Artificial light from coastlines worldwide acts like “a midnight fridge” full of snacks, drawing in young fish who are then eaten by predators also attracted to the brightness, according to a study.
Light pollution is known to affect night sky visibility and harm migrating birds, insects, and other animals, but its impact on marine ecosystems has been less studied, said Jules Schligler, lead author of the study at the international coral ecosystem research centre in Mo’orea, French Polynesia.
A satellite study from a decade ago showed that nearly a quarter of the world’s coastline, excluding Antarctica, was artificially lit, and this figure has likely increased, Schligler said.
Schligler’s study involved creating 12 coral test sites in the waters off Mo’orea and shining an underwater light on half of them. The artificially lit corals first attracted fish larvae and then predators that ate them.
“We found that the coral with the light attracted two to three times more fish compared to the naturally lit control site,” Schligler said. “The coral with the [artificial] light is a bad environment for the larval fish because there are more predators, opportunistic fish passing by, that ate them.”
These findings suggest that artificial light should be viewed as “another threat to marine animal populations and coastal ecosystems.”
While artificial light may seem to benefit predator fish, Schligler emphasised the need for further research. The study did not investigate why larval fish are drawn to artificial light, but Schligler suggested two possible explanations.
“The artificially lit coral could be like a midnight fridge full of tasty plankton that are drawn to the light too. The plankton attract the larvae, and then the larvae are followed by their predators.
“Or it might be both the light itself and the prospect of food that attract them. Either way it makes them all behave unnaturally.”
Presented at the Society for Experimental Biology conference in Prague, the study focused on two species—yellowtail dascyllus (Dascyllus flavicaudus) and blue-green chromis (Chromis viridis)—but Schligler believes the findings could be more broadly applicable.
“We can only extrapolate to a certain point but our findings, and other tests we did on crab and shrimp, generally indicate that marine animals are attracted to artificial light,” he said.
Oren Levy, head of the laboratory for molecular marine ecology at Israel’s Bar-Ilan University, who was not involved in the study, praised the Mo’orea research, noting its consistency with his own findings.
Beyond the immediate risk of predation, Levy noted that artificial light negatively impacts fish aging and health.
“It harms the reefs too,” he added, pointing to a previous study that showed artificial light interfered with reproduction and caused corals to collapse.
Encouragingly, both Levy and Schligler highlighted that mitigating light pollution is relatively straightforward, using methods such as timers and shades.
“And we can start to take light into account for things like marine protected areas,” said Schligler.
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