The ocean is a deeper hue of blue off the coast of Florida. Thirty meters (100 feet) down, the water is clear. The colors of the reef are dazzling. Near an orange barrel sponge is a group of fish. They seem to hang motionless. They look like a herd of zebras. But their stripes are reddish‑brown and white.

A diver appears. He aims a speargun at the head of the nearest fish. He pulls the trigger and strikes the fish. None of the other fish move. It’s as if they hadn’t noticed. The diver shoves the dead fish into a pouch. Then he takes aim again.

diver

A Fish Out
of Its Waters

Why would a diver kill a lionfish? Because lionfish are not a part of this environment. They are an invasive species. They hurt the local fish population. They hurt the reef, too.

Lionfish are native to the South Pacific and Indian oceans. There, they live in balance with other creatures. In the Atlantic Ocean, lionfish have no predators, so there is less balance.

Getting a Fin‑hold

So…how did these lionfish get in the Atlantic Ocean? There are some interesting theories: They arrived here trapped in ballast tanks of cargo ships. Or, a breeding pair escaped from an aquarium during Hurricane Andrew.

Most likely, tropical fish owners dumped their lionfish in the sea. This can happen once the fish get too big for their aquariums. The first report of lionfish was in 1985. They were found off the coast of Florida. Since 2000, the population has exploded.

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How Bad Is It?

In 2010, scientists named the lionfish a major threat to biodiversity. In some places, lionfish have reduced fish populations by 80 percent. How?

Unlike many other fish, lionfish never say no to food. They can eat one to two fish per minute. This adds up to hundreds of thousands of fish a year. They feed mostly on small fish. Yet, lionfish can wipe out entire groups of crustaceans, like shrimps, too. They also eat the young of larger fish. This makes it hard for some species to grow in number.

A lionfish swims near a mangrove forest.

New Rules

Mangrove forests have always been a safe haven for young reef fish. The underwater roots of mangrove trees provide both food and cover. Few predators hunt in its brackish waters. But lionfish don't follow these rules. They hunt there with ease. This makes them especially dangerous.

This young snapper is being cleaned by humpback cleaner shrimp.

Lionfish disrupt coral reefs, too. Cleaning stations there are “safety zones.” Larger fish line up to get parasites picked off of them by smaller fish. The small fish get a meal. The large fish get clean. And no fish gets eaten while the work is being done. Unless a lionfish comes by!

Lionfish also eat many fish that eat plants and algae. Algae are a type of plant that grow on corals. When the fish that eat them are gone, algae grow out of control.

Algae cover corals, choking out the light they need. This leads to the loss of habitat for all reef creatures.

These lionfish crowd together on a coral reef.

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Wildlife

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A Fish Out
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Getting a Fin‑hold

How Bad Is It?

New Rules

A Fish Out of Its Waters

Getting a Fin‑hold

A Fish Out
of Its Waters