by Larry Smith
The Bahamas is facing one of the most disastrous marine invasions in history.
No, we are not talking about illegal Haitians, Dominican poachers, or South American drug traffickers. But the fact is that what we are facing could literally destroy our reefs and fisheries - the species and ecosystems that define our culture and quality of life.
"They have just literally exploded through time," said Oregon State University marine biologist Dr Mark Hixon, who has spent years doing underwater research in the Bahamas. "It's like a plague of locusts, and we are not very optimistic at this point that eradication is possible."
The threat comes from an exotic foot-long invader known as the lionfish. And for the first time, researchers in the Bahamas have documented just how dramatically this little fish can impact coral-reef ecosystems throughout the region by decimating a wide range of native populations through predation and competition.
The lionfish originates in the Indo-Pacific region, and has a colourful plume of spines that makes it a favourite of fish hobbiests around the world. Scientists say it was introduced into the Atlantic at Biscayne Bay, Florida, when several individuals were released from an aquarium during Hurricane Andrew in 1992. It has proved to be the most 'successful' introduction of an exotic species in this part of the world - with potentially devastating consequences.
Over the years lionfish have spread rapidly northward along the US eastern seaboard, and southward into the Caribbean. They have been sighted as far east as Bermuda, as far north as Rhode Island, and as far south as Jamaica and the Cayman Islands, with unconfirmed reports from the Yucatan Peninsula, Puerto Rico, and the Lesser Antilles. And they are now common throughout the islands of the Bahamas.
A voracious predator, the lionfish is undergoing a population explosion in the Bahamas, where it has no competition and few natural predators to keep it under control. Researchers say that the fish which inhabit Atlantic coastal reefs have never seen such an energetic and effective hunter in their midst.
“The threats to coral reefs all over the world were already extreme," Dr Hixon said, "and they now have to deal with this alien predator in the Atlantic. These fish eat many other species and they seem to eat constantly.”
And if the population explosion continues, he told Tough Call, the risks for the Bahamas are many: "There may be less food fish for people as lionfish consume juvenile grouper and snapper. There may be fewer grazing fishes, which help to keep corals from being overgrown by seaweeds. There may be fewer large predators as lionfish eat their young, predators which have been shown to help stabilize fish populations. In short, the lionfish invasion has the potential to become the most disastrous marine invasion in history."
It has taken years of scientific effort to arrive at this unhappy conclusion. At first, the zebra-striped invader was seen by many as a good photo opportunity on the reef. But some of the very dive operators who enjoyed snapping their picture are now the greatest advocates for their eradication. They realise that the pretty little fish could soon destroy the coral reef communities that tourists come to see.
"I think at the best they will have a huge impact on reef fish, and at the worst they will result in the disappearance of most reef fish," said Bruce Purdy, who runs a liveaboard dive fleet in the Bahamas called Blackbeard's Cruises. In fact, it was the crew of one of Purdy's vessels that made the first documented sighting of a lionfish in Bahamian waters in November, 2004.
Lionfish can eat other fish up to two-thirds their own length, while they are protected from predators by long, poisonous spines. In the Pacific, other fish have learned to avoid them and they also have more natural predators, particularly large groupers. But Atlantic fish have never seen them before, and few local predators will eat them.
Because of their natural defense mechanisms, lionfish are afraid of almost no other marine life. And the poison released by their sharp spines can cause painful stings to humans – even leading to death for some people with heart problems or allergic reactions.
“These are pretty scary fish, and they aren’t timid,” Dr Hixon said. “They will swim right up to a diver in their feeding posture, looking like they’re ready to eat. That can be a little spooky.”
And according to Eleanor Phillips, a former fisheries officer who now works for the Nassau office of The Nature Conservancy, Bahamians can expect smaller fishing catches soon: "Lionfish feed on young grunts, snapper, grouper and other fish that are important for food and export. If this invasion continues, our fishing industry could suffer."
Dr Hixon is a scientific advisor to the Bahamas National Trust, and has studied reefs in the Exuma Sound since the early 1990s. He first came across a lionfish near Lee Stocking Island in 2005. And since then, the lionfish population in the Bahamas has multiplied.
They are seen in every habitat throughout the archipelago: in shallow and deep reefs, off piers and beaches, as well as in coastal mangroves that are important nursery habitats for juvenile fish.
"During the summer of 2007, we sighted over 100 lionfish in the vicinity of Lee Stocking; three in the Exuma Cays Land and Sea Park, and two at Cat Island," Dr Hixon reported in a recently-published research paper that he co-authored with graduate student Mark Albins. "The clear increase in lionfish numbers at these regularly visited study sites indicated an extremely rapid expansion within the Bahamas."
