The invasive lionfish that crowds coral reefs and preys on native fish in the Atlantic's shallower waters -- especially the Florida Keys -- is such a problem that divers in Florida and the Caribbean are encouraged to capture and eat them whenever they can.
Lionfish, which have venomous spines, are a well-documented problem in Atlantic coral reefs, where the foot-long, 1-pound invaders from the tropical parts of the Pacific and Indian oceans live without predators and eat other fish voraciously.
Now what's slowly coming into view is how deep into the ocean their invasion has spread.
Researchers and wildlife officials worry that lionfish may undo conservation efforts aimed at rebuilding populations of native predators such as groupers and snappers. Lionfish gorge on the young of those species, as well as their prey.
"They can eat pretty much anything that fits inside their mouths," Oregon State University lionfish expert Stephanie Green said.
Divers are encouraged to capture any lionfish they encounter to protect reefs and native marine life already burdened by pollution, over-fishing and the effects of climate change. And last month, the Florida Fish and Wildlife Conservation Commission waived the recreational license requirement for divers harvesting lionfish and excluded them from bag limits, allowing people to catch as many as they can.
But recreational divers max out around 130 feet deep. Researchers and wildlife officials rarely have the means to venture deeper than that, but they've realized the lionfish they can't see may be their biggest concern.
As Green discovered on a recent expedition aboard a submersible, there's little to disturb a lionfish living on a wreck 250 feet deep into the Atlantic. There are no predators and no divers.
Last month, Seattle-based OceanGate Inc. offered scientists and wildlife officials a close-up look at deep-water lionfish in dives aboard a submersible named Antipodes, which left out of Broward County. In strong currents that might have tangled a tether connecting a remotely operated robot to a vessel at the surface, the Antipodes sank and rose as smoothly as an elevator. Maneuvered by a joystick, it crawled over the sand at a walking pace.
Green and other researchers who took the dives surfaced believing they had seen the frontier in their fight against lionfish. The next problem will be routinely making similar dives to study and perhaps capture lionfish.
They would seem to have a lot of water to cover -- the deepest confirmed sighting of a lionfish was at 1,000 feet in the Bahamas.
"We are capable of doing a good job of controlling lionfish at diveable depths, in shallower areas. Divers and spearfishers can go in and remove the fish. But the lionfish are abundant in large numbers at these deeper habitats, and that's really where the next frontier of this battle is going to be, in those deep water areas," Green said.
Lionfish in the Atlantic Ocean have similarities to the Burmese python, the large, ravenous snake that researchers say is decimating native mammal populations in Florida's Everglades. Both are fast-breeding invasive species likely introduced through the pet trade, with no natural predators to keep their numbers in check.
"We're going to have to figure out how we're going to get below the diver depths," said Dan Ellinor, a biological administrator with the FWC's marine fisheries division.
"The other problem is there's not a commercial market per se," he added. "It's very small, very minute, it's in the Keys, it's beyond the reef in about 200 feet of water and it's bycatch out of traps, lobster traps."
Officials have concluded that if you can't beat lionfish, you can at least eat them, even though commercial supplies and the market for them remain very small.
Associated Press writers Ben Fox and David McFadden contributed to this report.