Thousands of crabs are gathering off the coast of Panama, an event which is resembling an alien invasion, according to researchers. This occurrence is a surprise to researchers who have studied the animals.

Red crabs are massing on the Hannibal Bank Seamount, located in the waters near Panama. The animals are gathering in oxygen-poor water just above the seafloor, around 1,200 feet beneath the surface of the water.

Woods Hole Oceanographic Institution (WHOI) researchers studying biodiversity captured stunning video of the event.

Researchers aboard the Deep Rover 2 submersible, taking part in the last dive of a month-long investigation, recorded the unexpected encounter in April 2015. The team noticed the water was becoming murkier as they dove to greater depths.

"There was this turbid layer, and you couldn't see a thing beyond it. We just saw this cloud but had no idea what was causing it. As we slowly moved down to the bottom of the seafloor, all of the sudden we saw these things. At first, we thought they were biogenic rocks or structures. Once we saw them moving--swarming like insects--we couldn't believe it," Jesus Pineda, a biologist at WHOI, said.

Pleuroncodes planipes, also known as tuna crabs, are often found in waters off Baja California and the Gulf of California. They are not normally found as far south as Panama, and finding a large gathering of the creatures was especially surprising to investigators. This event marks the furthest south the animals have ever been seen.

The tuna crab, which are a favorite food of the large fish for which they are named, may have moved to the low-oxygen water as a means to avoid predators, which also includes marine mammals. Seamounts like the site of the gathering are under water mountainous regions, rich with a wide variety of life forms. The study which found the underwater meeting of crabs was aimed at discovering why the Hannibal Seamount is able to sustain such a wide range of plants and animals.

A large group of red crabs washed onto the beaches of southern California just months after the unusual gathering near Panama was recorded. Biologists believe this event was driven by warming water, heated by El Nino.

Analysis of the unisual gathering of tuna crabs was presented in the journal PeerJ.

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