So Hixon and his colleagues decided to interrupt their regular research on the ecology of reef fish and conduct a special experiment to determine whether, and to what extent, lionfish affect populations of native fish on Bahamian reefs. They used an area of experimental patch reefs near Lee Stocking Island that had been established back in the 1990s - at least a kilometre away from other natural reefs.
An initial survey counted the number of juvenile native fish living on the reefs and confirmed that no lionfish were present at the outset of the experiment. With some reefs designated as a control (lionfish absent) and others as a treatment reef (lionfish present), single individuals were then introduced to each of the lionfish-present experimental reefs. Following these transplants, divers re-counted the number of juvenile native fish.
The result? Lionfish reduced the abundance of small fish on coral reefs by 80 per cent in just five weeks.
In Hixon's experiment 38 fish species were recruited to both lionfish-present and lionfish-absent reefs. Of these 38 species, 23 suffered reduced recruitment in the presence of lionfish. And stomach content analyses and observations of feeding behavior showed that reductions in recruitment were almost certainly due to predation by lionfish.
Recruitment is defined by researchers as the survival of individual fish that settle in a particular habitat area. It is an important variable in terms of the population structure of individual marine species.
"The large reduction in recruitment suggests the possibility that lionfish may compete with native (fisheaters) by monopolizing this important food resource," the study concluded. "Also, by decreasing recruitment, lionfish have the potential to decrease the abundance of ecologically important species, such as parrotfishes and other herbivorous reef fishes, which are crucial for preventing seaweeds from overgrowing corals.
"It is also important to note that lionfish have the potential to act synergistically with other existing stressors, such as climate change, overfishing, and pollution, making this invasion of particular concern for the future of Atlantic coral reefs."
Options to manage the threat are limited, scientists and fishery managers agree. Dr Hixon has called for targeted control efforts to be initiated as soon as possible, particularly in vulnerable or valuable reef areas. Measures to help the recovery of effective predators would also help. For example, groupers eat lionfish in the Pacific, but have been heavily over-exploited in this part of the world.
"Our hope is that the Bahamian government will actively promote local controls, possibly including a targeted fishery and perhaps even bounties," Dr Hixon said. "Lionfish are easy to capture underwater with dip nets and they taste like chicken. Unfortunately, they can live to at least several hundred feet depth, which is beyond the range of most divers."
According to Director Michael Braynen, interest in the lionfish invasion at the Department of Marine Resources is high: "We are holding a workshop in Nassau next month for about 40 people, including ministry employees from around the country, to train them in the collection and handling of lionfish," he told Tough Call.
"The idea is to give them knowledge they can pass on to fishermen and others in the islands to encourage the use of these fish as a food source, and even to sell them once the spines have been removed. We want to promote that as one of the few control measures we have available."
Braynen is also recommending modifications to fishery regulations that will allow dive and resort operators to use SCUBA gear to conduct lionfish cleanup projects at specific locations. It is currently illegal to use SCUBA gear to fish, or to fish within a certain distance of the shoreline in some areas.
There is a sense of urgency involved because scientists are now convinced that the rapid reproduction potential of the lionfish, combined with its ability to seriously impact the populations of other fish, could disrupt entire reef ecosystems - with unpredictable results.
"We have to figure out something to do about this invasion before it causes a major crisis," Dr Hixon said. We basically had to abandon some studies we had underway on the population dynamics of coral reef fish, because the lionfish had moved in and were eating everything.”
For the past two years divers, scientists and government officials have been collaborating on a survey that reports, counts, tags, catches and dissects lionfish found in Bahamian coastal areas.
This project has also determined that lionfish are spreading rapidly and eating juvenile snappers and groupers, as well as competing with adult reef fish for food. In one recent survey off southwestern New Providence, for example, 124 lionfish were caught within two hours in a one-mile radius.
The Bahamas National Trust and other environmental groups have even been holding cookery demonstrations on some islands, to show that lionfish are good to eat once the spines have been removed.
As an example of what the future could hold, experts point to the Nile Perch, a large freshwater fish that caused the extinction of hundreds of fish species when it was introduced into Lake Victoria in Africa. The World Conservation Union calls it one of the 100 worst alien species invasions.
"Those kinds of things happen repeatedly in fresh water," Dr Hixon commented. "But we've not seen such a large predatory invasion in the ocean before."