Indo-Pacific lionfish, an invasive carnivore equipped with venomous spines, are spreading—and eating their way—through the fishes of the Caribbean Sea. In an effort to stop, or at least slow down, these fearless invaders, the National Science Foundation has awarded a 3-year, $700,000 grant to scientists at Oregon State University (OSU), Corvallis. The lionfish are normally found in Pacific Ocean waters. But since the 1990s, they've been spotted from Florida to Rhode Island, and as far south as Colombia, and are now wreaking havoc among the fishes of Caribbean coral reefs—adding yet another woe to those already facing the reefs.
"We want to understand why lionfish are so successful," in their new habitats, says Mark Hixon, a marine biologist at OSU and leader of the newly funded research effort. Rare in their native waters, the lavishly striped and decorated fish (Pterois volitans) are booming on the reefs around the Bahama Islands, Hixon's previous work shows. In a controlled experiment in 2005, his team recorded the lionfish's voracious appetite. A single one can reduce the number of other fishes by 79% in as few as 5 weeks. The researchers witnessed colorful cardinalfish, parrotfish, damselfish all going down the lionfish's gullet. One consumed 20 small fish in 30 minutes. "It seems that the native fish don't perceive lionfish as fish," perhaps because of the predator's markings, Hixon says. "They swim right up to it," only to end up being swallowed whole.
Many of the small reef fish are herbivores and help keep seaweed in check; without them, Hixon and others predict that seaweed may grow rampantly, overwhelming the reefs' ecosystem.
Hixon's new study will compare lionfish populations in the Pacific and Atlantic oceans to try to sort out why they are rare at home, but thriving in foreign seas. "Something, a parasite, predator, or disease," is limiting them in the Pacific, says Hixon. If the researchers can discover what that is, they hope to find—and foster—a similar lionfish attacker in the Atlantic. Native groupers in the Bahamas might prey on lionfish, but because groupers have been overfished, they are unlikely to significantly reduce the invaders. Plus, in experiments, Hixon has found that neither groupers nor sharks are particularly keen to eat the lionfish. "They don't look like their conventional prey," and the groupers and shark don't seem to enjoy the venomous spike that comes with the meal.
Hixon has larger hopes for humans as consumers of lionfish. The fish are fairly easy to catch, are tasty, and could even carry a green label. "They could be advertised as a conservation dish," he says, noting that there is a lionfish cookbook in the works.
Lionfish are typically found at depths of at least 25 meters and in tropical, warm waters about 25°C. They can grow up to 48 centimeters long and are notable for their fan of feathery spines. Any diver that inadvertently touches one gets a jolt of venom that can cause severe pain and respiratory problems; the stings are rarely fatal. Lionfish-eradication efforts are under way in Florida and Caribbean waters, although researchers doubt these will do more than control the invaders' numbers.
No one knows how lionfish made their way from the Pacific to the Atlantic, although there are many theories. Lionfish are popular with tropical fish enthusiasts, and a private owner may have released them into the wild. Or, they may have been transported in a ship's ballast waters. There's even the possibility that Hurricane Andrew sucked them out of outdoor arenas, then dumped them off the Florida coast.