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In 2005, 11-year-old Clay Steell was snorkeling near his home in the Bahamas when he came across a fish he’d only heard rumors about. He knew immediately what the brown-and-white striped fish was: a lionfish, the region’s new invader.
“A couple of months later, we were seeing them all over the place,” he recalls.
Native to Indo-Pacific reefs, lionfish were first recorded in the Bahamas in 2004, but they’d been swimming in the Atlantic off Florida since the 1980s—likely because fickle pet owners dumped them into the sea. Armed with venomous spines and without natural predators to dampen their numbers, the exotic fish quickly became a menace, gobbling up native species.
Years later, still intrigued by the lionfish that had mesmerized him as a child, Steell decided to study what makes it such an adept invader. As a master’s student at Ontario’s Carleton University in 2017 he wondered if the fish’s success had to do with its metabolism. He was also curious how climate change would affect its invasion streak.
Working from the Cape Eleuthera Institute in the Bahamas, Steell found that compared to other fish, lionfish are “more built for digestion than for swimming.” While most other species need to work to avoid predators, the spiny fish can kick back and digest.
When the sea is warm, they become even more efficient. Experiments show that at the region’s peak summer temperature of 32 °C, they spend 30 percent less energy on digestion. They also eat more voraciously and more often. All of that leaves the heat-loving fish with more energy to grow and reproduce—making them even better positioned to outcompete local species and wreak ecological and economic havoc in the ecosystems to which they’re introduced.
Previous research shows that once lionfish settle into an ecosystem, biodiversity decreases. They devour grazers, such as parrotfish and surgeonfish, which feed on algae that would otherwise smother corals. When lionfish eat cleaner fish, which other species visit to stay parasite-free, it has knock-on effects on ecosystems beyond those that lionfish have invaded, says Steell. And with such a large appetite, lionfish take food away from commercially profitable species, affecting local communities that rely on those fisheries.
In the past decade, lionfish have invaded the eastern Mediterranean Sea, which is warming up 20 percent faster than the rest of the ocean. Periklis Kleitou, a marine scientist at the University of Plymouth in England, worries that warming trend will only encourage the invasive species. That’s why studies like Steell’s are crucial for predicting how lionfish might disrupt the Mediterranean—as they have the Caribbean for decades—and what management strategies should be taken, Kleitou says. Cyprus has already borrowed one method from Florida: the lionfish derby, a competitive event to remove as many of the predators as possible.
Now, whenever Steell finds himself in the Bahamas, he goes out to the waters of his childhood to spearfish for the spiny invader. “Despite their beautiful appearance, I understand how much of a problem they are and how urgently they need to be taken off the reefs.”