The highly venomous lionfish has been seen off the coast of Italy for the first time, confirming fears the invasive species has expanded its range in the Mediterranean Sea. It has already devastated Atlantic ecosystems.
Image: picture-alliance/blickwinkel/A. Trutnau
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Threat beneath the waves: invasive marine species
The extravagant lionfish, the tiny zebra mussel, the common trout: these invasive aquatic species may look cool - but they pose a serious risk to native ecosystems around the world.
Image: picture-alliance/blickwinkel/A. Trutnau
Armed invader
With 18 poisonous barbs, the invasive lionfish wreaks havoc on marine ecosystems where it's been introduced - in the Atlantic, in the Caribbean and now, in the Mediterranean Sea. Its painful sting isn't necessarily deadly, but it's enough to scare off potential predators. In places like Florida, Cuba, Colombia and the Bahamas, governments have encouraged people to start killing or eating the fish.
Image: CC BY 3.0/Alexander Vasenin
Beautiful threat
The sea walnut, a kind of jellyfish, is originally from the east coast of the Americas. In the early 1980s, it turned up in the Black Sea and then the Caspian Sea, transported in the ballast water of cargo ships. It has since spread to the Mediterranean, North and Baltic seas. At 12 centimeters (5 inches) in length, it competes with fish for food and has led to the collapse of fisheries.
This common seaweed is one of two algae on the list of the world's 100 worst invasive species, as compiled by the IUCN. Widely used in home aquariums, the invasive plant was accidentally introduced into the Mediterranean in wastewater from the Oceanographic Museum at Monaco. It has spread over more than 13,000 hectares of seabed, preventing the growth of native seaweeds and other marine life.
Image: picture-alliance/OKAPIA KG, Germany
Tiny terror
The zebra mussel is a common sight on the shores of North America's Great Lakes - but that wasn't always the case. Originally from the Caspian and Black seas, the mollusk spread through canals in the 1800s and 1900s to the Baltic Sea, and by the 1990s to lakes and waterways in Canada and the US. It has become a nuisance, clogging water intake pipes and competing with local fish for plankton.
Image: picture alliance/blickwinkel/A. Hartl
World domination
A very well-known species, the rainbow trout is now found around the world, having been introduced for sport fishing and commercial aquaculture. Its home is the West Coast of North America and cold-water tributaries, but it can now be found on every continent - where it out-competes and preys on native fish populations.
Image: picture alliance/Arco Images
Reef risk
This barnacle is native to Caribbean waters, but was introduced - likely by cargo ships - to the Pacific in the 1970s. It reached Hawaii in the mid 1990s, and has become one of the most abundant organisms in harbors and bays throughout the Hawaiian Islands, according to Reef Resilience. The barnacle is seen as a threat to coral reefs, as they can prey on the soft inner tissues of coral polyps.
Image: Flickr/James St. John
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The lionfish, an extravagantly frilled trespasser from the South Pacific and Indian Ocean, has been slowly spreading through the relatively warm waters of the Mediterranean ever since it was first spotted off the coast of Israel in 1991.
Over the last two decades the poisonous threat has been found in the waters near Turkey, Cyprus and Lebanon and, in 2015, off Tunisia, according to the International Union for the Conservation of Nature (IUCN).
But now, just months before the summer beach season, the lionfish has been sighted further west, turning up in the Vendicari marine reserve in southeastern Sicily, Italy's Institute for Environmental Protection and Research reported earlier this week.
Stinging spines
The lionfish, also known as zebrafish or devil firefish due to its striped pattern and bright coloring, can grow up to 40 centimeters (15 inches) in length. It's one of the ocean's most venomous creatures, sporting 18 sharp spines that can easily penetrate human skin.
While the venom isn't usually deadly, being stuck by a lionfish can leave behind a very painful sting that can last anywhere from a few hours to a few days.
"The lionfish observed at Vendicari represented the first known occurrence of this species in Italian waters, and its observation confirms a trend of rapid expansion through the Mediterranean Sea," researchers wrote in the scientific journal BioInvasions Records.
Combating an invasive species
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'Urgent need to take action'
While researchers said the widespread presence of the lionfish in European waters is "still below the threshold of a true invasion," they stressed there was an "urgent need to take action and to promote control measures."
In the absence of natural predators, the invasive fish can easily reach very high population densities and cause significant disruption to local ecosystems and wildlife.
Introduced deliberately by humans or accidentally via the ballast waters of cargo ships, or - as was likely the case in the Mediterranean - via the Suez Canal, the lionfish has become one of the world's top conservation concerns over the last quarter century.
The lionfish has become a major threat to native species in the Caribbean Sea and the West Atlantic around Florida. Conservationists have been encouraging anglers and divers to hunt and kill lionfish to stop their spread.
