Artificial light is another type of human pollution that carries risks for wildlife. It may lure animals to unsafe places, cause them to flee from their normal habitat, or mess with their circadian rhythms. New research shows that even animals living below the ocean’s surface aren’t immune.

A study recently published in the journal Global Change Biology investigated how nighttime artificial light impacts coral reef communities. The researchers, from four different countries, note that reefs can be especially sensitive to human impacts due to their shallow, near-shore environments. They’re also diverse communities that serve as habitat to a wide variety of species that rely on the darkness for safety.

Andy Radford, senior author and professor from the University of Bristol, explains, “The night usually brings a veil of darkness that allows marine life to hide from nocturnal predators. But artificial light generated by human activities exposes coral reef inhabitants to unexpected danger.”

The study highlighted just how dangerous it may become when manmade light floods reefs that should be under the cover of darkness. The researchers used LED lights and infrared cameras in a Polynesian reef system to study how reef communities responded, compared to control sites without artificial light.

They found that shorter periods of artificial light exposure, an average of just three nights, showed little impact. However, longer term exposure averaging 25 nights led to more fish being out and about than there were before the experiment began. This included more nocturnal and diurnal predators, which feed on zooplankton, invertebrates, and small fish.

This difference in activity is not only bad for the prey, but also for the predators.

Dr. Emma Weschke, lead author from the University of Bristol’s School of Biological Sciences, explains, “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.”

However, the researchers did point to one silver lining. Because shorter-term exposure didn’t have these community impacts, it’s likely that managing the duration of artificial light exposure may stave off substantial changes to food chains and circadian rhythms.

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