This article originally appeared in Hakai Magazine.

In several quiet rooms in a marine lab in southwest France, dozens of Pacific oysters sit in glass tanks, quietly living their oyster lives. Each morning, the lights come up slowly, carefully mimicking the rising sun, but at night the test groups’ rooms never fully darken. The dim glow simulates the light pollution that plagues many marine species—even in natural habitats.

The results of the experiment, which were recently published, found that artificial light at night can disrupt oyster behavior and alter the activity of important genes that keep the animals’ internal clocks ticking.

Damien Tran, a marine scientist at the Paris-based French National Centre for Scientific Research and one of the study’s authors, was surprised that even the lowest level of nighttime light that the team tested—“below the intensity of the full moon,” he says—was enough to throw off the oysters’ circadian rhythm.

It’s especially remarkable, Tran says, when you remember that oysters don’t have eyes—at least not in the conventional sense.

How oysters see is a bit of a mystery. While other bivalves, such as scallops, have eyelike organs, oysters may use specialized cells on their skin to detect light, though scientists have yet to definitively identify the cells or figure out exactly how they might work.

[Read: Scallops have eyes, and each one builds a beautiful living mirror]

In the recent study, Tran and his colleagues put four tanks of oysters in different rooms and exposed each to a different intensity of artificial light at night. The researchers compared these oysters’ behavior with that of their counterparts in a control tank that experienced complete nighttime darkness.

Tran’s colleague and co-author, the marine scientist Laura Payton, explains that shell movement is really the only oyster behavior that can be observed. The team fitted half the oysters in each tank with electrodes to determine when the animals opened their shells—something oysters do to feed, breathe, and mate. In the control tank, oysters were most active in the middle of the day and started to close when the lights went out.

But exposure to artificial light at night caused the oysters in the other four tanks to stay open at inappropriate times, with activity peaking in the early evening. And while oysters have certain genes that typically turn “on” during the day and others that turn on at night, exposure to nighttime light virtually eliminated the difference. For example, the oyster equivalent of a mammal gene that helps make melatonin is usually expressed more at night, but the researchers observed that the gene stayed highly active during the day, disrupting the natural circadian rhythm.

[Read: The dark side of light]

In human terms, that’s called insomnia. In oysters, as Payton explains, this response could negatively affect their health, possibly making the animals more vulnerable to disease over the long term. She concedes, though, that many of the specific consequences have yet to be studied.

If oyster populations do suffer, so would the ecology and economy of many regions worldwide, where oysters filter water, protect shorelines from storms, and, as a commercially grown species, provide food and jobs to communities.

Emily Fobert, a marine ecologist at the University of Melbourne, in Australia, who was not involved in the research, says the results are compelling. But she critiqued the researchers’ choice to expose just one tank of oysters to each level of artificial light. That means there’s a chance that the study results were caused by something else in the tank, rather than the light alone, she says. Fobert doesn’t question that the changes in oyster behavior and gene expression were due to the artificial light, but having multiple tanks per light level would have made the study more robust, she says.

Nevertheless, artificial light at night is a growing concern for many marine species. Oysters in particular need our help, Payton says, because they can’t quickly run away when their environment is disturbed.

Technologically, Fobert says, it’s completely in our power to improve conditions for the health and well-being of marine species that are affected by light pollution. “We have huge opportunities to get it right.”

France is broadly supportive of stopping girls wearing the robe, but many Muslim women are unhappy.