LIANE HANSEN, host:

In 1992, Hurricane Andrew smashed an aquarium tank in Florida. About a half-dozen spiny, venomous lionfish washed into the Atlantic Ocean. Lionfish are native to the Indian and Pacific Oceans, but in the past few years they've spread up the eastern seaboard and throughout the Caribbean. The Bahamas have been hit the hardest.

Ann Dornfeld has the story from the Exuma Islands.

ANN DORNFELD: People come to the Exumas to kayak between tiny, uninhabited islands and dive in the shallow, turquoise water.

(Soundbite of splash)

DORNFELD: Above the water, the landscape looks like pristine tropical paradise. But the same is not true beneath the waves. Oregon State University zoology professor, Mark Hixon, has studied reef fish here for almost two decades.

Professor MARK HIXON (Zoology, Oregon State University): In 2005, the first lionfish showed up, and we didn't pay much attention to it. The next year, we saw a few more. And then in 2007 there was a population explosion. There were so many lionfish around that they were eating the fish that we were studying, and we had to start studying the lionfish. There was nothing else to do.

DORNFELD: They're hard to miss with their red and white stripes and a tall row of venomous spines down their backs. The fan-like fins look like a lion's mane. And like a lion, they're ferocious predators. Last year, Hixon co-authored a study with Mark Albins that showed a lionfish can kill three-quarters of a reef's fish population in just five weeks.

Prof. HIXON: This year we're going to see if that's gotten worse — because the number of lionfish has definitely increased in the intervening year.

(Soundbite of scuba gear)

DORNFELD: We pull on scuba gear and descend to the coral reefs.

(Soundbite of splashing)

DORNFELD: Hixon shines a light under every ledge, looking for lionfish and the fish they like to eat. After a few minutes, he waves his light frantically under an overhang. A lionfish the size of a football fans the water with its huge, quilled fins. These days, the only thing unusual about spotting a lionfish in the Bahamas is seeing just one of them.

Back on the boat, Hixon is upbeat. Last year, his team pulled more than a dozen lionfish off this reef.

Prof. HIXON: And this year, there's just one. And so what that tells us is that our removals took and lasted a whole year.

DORNFELD: But Hixon says divers can only catch so many. So he's also studying native lionfish in the Pacific Ocean to understand what keeps their populations in check. Parasites could be one limiting factor.

Zoologist Paul Sikkel peers through a microscope at the gills of one of the lionfish Hixon's team has just caught.

Mr. PAUL SIKKEL (Zoologist): Wow. Just so clean. There's nothing in there. Have a look. A local fish, you'd see a bunch of really small worms on those red gill filaments. And they squirm, so it's easy to pick them out. But there's nothing on there.

DORNFELD: Sikkel says native fish are crawling with parasites - these lionfish aren't - and that might be one secret to the invasion.

Mr. SIKKEL: If you consider parasites as sort of a tax that fish have to pay, a lot of their energy gets diverted into parasites, and so a fish that doesn't have those can devote more of its energy to its own growth and reproduction.

DORNFELD: Until marine predators or parasites learn to feed on lionfish, the best hope for slowing the spread may be humans. They're a delicacy in Asia, but not in the Bahamas, given the painful sting their spines can inflict. A few restaurants serve lionfish now, but there's an effort to teach Bahamians to catch and cook them.

Lakeshia Anderson with the Bahamas Department of Fisheries says their livelihoods depend on slowing the invasion.

Ms. LAKESHIA ANDERSON (Bahamas Department of Fisheries): With the quantities of lionfish that we've found in our waters and the amount of food that they consume, it has the potential of really collapsing our commercially important species — our fishing industry in general.

DORNFELD: Tourism is a $5 billion-a-year industry and accounts for half the employment in the Bahamas. Anderson worries that the lionfish continue to devour colorful reef fish, divers will vacation elsewhere.

Researcher Mark Hixon says in some places, the damage is already done.

Prof. HIXON: I was diving on a reef I've studied since 1991 last week, and it was so degraded and there were so few fish in what used to be a teeming reef, that at one point I was overcome and went to tears.

DORNFELD: He says in the best case scenario, some natural control will kick in and lionfish will become a minor part of the Caribbean and Atlantic reef community.

For NPR News, I'm Ann Dornfeld.

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