A poisonous tropical fish with the potential to kill humans may be spreading in the Mediterranean, alarming conservationists who fear the creature could decimate other species in the ecosystem.

The predatory, highly invasive lionfish - armed with poisonous barbs and a painful sting that can even prove deadly to humans - has been spotted in waters around Turkey and Cyprus in the eastern Mediterranean, warns the International Union for the Conservation of Nature (IUCN).

Maria del Mar Otero of the IUCN said: "The fish is spreading - and that's a cause for concern."

The species, also known as the devil firefish, is native to the South Pacific and Indian Ocean. It mysteriously reached the Atlantic some decades ago, where it has been wreaking havoc on marine ecosystems there - including in the Caribbean.

Environmentalists fear that the arrival in the eastern Mediterranean of the fish - whose stings can cause extreme pain, vomiting and respiratory paralysis - could have knock-on effects on the rest of the marine environment.

Reverberating impacts

Despite their conspicuous colors and slow movements, even sharks won't go near lionfish - meaning they have free rein to feed on and wipe out other species, including those that would normally keep algae under control.

This can attract the arrival of new invasive species, due to weakening of the local fauna and flora, said Carlos Jimenez, a marine biologist at the Cyprus Institute.

For this reason, lionfish "could have a heavy negative impact on the ecosystems as well as on local economies" in the Mediterranean said Jimenez.

The arrival of lionfish could impact local economies in the Mediterranean, as they often depend on the sea

Rise of the lionfish

The first sightings of the fish in the Mediterranean were near Israel in 1991. More recently, they have been seen in Lebanese and Tunisian waters, according to the IUCN.

The fish could have been introduced by aquarium enthusiasts who let them loose, experts say - or via the Suez Canal from the Red Sea, which can act as a channel for nonnative species.

According to the National Oceanic and Atmospheric Administration (NOAA), a US government agency, lionfish are a major threat in Atlantic reefs, and are now established along the southeast coast of the United States, the Caribbean, and in parts of the Gulf of Mexico.

Experts are still baffled as to the how the fish reached the Atlantic - but like in the Mediterranean, they believe humans lent a helping hand, and speculate that people have been dumping unwanted lionfish from home aquariums into the ocean for up to 25 years.

Cargo ships' ballast waters are also an ideal hiding place for invasive species.

The NOAA added that colder water temperatures constitute another environmental factor that controls the species' distribution on a large scale. As ocean waters warm as a result of climate change, lionfish and other invasive species may expand their range and begin affecting presently untouched ecosystems, the agency said.

Lionfish probably reached the Atlantic after being dumped as pets

Overarching problem of overfishing

But when it comes to the lionfish's spread in the Mediterranean, experts believe climate change isn't as significant as factors like overfishing.

Carl Gustaf Lundin, director of IUCN's Global Marine and Polar Program, told DW: "The Mediterranean has been severely overfished for the last 2,000 years - so climate change is the last in a long row of very bad things we have done in that sea."

Ken Collins, a marine scientist and senior research fellow at the University of Southampton, told DW that the presence of predatory grouper "controls the lionfish population in the Indian Ocean and the Australian Pacific."

But grouper "has long since dried up in the Mediterranean and the Caribbean, as they are easy to catch," Collins said.

Cumulative ocean impacts

Lundin said another factor is how marine ecosystems were already vulnerable when lionfish arrived: "Sometimes the ecosystem is disturbed, so it's not as robust as it could be."

"In the Caribbean, there should be 90 percent corals, but it's 14 percent coral now, and in some places it's even 4 percent - so that shows the ecosystem is really sick there," Lundin said.

Although the Mediterranean suffers from overfishing, catching lionfish could be beneficial

NOAA researchers warned that invasive lionfish populations will continue to grow, and cannot be eliminated using conventional methods. Marine invaders are nearly impossible to eradicate once established.

Eating for ecology

In places like Cuba, Colombia and the Bahamas, governments have encouraged their populations to start eating the fish to keep down numbers.

Cuba now holds an annual fishing tournament for the species. Restaurants have begun serving its juicy white flesh, which is enjoyed as a delicacy in Japan.

Lundin thinks encouraging people to eat lionfish around the Mediterranean would also be a good move.

"Either we do eradication, or we do control - but we can forget about eradication," he said.

In light of how overfished the Mediterranean already is, encouraging more fishing generally is not a good idea, Lundin said. "But in this case, we can make an exception."