Why Are Lionfish Invasive in the Atlantic? Spread and Impact

How did lionfish get into the Atlantic?

The red lionfish is native to the western and central Pacific, and its close relative the devil firefish lives in the Indian Ocean and Red Sea. Neither belongs in the Atlantic. The first lionfish recorded in the western Atlantic was seen off Dania Beach, south Florida, in 1985.

The most likely source is the aquarium trade. Lionfish are among the most popular marine aquarium fish, and they grow large and eat smaller tankmates, so some owners released unwanted fish into the sea. Genetic studies show that Atlantic lionfish have low genetic diversity compared with Pacific populations, which means the invasion started from only a small number of fish. About 93% of the invaders are red lionfish and the rest are devil firefish.

A popular story blames Hurricane Andrew, which damaged a seaside aquarium in 1992 and let six lionfish escape into Biscayne Bay. That release did happen, but lionfish were already being seen off Florida seven years earlier, so the storm cannot explain the invasion on its own.

How fast did lionfish spread?

For about 15 years lionfish were reported only occasionally. Then the population exploded, producing what researchers have described as a marine fish invasion of unparalleled speed.

The larvae did most of the traveling. Lionfish eggs and larvae drift in the plankton for around a month, so ocean currents such as the Gulf Stream and the Caribbean Current carried young fish from island to island. Ships’ ballast water may also have moved a few.

Why are lionfish so successful?

Several traits together make lionfish exceptional invaders.

• Fast breeding. In warm water a female can spawn every few days all year round, releasing an estimated 2 million eggs a year. Young fish can breed before they are a year old.
• Naive prey. Atlantic reef fish never evolved alongside lionfish. Their slow, hovering approach and spread fins do not look like a typical predator, so small fish often fail to flee until it is too late.
• Few predators. The venomous spines deter most predators, and native fish rarely recognize lionfish as food. Large groupers that can eat them have been overfished in much of the region.
• A broad diet. Lionfish eat dozens of species of small fish, shrimps and crabs, so they can thrive almost anywhere they settle.
• Many habitats. They live on coral and rocky reefs, wrecks, seagrass beds and mangroves, tolerate brackish water in estuaries, and occupy deep reefs well below 100 m (330 ft).
• Few parasites. Atlantic lionfish carry very few parasites compared with many native reef fish, which may help them grow and breed faster.

Their spread is limited mainly by cold water. Lionfish cannot survive water colder than about 10 °C (50 °F) for long, which is why adults are established only as far north as about Cape Hatteras, North Carolina.

What damage do lionfish do to reefs?

Lionfish harm reefs mainly by eating huge numbers of young fish. In a well-known experiment in the Bahamas, published in 2008, a single lionfish on a small patch reef reduced the number of young native fish settling there by 79% in just five weeks.

A larger study on reefs off New Providence Island, Bahamas, published in 2012, found that lionfish numbers rose rapidly between 2004 and 2010, until they made up nearly 40% of the predator biomass on the reefs. Over just two years, the total biomass of the 42 native fish species they were eating fell by 65%.

The prey include young parrotfish and other grazers that keep seaweed from smothering corals, as well as the juveniles of snappers and groupers that support local fisheries. Lionfish also compete with native predators for food. Scientists worry that the loss of grazing fish adds to the problems facing reefs already hit by bleaching, disease and pollution, described in What is happening to Florida’s coral reefs?

Lionfish in the Mediterranean

A second invasion is now under way in Europe. The devil firefish (Pterois miles) has entered the Mediterranean Sea from the Red Sea through the Suez Canal, joining more than 100 other fish species that have made the same journey.

A single devil firefish was recorded off Israel in 1991, but the real invasion began around 2012, when lionfish appeared off Lebanon. They then spread quickly along the coasts of Cyprus, Turkey and Greece and reached the central Mediterranean, including Sicily, Malta and Tunisia. Warmer sea temperatures are thought to be helping them, and scientists expect them to keep moving west and north.

Can the lionfish invasion be stopped?

Complete eradication from the Atlantic is considered impossible. Lionfish now live across millions of square kilometers of ocean, from shallow lagoons to deep reefs far beyond the reach of divers, and new larvae keep arriving on the currents.

Instead, managers try to keep numbers low where it matters most. Marine sanctuaries and parks run regular removals with trained divers, volunteer groups hold organized removal events, and wildlife agencies in Florida and elsewhere encourage the public to report sightings. Studies show that regular removals can cut lionfish numbers on shallow reefs and help native fish recover locally.

Another approach turns the invader into seafood. Since 2010 NOAA has promoted eating lionfish, whose flesh contains no venom, and lionfish now appear on restaurant menus in Florida and the Caribbean. To understand why handling them takes care, see Are lionfish venomous?