Scientists at Cape Cod's Woods Hole Oceanographic Institution discovered what they've called a "cloud" off the coast of Panama at the Hannibal Bank Seamount. But, as their website reports, this so-called cloud was made up entirely of crabs.
"At first, we thought they were biogenic rocks or structures," Jesús Pineda, who led the expedition, told the Guardian. "Once we saw them moving — swarming like insects — we couldn't believe it."
The team published their findings Tuesday in the journal PeerJ. The team members said the swarm was like nothing they had ever seen.
The species, Pleuroncodes planipes, is known as the red crab because of its color, but is also referred to as the tuna crab because of its main predator. The crabs are usually between 1 and 5 inches long and its common habitat is Baja California, much farther north than the Woods Hole team found them, according to the paper.
"No one had ever found this species that far south," Pineda said in statement on the Woods Hole site. "To find a species at the extreme of their range and to be so abundant is very unusual."
A video released by Woods Hole shows the crabs moving over each other in a dense mass. According to the paper, the swarming creatures were jumping over each other and pulling out dead cohorts.
Pineda told the Guardian that he went searching through scientific findings for this behavior in similar species. He couldn't find anything.
"Nothing like this has ever been seen, where we have this very dense swarm at the bottom," Pineda said. "We have no idea why they might be doing this."
The crabs were found around 1,200 feet below the surface in water with very low oxygen, according to the release. This kind of environment is hard for most marine species to survive in.
The researchers plan on returning to the Hannibal Bank Seamount to further study the crabs, and also to study how life could function in similar low-oxygen, acidic waters that could occur more widely as a result of climate change.