Wednesday, April 13, 2011

Beauty as the Beast: lionfish invasion in the Caribbean

It is an unfortunate situation when something of beauty is at risk of being destroyed through no fault of it's own. But off the coast of Florida and throughout the Caribbean, that is the fate that awaits the lionfish (genus: Pterois). For all its graceful movement, striking color, and ornamentation, it is, regrettably, an invader that threatens the ecological balance of reef communities throughout the region.

I just returned from two weeks at sea along the shallow banks northwest of Grand Bahama, and with every reef dive I undertook I was guaranteed at least a half dozen sightings of these small Indo-Pacific predators. Known for having a voracious appetite to match its venomous spines, it was reported in one study that a lionfish can consume three-quarters of a reef's fish population in as little as five weeks. Left unchecked, the lionfish threatens the Bahamas' annual $5 billion tourism industry (that's billion with a "B") and nearly half of the island's employment. Bathers can get stung by the lionfish's dorsal spines or divers can find reefs denuded of colorful tropical fish and this can spell economic ruin for many Caribbean nations.

So, how did this all come about? How did a fish found in the South Pacific make its way halfway across the planet? Well, it certainly would need some help, an accomplice or two.

And that would be us.

The lionfish invasion in the Caribbean is a textbook example of invasive species distribution. Because of its beauty, juvenile lionfish are a popular addition to home saltwater aquariums. That is, popular until your other aquarium fish begin to disappear one by one as the lionfish grows and its appetite blossoms.

So, could it have found itself in the Atlantic when a frazzled home aquarist released it into the wild? Possibly, although it has been reported that the pivotal moment may have occurred in 1992 when Hurricane Andrew battered the southeast coast of the U.S., smashing an aquarium tank in Florida, and releasing six lionfish into open sea. Through the 90's, lionfish expansion was slow, but the first one showed up in the Bahamas in 2005. Two years later, the population exploded (some studies have indicated that a possible reason for the lionfish's successful growth is due to its resistance to many of the parasites commonly found in the Caribbean). The invasion was in full force and the war was on.

Over thousands of years, the lionfish found its proper place in the Indo-Pacific as both predator and prey. Groupers and other large fish fed on them, helping to control their numbers. But in the Bahamas, groupers have been overfished, so there aren't enough of these controlling predators to do the job (and even juvenile groupers are at risk of becoming a lionfish's next meal).

NOAA, the National Oceanic and Atmospheric Administration does not mince words when describing the lionfish invasion. "
With few known natural predators, the lionfish poses a major threat to coral reef ecosystems in the Caribbean region by decreasing survival of a wide range of native reef animals via both predation and competition," says NOAA's Office of Research. "It was not unusual to observe lionfish consuming prey up to 2/3 of its own length. Results of the experiment show that lionfish significantly reduce the net recruitment of coral reef fishes by an estimated 80%. The huge reduction in recruitment is due to predation and may eventually result in substantial, negative ecosystem-wide consequences. 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."

While in the Bahamas, I saw signs and posters proclaiming that the only good lionfish in Caribbean waters was basically a dead one. Crew members would regularly dive with short tri-tip spears in hand, looking under reef ledges - a favorite lionfish hangout - and stabbing any lionfish they came upon, leaving it there perhaps to eaten by a scavenging shark.

In fact, several of the crew reported trying to entice Caribbean reef or lemon sharks to feed on a speared lionfish in the hopes that the sharks would develop a taste for the enemy invader. The sharks would have to learn the best approach to avoid a discomforting sting and, in fact, I saw one shark make repeated bites - spitting out the lionfish until it found the right angle by which it could comfortably consume the free meal.

While the lionfish is one of the tropical ocean's most beautiful inhabitants (and one of my personal favorites), as an invasive species it unintentionally poses considerable risk to the Caribbean marine ecosystem. Could a natural balancing mechanism take hold through predation by fish who discover a new potential prey item in their midst? Or will mankind, having been responsible for the lionfish's introduction in the Caribbean in the first place, now have to take extraordinary steps to eradicate this species? To date, the success of the lionfish shows that there are no easy answers, as is often the case with other invasive plant and animals species around the globe.

Read about the lionfish invasion in
Read about
NOAA studies of the lionfish invasion.

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