Light from harbors, ships, and offshore structures such as oil rigs may be disrupting the lives of marine worms, barnacles, and corals, preventing their wayfaring larvae from finding suitable habitats in which to settle down, according to a new study. Such light pollution could change the face of already stressed coastal marine ecosystems like coral reefs, which humans have come to rely on as sources of food, income, and even protection from incoming storms.

The findings could aid the conservation of some of the world’s most critical sea creatures, says urban ecologist Travis Longcore of the University of Southern California in Los Angeles, who was not involved with the work. “Light that we shine into places where other species live has consequences.”

To conduct the study, Thomas Davies, a community ecologist at the University of Exeter in the United Kingdom, and his team traveled to the Menai Strait, a narrow, shallow stretch of water that separates the mainland of northwest Wales from the island of Anglesey, an area that remains largely unaffected by light pollution. There, they immersed 36 plastic panels in wells on a floating raft anchored to the seabed for stability.

At night, they exposed some panels to light from cool, white LEDs that emitted either 19 lux or 30 lux—about the same brightness of streetlights. The control panels were exposed only to artificial light known as “sky glow,” ambient humanmade light scattered in the sky and reflected back to the sea surface by the atmosphere. Because artificial light in the Menai Strait is rare, Davies says, the sky glow in the region would likely have amounted to less light than what occurs during the full moon.

For 12 weeks the authors let seafaring invertebrate larvae—such as those belonging to marine worms, sea bristles, and squirts—accumulate on the panels and blossom into immobile, adult communities. When they retrieved the panels, the team counted up the number of individual organisms and examined how much surface area they had colonized.

The artificial lights reduced colonization of the panels by the sea squirt, Botrylloides leachi, and the sea bristle, Plumaluria setacea, filter feeders that dine on nutrients and plankton from the water column and keep coastal ecosystems healthy, the team reports online today in Biology Letters. But the marine worm Spirobranchus lamarcki was much more abundant on artificially lit panels than on control panels. Overall, the study found that the lights either encouraged or discouraged settlement in 39% of the taxa, or groups of species, living on the panels by the end of the experiment period. Artificial light may be negatively impacting marine ecosystems by driving away certain invertebrate species, like filter feeders, and attracting others, the team reports.

Many of the organisms that wound up living on the panels are known as fouling species—microorganisms, algae, and invertebrates that anchor to boat hulls, jetties, and aquaculture facilities and wreak havoc for both humans and local marine communities—so lighting up marinas and harbors may not be in our best interest. Barnacles, the most infamous of foulers, have been estimated to cost global economies upward of $303 million a year.

Much more information is needed before researchers can come up with optimal recommendations for light regulations, though. They would need to experiment with a whole range of exposures, as Davies’s study was on the high end of the artificial light scale that marine environments experience. And it’s not just about brightness; the cycle of exposure and the wavelengths artificial lights emit also likely play a role.

“The take-home message from this paper should be that we really need to go out and start quantifying what species are affected, how they’re affected, what the threshold of those effects are, and really get a handle on how much of a problem this is likely to be,” Davies says.

The good news is that once researchers know how lights affect the behavior of various species, designers will be able to configure LEDs to emit spectrums of light that may be less harmful to other organisms, but still provide humans with light where it is needed, according to Longcore. “Species are responding to cues sometimes that are orders of magnitude dimmer than what we can see, and that means that there’s a whole range of variation out there that we just don’t intuitively notice as humans,” he says. “To us it’s just dark, but there are many, many, many shades of dark.”