In their native home, lionfish have their own predators that keep their numbers in check. But in the Atlantic, sharks, barracuda, groupers, and eels that could eat lionfish steer clear of them. They’re deterred by the animals’ venomous spines, which deliver a painful sting. That’s given lionfish free rein to take over local ocean ecosystems they’ve invaded. When it comes to lionfish versus native predators, says Johnston, there’s no competition. “It is like someone coming into your home and kicking you out and eating all your food.”
Lionfish will eat almost any smaller-sized fish they come across, spreading their fins wide to corner their prey and then swallowing it whole. And they keep hunting even when their stomachs are full. A single lionfish can reduce the number of fish living on a reef by 80 percent in just five weeks. Reefs depend on small fish because they graze on aquatic plant-like organisms called algae. Without the fish, algae overgrow on coral and cause it to die.