The long-finned, tiger-striped lionfish may be one of the most stunning swimmers in the sea — but it’s also becoming one of the most problematic. Originally a native of the Indo-Pacific ocean region, this predatory tropical fish has already invaded the southern Atlantic coast of the U.S., the Gulf of Mexico, and parts of the Caribbean, sparking concerns about its potential impact on local ecosystems. And now, scientists believe it’s moving in on the Mediterranean as well.

In a new paper, published this week in the journal Marine Biodiversity Records, researchers describe what may be the beginning of a lionfish invasion off the coast of Cyprus in the Mediterranean Sea. The paper includes 24 reports of lionfish in the area from divers or fishers, each documented with a photograph, between 2014 and 2015.

Some of these have been sighted clustered together in small groups, which the usually solitary lionfish only does to mate. This behavior has experts worried that the fish are reproducing and spreading.

“This is the first time they’ve been seen congregating [in the area],” said Jason Hall-Spencer, a marine biology professor at Plymouth University and one of the paper’s authors, adding that lionfish tend to breed quickly and can produce hundreds of eggs at a time.

Invasive species of all kinds are a potential threat to any new ecosystem they settle in, since they have a tendency to upset the natural balance and compete with native species for food, space and other resources. Lionfish, for their part, are a big concern for marine biologists because they have a wide diet — “they’ll basically eat anything they can get into their mouths,” Hall-Spencer said — and have very few natural predators. This means they have the potential to eat their way through new ecosystems without anything to keep them in check. The lionfish is also known for its venomous spines and sharp sting — a defensive adaptation that can be extremely painful but is rarely fatal to humans.

Lionfish started turning up in Florida in the mid-1980s, likely after being released by aquarium owners. In the past few decades, they’ve crept up the east coast and spread into the Gulf of Mexico and the Caribbean, and are expected to continue spreading into the waters off South America as well.

They haven’t been much of a concern in the Mediterranean until recently, though. Experts have previously assumed the water there is too cold for these warm-water fish, according to Hall-Spencer. But over the past decade, he said, water temperatures in the region have slowly been creeping up — making the area more conducive to their survival.  

The scientists believe that a recent widening and deepening of the Suez Canal in Egypt, which connects the Red Sea and the Mediterranean Sea, has made the invasion possible.

“They used to have some very salty areas called the Bitter Lakes with high salinity that would kill off organisms as they tried to travel through from the Red Sea into the Mediterranean,” Hall-Spencer said. “But those Bitter Lakes have now been removed, and the salinity isn’t too high and allows the fish to pass through.”  

While the new sightings are a big concern for biologists, it’s not the end of the world yet, Hall-Spencer cautioned.

“If we act within the next couple of weeks — if the authorities … mobilize people to kill off these fish as quickly as possible — then they might be able to avert an ecological disaster,” he said.

In other parts of the world where lionfish have established themselves, such as in Florida, local authorities have launched campaigns to encourage people to catch and even eat them. While lionfish do have some venomous spines on their bodies, they are not poisonous overall and can be safely prepared for human consumption.  

Additionally, better biosecurity measures at the Suez Canal could help prevent more fish from getting in, Hall-Spencer added.

“It would be great if they had some locks, simple locks like you get on any normal canal,” he said. These would prevent water from flowing freely through the canal and would allow standing water to begin evaporating from the contained areas. As the seawater evaporates and leaves salt behind, the overall salt content of the remaining liquid water would rise and eventually become too high for fish to survive.

Preventing the invasion from getting out of hand is important not just for the sake of local fish, but for the people who depend on them, Hall-Spencer said.

“This is a brand new predator that doesn’t belong in the Mediterranean ecosystem,” he said. “Just like in the Caribbean, we think it could have massive effects on fisheries. So people’s livelihoods are at stake if this gets out of control.”