New research utilising innovative underwater infrared cameras has revealed that artificial light can disturb sleeping fish and lure in predators, thereby altering the dynamics of nighttime coral reef communities.
The findings, published in Global Change Biology, stem from a collaborative effort by an international team of scientists from the UK, France, French Polynesia, and Chile. This study marks the first large-scale examination of how light pollution affects the nocturnal activities of coral reefs.
Dr. Emma Weschke, the lead author from the University of Bristol’s School of Biological Sciences, explained, “When the sun sets, coral reefs undergo a dramatic transformation. The vibrant fish we see in the day retreat to sleep among the corals and elusive nocturnal species emerge from caves and cervices in pursuit of prey.”
Professor Andy Radford, the senior author also from Bristol, noted, “Typically, nightfall provides a cover of darkness that helps marine creatures evade nocturnal predators. However, artificial lighting from human sources puts coral reef residents at an unexpected risk.”
By employing specially designed underwater infrared night-vision cameras, the researchers were able to observe the reef at night without disturbing the fish, as they are unable to perceive infrared light.
The study found a greater diversity of fish species present on reefs illuminated by artificial light at night compared to control sites without such lighting. Further analysis indicated that these species were primarily predatory fish, preying on zooplankton, small fish, and invertebrates.
Dr. Weschke expressed concern, stating, “Many of the species detected on artificially lit reefs were not nocturnal fish, but those that are only usually active during the day. Finding that light pollution can cause fish to stay awake later than usual is concerning because sleep—like for us—is likely essential for regenerating energy and maintaining fitness.”
Professor Radford noted that artificial light significantly aids predators in finding and catching their prey, which lessens their need to search for food. This is why we believe that more creatures are drawn to coral reefs that are lit up at night.
The changes in the reef’s nightlife were recorded after an average of 25 nights of exposure to artificial light. A few nights of exposure were insufficient to show any significant differences in fish populations compared to control areas.
“This is positive news as it suggests that there could be low-cost solutions that are quick to implement,” said co-author Professor Steve Simpson, also of Bristol’s School of Biological Sciences. “Reducing the impacts of artificial light could help build resilience on valuable coral reefs.”
Dr. Weschke added, “Unlike greenhouse gases and plastics, artificial light is a pollutant that doesn’t leave a residue when switched off.
“Limiting artificial light in both its intensity and duration, prioritizing it for essential needs and reducing aesthetic use, will help reestablish naturally dark nights that marine ecosystems evolved with.”
