Artificial Illumination Transforms Coral Reef Nightlife into a Predatory Playground

The research, published today in Global Change Biology, was carried out by an international group of scientists from the UK, France, French Polynesia, and Chile and is the first extensive experiment to examine the effects of light pollution on the nocturnal activities of coral reefs.

Lead author, Dr. Emma Weschke, from the University of Bristol’s School of Biological Sciences, stated: “When dusk arrives, coral reefs experience a significant change. The colorful fish visible during the day retreat to slumber among the corals while elusive nighttime species emerge from crevices in search of food.”

Senior author, Professor Andy Radford, also from Bristol, remarked: “Nighttime typically shrouds marine life in darkness, providing a refuge from nocturnal predators. However, artificial light created by human activities endangers coral reef inhabitants by exposing them to unforeseen threats.”

Employing specially designed underwater infrared night-vision cameras, the researchers were able to capture footage of the reef after dark without disrupting fish behavior, as fish are unable to perceive infrared light.

A greater variety of fish species were observed on artificially lit reefs at night compared to control locations devoid of artificial light. Further analysis indicated that these species were predatory fish, preying on zooplankton, small fish, and invertebrates.

Dr. Weschke noted: “Many of the species found on artificially illuminated reefs were not nocturnal, but rather those typically active during the daytime. Discovering that light pollution can lead fish to remain awake later than normal raises concerns, as sleep — similar to humans — is likely vital for energy restoration and maintaining fitness.”

Professor Radford elaborated: “Artificial light greatly facilitates predators in finding and capturing prey, diminishing their foraging efforts. Hence, we believe that higher numbers are being drawn to artificially illuminated coral reefs at night.”

The alterations in the nighttime activities on the reef were noted after an average exposure of 25 consecutive nights to artificial light. Just a few nights of exposure proved insufficient to trigger any significant changes in fish communities compared to controls.

“This is encouraging news as it indicates that there may be cost-effective solutions that can be swiftly implemented,” commented co-author Professor Steve Simpson, also from Bristol’s School of Biological Sciences. “Mitigating the impacts of artificial light could foster resilience in valuable coral reefs.”

Dr. Weschke added: “In contrast to greenhouse gases and plastics, artificial light is a pollutant that does not leave any residue when turned off.”

“Restricting artificial illumination in both its intensity and duration, focusing it on necessary applications, and minimizing aesthetic use, will help restore naturally dark evenings that marine ecosystems have evolved alongside.”

The research was undertaken by scholars from the University of Bristol, UK, Centre de Recherches Insulaires et Observatoire de l’Environnement (CRIOBE), French Polynesia, and Pontificia Universidad Católica de Chile.