About three years ago, a group of divers walked into a Nassau scuba shop and reported an odd sighting made while diving on a nearby shipwreck. They told shop owner Stuart Cove they’d seen a lionfish, a striped fish whose feathery, venomous spines radiate from its body like the costume on a Mardi Gras dancer.

Cove was dubious. Lionfish are native to the Indian and western Pacific oceans, half a world away from the Bahamas. But the divers were right: They returned, presenting a photograph of the fish on the wreck.

Soon, Cove and his crew were documenting lionfish on other wrecks and on coral reefs throughout the Bahamas. Initially, they saw pairs of them, then dozens. Before long, this curiosity became a serious pest.

The lionfish packs a nasty sting for swimmers who brush past its spines, and, at first, native Caribbean predators didn’t eat it, allowing its numbers to expand unchecked. The fish gobbles just about anything that fits in its mouth, including young grouper, a commercially important fish in the Bahamas.

But the lionfish, which likely got its start in the Caribbean after several were released from home aquariums, is hardly the most troublesome non-native species in the oceans. That distinction, according to a new report by Nature Conservancy scientists, goes to a number of particularly damaging invasives, including comb jellies, one species of green algae and the northern Pacific sea star. The report, published in the journal Frontiers in Ecology and the Environment, finds that invasives plague 84 percent of coastal regions, having been transported by four main “pathways”: shipping, fish farming, canal building and the aquarium trade.

“When we started looking at invasive species in all habitats, we recognized invasive species in marine environments were a threat, but we didn’t have information on a global scale,” says Jennifer Molnar, a conservation scientist with the Conservancy. Molnar’s team analyzed hundreds of archives and records and found information on more than 300 marine invasives, which the group compiled into a searchable database it hopes will assist in preventing future invasions.

Prevention is often the only viable option for combating marine invasives. The report finds that most of the invasives in the database would be difficult, if not impossible, to control.

To get a handle on the lionfish problem in the Bahamas, Conservancy collaborators, such as the College of the Bahamas and the Reef Environmental Education Foundation (REEF) of Key West, Florida, have been tracking the fish’s expansion — to the Turks and Caicos, Cuba, the Cayman Islands, Jamaica, and as far north as Florida and North Carolina. REEF is organizing rapid-response teams to act as soon as the fish turn up in a new location. “It may be too optimistic to say we can eliminate the fish [in the region],” says Lad Akins, a project director at REEF, “but we may be able to stay ahead of the game.”

—Madeline Bodin

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Nature picture credits: Photo © Stuart Cove/www.stuartcove.com (Collecting Lionfish)