AT BLOODY BAY MARINE PARK, just off the north shore of Little Cayman, I sink into the blue abyss. Straight ahead and straight down there is nothing but blue; a dizzying empty space where sunlight streams down and down into darker places well beyond my reach.
But up close, the wall of coral is covered in giant barrel sponges as tall as a man, bright purple vase sponges, green and red corals and creatures that creep, crawl and swim within and among them. These are reefs I know well, and for almost 15 years I have been returning to the spectacular drop-off at Bloody Bay, where the underwater scenery is as dramatic and mesmerising as anywhere I have dived.
I spot a seahorse anchored to a whip coral by its tail, a coral-clinging crab with legs spread almost a metre wide and a baby hawksbill turtle rocketing to the surface for a breath of air.
And there, spiralling up from the depths, come three graceful Caribbean reef sharks, curious and skittish.
Suddenly, I notice Peter, my diving buddy, gesticulating angrily: he points with one hand and pulls the trigger on an imaginary gun. It is not the sharks he is angry at, but a brightly coloured fish covered in feathery spines.
I recognise it immediately as a lionfish – distinctive with its tracery of red-brown stripes and the highly venomous spikes all along its back and protruding from its pectoral fins too.
I have seen thousands of these fish in the Indian and Pacific Oceans, but they shouldn’t be here in the Caribbean.

THESE LIONFISH SCARE ME,” Peter tells me on the boat after we surface. “Two or three years ago we would see the odd one here and there, but now on every dive they’re there. I’ve been diving these reefs for over 30 years, and I’m worried that these fish are taking over.”
Much as I am fond of these graceful tiger-striped predators that seem to hover as effortlessly as a soaring bird on the wing, the facts about lionfish are frightening.
A female can produce 2 million eggs a year – eggs that float in a jelly-covered bundle that other fish apparently don’t find tasty. The eggs and young drift for about 45 days, allowing them ample time to reach new habitats.
To learn a bit more, I visited the Central Caribbean Marine Institute on Little Cayman. There scientists are studying the invasion population of lionfish, more properly known as Pterois volitans.
Morgan Edwards, a post-graduate researcher at the Institute, invites me to watch her dissecting the fish. Even when dead they are beautiful, with a maze of dark red stripes all over their heads and bodies, protective spines covered in a web of fine skin and delicate frilly tassels of skin hanging from their mouths.
After measuring its length, weight and other details, Morgan removes the stomach from each fish and opens it to find out what they have been eating: shrimps, baby grouper, damselfish and crabs.
“Their stomach can expand up to 30 times its volume,” Morgan explains, “and they can swallow any other fish up to two-thirds their own body length. But they seem to have no natural predators here in the Caribbean.”
Mature females produce about 30,000 eggs every four days. In the Caribbean, they are growing larger than they do in their native waters – up to 45cm long – and they are
stealthy ambush predators.

THE “LOCAL” FISH HAVE BEEN SLOW to learn that their new neighbours will hoover them up in an instant. And one researcher has recently discovered that lionfish have a cunning trick. They “puff” water through their mouths to simulate a current – and small fish generally swim into a current headfirst – straight into range of the lionfish’s cavernous jaws.
No-one knows how lionfish got into the Caribbean. One theory is that they escaped from a Florida aquarium during a hurricane about 10 years
ago. Others believe tropical fish-keepers released their pets into the sea when they grew too large to keep at home.
It doesn’t really matter how they got there, but since 1992 they have spread from Florida up the east coast of the United States into the Carolinas.
About six years ago they crossed the western Atlantic to Bermuda, and then drifted south to the Bahamas, Jamaica and Cuba.

IN 2008 THE FIRST LIONFISH was spotted at Bloody Bay on Little Cayman. One year later there were hundreds, and now thousands. And they have now gone south as far as Venezuela.
Capable of surviving in waters with an annual mean temperature as low as 10°C, Indo-Pacific lionfish have been found as far north as Long Island (New York), and are now creeping southwards around the tip of South America.
“This isn’t just an invasion,” said Dr Carrie Manfrino, Research Director at the Central Caribbean Marine Institute, “this is an explosion. No invasive tropical fish species has ever survived so successfully outside its own home eco-system like this.”
Regular diving expeditions to cull lionfish have been authorised by Cayman Islands Department of the Environment in collaboration with the Institute. But no-one is sure that anyone can catch enough lionfish to make a difference.
One study in the Bahamas showed that lionfish reduced native species populations on one reef by almost 80%.
In several Caribbean countries I have heard divemasters and recreational divers moaning about lionfish. One dive leader talked in terms of an underwater apocalypse, in which reefs would be denuded of almost every local species, leaving only lionfish.
There have been widely publicised attempts to put lionfish on the menu in Caribbean restaurants, in the hope that eating them will thin their populations.
Let’s face it – if we can fish so many marine species to the point of extinction, surely we can do the same for lionfish.
But it’s not that simple. The only effective way to catch lionfish is by hand, with divers spearing them and stuffing them into a mesh bag, a labour-intensive process that is costly.
And, given how quickly and efficiently they breed, how many fish would we need to catch to really reduce their numbers
in an attempt to learN more, I contacted Dr Jeff Hill, a professor at the University of Florida whose speciality is the spread of non-native species within fisheries.
He confirmed that to his knowledge the red lionfish represented the most successful and widespread example of a marine species colonising a marine habitat. And he said that there was now evidence that two species are involved, not only Pterois volitans but also Pterois miles.
However, he offered a different perspective on how catastrophic the fish might be in the Caribbean in the long term. “We simply can’t predict what will happen,” said Hill. “And the reality is that there are other more serious problems with the marine environment – habitat loss, for example.
“Loss of habitat is a problem many orders of magnitude more pressing than the threat from invasive species.”
For the moment, it looks as if lionfish are here to stay in the Caribbean.
And what’s happening in relation to the native fish is consistent with the arrival of other non-native species in other eco-systems: they grow bigger, they are free of diseases and parasites that would normally reduce their numbers “at home” (in the Indo-Pacific), and they are not preyed upon by existing predators such as Caribbean grouper and snapper.
Will lionfish be the underwater equivalent of the cane toad (Bufo marinus), mistakenly introduced into Australia to eat pests on the sugar-cane crop The cane toad famously failed
to eat the cane beetles, but has instead devastated Australian populations of lizards, snakes and even crocodiles.
And let’s not forget what happened when human beings introduced the Nile perch (Lates niloticus) into Lake Victoria as an alternative food resource. It has now caused the extinction of more than 200 native fish species within the lake.
No-one knows if Nature will find a way of halting the lionfish’s progress.

DISASTROUS AS IT WOULD SEEM TO BE, I can’t help having a sneaking admiration for the success of lionfish.
In the Indo-Pacific, this is one of the fish that divers want to see. And there is some evidence that Caribbean grouper and snapper, and sharks, are beginning to acquire a taste for lionfish.
At a restaurant on Grand Cayman, I tasted my first lionfish fillet. Delicious.
For the moment, in the Caribbean, the lionfish has another claim to fame. It’s the one reef fish I can eat with a clear conscience.