalsocietypublishing.org/doi/10.1098/rspb.2021.0454

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