Uncovering a Deep-Sea Swarm of Zombie Crabs

A swarm of crabs found off the Pacific coast of Panama. CreditJesus G. Pineda/Woods Hole Oceanographic Institution

By NICHOLAS ST. FLEUR

In the murky depths of Panama’s Pacific coast, marine biologists witnessed what looks like a scene from “The Walking Dead”: Thousands of crabs marching like a zombie horde.

The team stumbled upon the horror movie moment last April while exploring the aptly named Hannibal Bank Seamount, an underwater mountain home to a plethora of sea life.

At first they examined sea urchins, sponges and black coral from their submarine. But as they descended deeper into the darkness they noticed a thick layer of dirt and silt swirling along the seafloor.

They decided to investigate the disturbance.

“You’re a little bit afraid because you’re going into the cloud of sediments,” said Jesús G. Pineda, a marine ecologist from the Woods Hole Oceanographic Institution in Massachusetts, and the lead researcher aboard the submarine. “There was some mystery. You have no idea what’s going to happen.”

As they dove some 1,200 feet deep, the submarine illuminated the culprit: a swarm of red crabs scuttling across the seafloor.

“I was mesmerized,” said Dr. Pineda. “I just couldn’t believe it. It was very unexpected.”

This was the first time researchers recorded footage of the inch-long crabs carpeting Panama’s ocean floor, according to Dr. Pineda. He said it was unusual to watch the swarm crawl in the same direction, a behavior normally seen in insects.

Using DNA analysis they identified the crabs as Pleuroncodes planipes, or red crabs, which are usually found off the coast of Baja California. The team published their findings this week in the journal PeerJ.

But there is still a mystery: Dr. Pineda and his team said they aren’t sure why the crustacean congregation formed, and why it appeared so far south from where the crabs usually lurk.

Thousands of red crabs swarmed the ocean floor off the coast of Panama.

 By JESUS PINEDA, CHIEF SCIENTIST AT WOODS HOLE OCEANOGRAPHIC INSTITUTION on Publish DateApril 14, 2016. Photo by Jesus G. Pineda/Woods Hole Oceanographic Institution