It probably started in the 1980s, with a few tropical fish hobbyists thinking they were doing the humane thing by dumping unwanted pets in the coastal waters of Florida. But introducing the lionfish, which is native to the Indo-Pacific, to the Atlantic Ocean has turned out to be one of the cruelest and most catastrophic tricks ever played on an ecosystem. Now, with the fate of numerous species hanging in the balance, a new paper in the journal Ecological Applications says that scientists have for the first time found a practical way to control the problem.
Lionfish are flamboyantly colorful fish, up to 18 inches in length, striped, and having long, fluttering venomous spines sticking out in all directions. They’re appealing to have in a fish tank. But since their release into the Atlantic, they have spread across an area of 1.5 million square miles, from Venezuela to North Carolina, with stray sightings as far north as southern New England.
In the Caribbean, according to one researcher, it’s common to see lionfish “hovering above the reefs throughout the day and gathering in groups of up to ten or more on a single coral head." She might just as well have said “hoovering,” because of the speed and thoroughness with which lionfish wipe out native fish populations. They typically flutter their fins to herd smaller fish into a group, and when they have cornered their prey, they pounce.
Because of their extraordinarily painful venom, lionfish have no natural predators. As with many other invasive species, eradication appears to be impossible. Lionfish can repopulate shallow reefs from deepwater populations lurking farther off the coast.
But the study suggests a cost-effective alternative. Getting rid of most—but not all—the lionfish on a given site appears to provide enough relief to allow for the rapid recovery of native species, including commercially important fish like Nassau grouper and yellowtail snapper.
Oregon State University researcher Stephanie Green and her coauthors started with a computer model to calculate a threshold for different habitat types—that is, how many lionfish a site could tolerate and still function normally. Then they tested the model in the field, at 24 coral reef sites near Eleuthera Island in the Bahamas.
The model didn’t make it easy on the field team. To get to the threshold, they had to remove 75 to 95 percent of the lionfish, with the help of nets and spears. On a typical reef site, which is about a third the size of a basketball court, it took about 60 minutes of dive time. Completely eradicating the lionfish would have taken 78 minutes, or 30 percent longer, and that is apparently the difference that makes the method practical.
The researchers then followed up at regular intervals for 18 months. On test sites where the lionfish population was below the threshold, native prey species quickly rebounded, with a 50 to 70 percent increase in total biomass. On sites where the lionfish remained above the threshold, native species decreased by about half.
As that suggests, leaving the lionfish alone is no longer an option, or rather, it’s an option that leaves some native species bound for extinction. But with limited funding for fisheries management across such a vast stretch of ocean, the question is where to apply the control method for the maximum benefit. Because marine reserves typically allow no taking of fish, they are in danger, the new study warns, of becoming “de facto reserves for lionfish.” Mangroves and shallow reefs that serve as nursery sites for young fish are also a likely priority for control measures.
The good news is that there is now a remedy for what had seemed like an unstoppable invasion. But it won’t come cheap, and it should serve as yet another reminder that owning pets comes with grave responsibilities.
Introducing alien species to any habitat can quickly lead to catastrophe, both for wildlife and for us: Not even counting invertebrates, such as Asian long-horned beetles, that are killing off great swaths of forest, invasive species now cost the American public $120 billion every year.