How Bad Is It?

In 2010, scientists named the lionfish invasion one of the top 15 threats to global biodiversity. That means lionfish are capable of completely changing an entire ecosystem. And they have. In some places, lionfish have reduced native fish populations by 80 percent. How is that possible?

Lionfish don’t act like some other predators, which eat a lot all at once and then don’t hunt for several days. Lionfish never say no to food. They can eat one to two fish per minute. Over a ​​​​​​​year, this works out to hundreds of thousands of fish eaten per acre just by lionfish.

While they feed mostly on small fish, lionfish can wipe out entire groups of crustaceans, such as shrimps, too.

They also eat the young of larger fish. This makes it hard for some endangered or threatened species, like the Nassau grouper, to rebuild its population. This is especially true when the grouper is already competing with lionfish for living space on reefs.

A lionfish swims near a mangrove forest.

New Rules

Lionfish behave in unexpected ways. This makes them more dangerous than predators that “play by the rules.” Here’s an example. Mangrove forests have always been a safe haven for young reef fish. These stretches of sea between rivers and oceans are brackish. That means they are a mix of fresh- and saltwater.

These underwater forests of mangrove roots provide baby fish, or fry, with food and cover. Most ocean predators don’t hunt there. The lionfish hunts there with ease, roaming around and hoovering up small fish.

This young snapper is being cleaned by humpback cleaner shrimp.

Lionfish disrupt reef behavior, too. For example, some larger fish line up to get parasites picked off of them by smaller fish such as blueheaded wrasses. These cleaner fish get an easy meal. The larger fish get clean and enjoy better health.

As part of the bargain, the larger fish don’t eat the cleaner fish while the work is being done. This is a safety zone for these smaller fish. But lionfish simply see these stations as buffets. They swim into the stations and scarf up any fish that will fit inside their jaws.

Fish aren’t the only organisms threatened by lionfish. Many reef corals are also under attack. When lionfish eat too many planteating fish, there’s nothing to eat the algae. That’s when the algae grow out of control.

Algae cover the corals, choking off the light that corals depend upon. This happened in the Bahamas between 2003 and 2009 when lionfish ate too many young parrotfish. The algae grew so much, it killed the corals. It created a chain reaction. It led to a serious loss of habitat for all reef creatures.

These lionfish crowd together on one coral reef.