Stirring in the depths of the ocean off the coast of Panama is a giant swarm of creatures clambering over each other as they creep across the floor.

The terrifying sight was captured by biologists in the Pacific Ocean, filmed from the comfort of a nearby submarine.

The video footage shows thousands of the red crabs swarming in low-oxygen waters just above the seafloor.

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It’s the stuff of nightmares – thousands of red crabs creeping along with their claws outstretched. The terrifying sight (shown) was captured by biologists off the coast of Panama from a submarine

Jesús Pineda, a biologist at Woods Hole Oceanographic Institution (WHOI) and chief scientist on the cruise, called the encounter at the Hannibal Bank Seamount 'unexpected and mesmerising'.

His team, including scientists from Point Loma Nazarene University, San Francisco Estuary Institute, and Smithsonian Tropical Research Institute saw the incredible scene from manned submersible Deep Rover 2 in April 2015.

'When we dove down in the submarine, we noticed the water became murkier as we got closer to the bottom,' said Dr Pineda, lead author of the paper published in the journal PeerJ.

'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.'

Biologist Jesús Pineda and chief scientist on the cruise, called the encounter at the Hannibal Bank Seamount 'unexpected and mesmerising'. After the sub dive, the team used the SeaBED-class vehicle Jaguar AUV to gather additional images on the density of the crab swarm (image shown)

THE RED CRABS OF MEXICO While the swarming crabs may look a light shade of brown in the murky waters of the video, they are in fact bright red in colour. Pleuroncodes planipes, known as red crabs or tuna crabs, measure up to 5.1 inches (13cm) long and resemble a short lobster. The creepy creature was first described in 1860. It typically lives on the continental shelf of Mexico, south-west of San Diego, with the most southerly range in Chile. But in warmer years the crab’s range can extend north and is an indicator of an El Niño event. Advertisement

'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.'

The crabs were later identified by DNA sequencing as Pleuroncodes planipes, a species abundant in Baja California and found in the waters off the west coast of Baja California, Gulf of California, and the California Current.

The footage represents a new southernmost range of distribution for the species.

'No one had ever found this species that far south,' Dr Pineda said.

'To find a species at the extreme of their range and to be so abundant is very unusual.'

The crabs were later identified by DNA sequencing as Pleuroncodes planipes, (stock image of one pictured) a species abundant in Baja California and found in the waters off the west coast of Baja California, Gulf of California, and the California Current

His team, including scientists from Point Loma Nazarene University, San Francisco Estuary Institute, and Smithsonian Tropical Research Institute saw the incredible scene from manned submersible Deep Rover 2 (pictured above) in April 2015

The large aggregation of swarming red crabs was observed along the Northwest flank of the Hannibal Bank Seamount (location marked) at depths of approximately 1,164ft to 1,263ft (355 to 385 metres) in an area of 'hypoxic', or low oxygen level, water

WHAT ARE SEAMOUNTS? Seamounts are ecological 'hotspots' that are home to thriving communities of unique species. Because less than one per cent of these underwater mountains have been studied, the mechanisms that make them so biologically productive are not well understood. The focus of the Panama expedition was to learn more about both the biological and physical processes that make Hannibal Seamount such a rich ecosystem and the crab sighting was an unexpected surprise. The deep-water areas of Hannibal Seamount, which lack dissolved oxygen and are acidic, give scientists an opportunity to investigate how communities might look in the future as the ocean responds to climate change. Advertisement

The large aggregation of swarming red crabs was observed along the Northwest flank of the Hannibal Bank Seamount at depths of approximately 1,164ft to 1,263ft (355 to 385 metres) in an area of 'hypoxic', or low oxygen level, water.

'These crabs have been detected before in similar low oxygen conditions,' Pineda said.

'It could be that these low oxygen waters provide a refuge for this species from predators.'

Also known as tuna crabs because they are favoured prey for yellowfin tuna, Pleuroncodes planipes are an important food source for a variety of other fish, birds, and marine mammals.

They migrate up and down in the water column, which also makes them vulnerable to changing currents.

A few months after the expedition, thousands of red crabs washed ashore onto Southern California beaches during a massive stranding associated with El Niño warming conditions.

The crabs were observed at Hannibal Seamount (illustrated), off the coast of Panama. Seamounts are ecological 'hotspots' that are home to thriving communities of unique species