Artificial light on coastlines lures small fish to their destruction, coral reef study finds

Artificial light shining from coastlines around the world is acting as a “midnight refrigerator” full of tasty food, threatening young fish that may be attracted to it and then eaten by predators also attracted to the glow, according to a study .

Light pollution has long been proven to impair people’s ability to see the night sky and harm migrating birds, insects and other animals. But its impact on marine ecosystems has rarely been considered, said Jules Schligler, lead author of the study at the International Coral Ecosystem Research Center in Mo’orea, French Polynesia.

Nearly a quarter of the world’s coastline, excluding Antarctica, was artificially illuminated, according to a satellite survey conducted a decade ago, and it was probably more than that by now, Schligler said.

His study, which involved creating 12 coral test sites in the waters off Mo’orea and shining an underwater light on half of them, found that the artificially lit corals first attracted fish larvae and then the predators that ate them. .

“We found that the lighted coral attracted two to three times more fish compared to the naturally lit control site,” Schligler told the Guardian. “Coral with [artificial] light is a bad environment for larval fish because there are more predators, opportunistic fish that pass by and eat them.”

The findings, he said, meant that artificial light should be seen as “another threat to marine animal populations and coastal ecosystems”.

And while artificial light may appear to benefit predatory fish, Schligler said more research is needed. “It could be bad for their sleep, or they could be eating too much, we don’t know yet.”

The study did not examine why the larval fish were attracted to the artificial light, but there were two possibilities, he said. “Artificially lit coral can be like a midnight refrigerator full of delicious plankton that are also attracted to the light. The plankton attract the larvae, and then the larvae are chased by their predators.

“Or it could be the light itself and the prospect of food that attracts them. Either way, it makes everyone behave unnaturally.”

The findings, presented at the Society for Experimental Biology conference in Prague, focused on two species – the yellowtail dascyllus (Dascyllus flavicaudus) and blue-green chrome (Chromis viridis) – but could be applied more broadly, Schligler said.

“We can only extrapolate to a certain point, but our findings and other tests we did on crabs and shrimp generally show that marine animals are attracted to artificial light,” he said.

Oren Levy, head of the molecular marine ecology lab at Israel’s Bar-Ilan University, who was not part of the Schligler-led study, welcomed the Mo’orea research findings, saying they were consistent with his own work. .

Beyond the risk of being eaten, Levy said Mo’orea’s study showed that artificial light was negatively affecting the aging of the fish as well as their health. “It also damages reefs,” he added, pointing to a previous study that showed artificial light interfered with reproduction and caused corals to collapse.

On a more positive note, Levy and Schligler said that preventing light pollution, using timers and shades for example, was not difficult. “And we can start to consider light for things like marine protected areas,” Schligler said.