The "encounter was unexpected and mesmerizing,” the scientists write in their study, published in PeerJ. Off the Panamanian coast, a dense cloud of crabs is swarming. Scientists from the Woods Hole Oceanographic Institution in Massachusetts were studying the Hannibal Bank Seamount when they spotted opaque sediment moving along the sea floor. The source was an insect-like swarm of thousands of red crabs moving along the bottom of the ocean in a way that scientists had never observed before among crabs or similar marine life, The Guardian reports.

The crabs were swimming, in mass numbers, through oxygen-deprived hypoxic waters—which are becoming more common, thanks to climate change—1200 feet under the ocean surface, as submarine video and images from autonomous underwater vehicles show. The extreme environment, where few other species can survive, may be a place where the crabs hide out from predators like tuna, the researchers suggest. Next, the team plans to map the area with drones and return for additional research.

[h/t The Guardian]

Screenshot and video via Woods Hole Oceanographic Inst. on Vimeo.