Expedition Discovers Invasive and Huge Lionfish Thrive Deep Beneath Atlantic Ocean

First Posted: Jul 12, 2013 07:32 AM EDT

Deep beneath the surface of the Atlantic Ocean lives a voracious predator that gobbles down fish as it hunts in tropical waters. It's not a shark, though; it's not even a squid. Instead, this predator is the invasive lionfish--and it turns out that they're growing huge at 300 feet below.

Lionfish are native to the Indo-Pacific region. With their graceful, fan-like fins and their striking, striped patterns, these fish have long been used as popular aquarium pets. Unfortunately, this popularity is probably what introduced them to areas along the coast of the U.S. in the first place. It's very likely that someone dumped aquarium water into the ocean, either knowingly or unknowingly releasing the first lionfish into the wild.

While lionfish can appear as far north as New Jersey in the summertime, though, these creatures are usually limited by how warm waters are. That said, it seems that at least one population of these tropical fish have dived to depths and have thrived, growing large over the years. Since big fish in many species can reproduce much more efficiently than their younger counterparts, this phenomenon raises significant concerns.

"We expected some populations of lionfish at that depth, but their numbers and size were a surprise," said Stephanie Green, one of the researchers who participated in the dives in search of the lionfish, in a news release. "This was kind of an 'Ah hah!' moment. It was immediately clear that this is a new frontier in the lionfish crisis, and that something is going to have to be done about it. Seeing it up-close really brought home the nature of the problem."

Lionfish are predatory, and many of the fish in the Caribbean aren't quite sure how to respond. Their graceful, waving fins are actually spines which they use to paralyze their prey before gobbling them down. In fact, a study in 2008 showed that lionfish in the Atlantic have been known to reduce native fish populations by as much as 80 percent. Since they have no natural predators, the lionfish population has grown by leaps and bounds.

In this latest study, the researchers saw lionfish that were as much as 16 inches in length. While that may not see that big, it's enormous for a lionfish. It could have major implications for nearby species.

"A lionfish will eat almost any fish smaller than it is," said Green. "Regarding the large fish we observed in the submersible dives, a real concern is that they could migrate to shallower depths as well and eat many of the fish there. And the control measures we're using at shallower depths-catch them and let people eat them-are not as practical at great depth."

The findings have huge implications for the future of the Atlantic. The loss of herbivorous fish could set the stage for seaweed to potentially overwhelm the coral reefs and disrupt the delicate ecological balance in which they exist. This means that it's more important than ever to find out exactly how to stop the spread of lionfish.

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