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"Nothing like this has been seen before in these waters," said Pam Schofield, a research fishery biologist with the USGS Southeast Ecological Science Center in Gainesville, Florida. "We've observed sightings of numerous nonnative species, but the extent and speed with which lionfishes have spread has been unprecedented; lionfishes pretty much blanketed the Caribbean in three short years."

More than 30 species of nonnative marine fishes have been sighted off the coast of Florida alone (see Field Guide to the Nonindigenous Marine Fishes of Florida), but none of these have demonstrated the ability to survive, reproduce, and spread successfully until now. Originally from tropical waters of the Indian and western Pacific Oceans, two species of lionfish, Pterois volitans and Pterois miles, have been documented spreading along the Atlantic coast of the United States and throughout the Caribbean. Their populations in the region are now self-sustaining. 

It is not yet clear exactly how the new invasive species will affect coral reef ecosystems in this part of the world. Foremost on the minds of both citizens and scientists is the lionfishes' predatory behavior, which may negatively impact native species in the newly invaded reef ecosystems. Generalist species with a broad diet, they have already been observed preying on and competing with a wide range of native species. 

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Invasive lionfishes were first reported off Florida's Atlantic coast in the mid-1980s but did not become numerous in the region until 2000. Since then, the lionfish population has rapidly spread north along the Atlantic coast and south throughout most of the Caribbean. The spreading population is now working its way around the Gulf of Mexico. 

Schofield spent years compiling and verifying lionfish sightings, reaching out to local experts such as biologists, museum curators, natural-resource managers, divemasters, and citizens' groups to collect detailed records of specimen collections and sightings throughout the region. The records were compiled in the USGS Nonindigenous Aquatic Species database and used to map the fishes' spread.

No one knows for sure exactly how the predecessors of the current population first made it into the Atlantic and Caribbean. It is unlikely, based on their biology, that lionfishes could have arrived as many marine invaders do, by hitching a ride in the ballast water of commercial ships. 

Lionfishes have several distinct biological characteristics that may have helped them become established—their decorative spines, valued in the ornamental pet trade for their aesthetic appeal, are venomous to any would-be predators. Their broad diet, high reproductive potential, and ability to survive at a wide range of depths are other factors that may have helped them become established.

Schofield believes the invasion serves as a warning of the dangers posed by introductions of nonnative fishes into an ecosystem. Some scientists even view invasive species as a form of biological pollution, notes Schofield, who is concerned about the possibility of other nonnative fishes becoming established. One thing is clear—as the first exotic fish species to actively breed and expand into Caribbean reefs, the lionfish illustrates the relatively short time required by nonnative marine fishes, once established, to spread. 

"This invasion may constitute a harbinger of the emerging threat of nonnative marine fishes to coastal systems," Schofield said.

In the Florida Keys, Schofield and her team are working closely with partners from the National Oceanic and Atmospheric Administration (NOAA) in Beaufort, North Carolina, and Reef Environmental Education Foundation (REEF) in Key Largo, Florida, to analyze lionfish diets, an important first step in understanding their impact on reef ecosystems.

Eradication of lionfishes is probably not possible, admits Schofield. Yet, local control efforts may be able to keep the population tamped down, releasing pressure on the native ecosystem. Many Caribbean countries, such as Bermuda and the Cayman Islands, have begun lionfish control programs. In the United States, REEF held a series of lionfish derbies in the Florida Keys that resulted in more than 600 lionfishes being removed from the Florida Keys National Marine Sanctuary.

Schofield's most recent paper, "Update on geographic spread of invasive lionfishes (Pterois volitans [Linnaeus, 1758] and P. miles [Bennett, 1828]) in the western North Atlantic Ocean, Caribbean Sea and Gulf of Mexico," was published in December 2010 in volume 5, supplement 1 of the journal Aquatic Invasions; it updates a September 2009 article published in the same journal, volume 4 issue 3.

For more information on lionfishes, visit the USGS Nonindigenous Aquatic Species lionfish page.