Deep-sea squid filmed using mud camouflage on the abyssal seafloor

A deep-sea squid has been filmed concealing itself in full view by coating its body in mud and holding its tentacles stiffly upright to merge with the seabed.

For much of the sighting, just two pale tentacles protruded from the sediment, remaining motionless like the stalks around them.

The behaviour was captured at a depth of more than 13,000 feet (nearly 4,000 metres) on an abyssal plain, a landscape largely defined by fine mud and scattered structures.

While Alejandra Mejia-Saenz of the Scottish Association for Marine Science (SAMS) piloted a remotely operated vehicle over the seafloor, the squid briefly emerged from its cover before disappearing beneath it again.

That short appearance demonstrates how active camouflage influences what deep-sea surveys are able to record.

It also affects what such surveys fail to detect, a significant concern as scientists increasingly rely on these observations to evaluate ecological risks and inform decisions on seabed mining.

Sediment-based camouflage

A detailed examination of the recording revealed that the squid had been lying under a light covering of mud shortly before swimming away.

Researchers watched the behaviour using a remotely operated vehicle: a ship-controlled, tethered robot fitted with several cameras.

The mud probably obscured the animal’s outline from predators while still permitting water to flow across its gills.

Fine sediment could also dampen movement, although the particles may cling to the skin and make the squid harder for cameras to see.

Body position and concealment

The animal, a cephalopod related to squid and octopuses, held itself upside down immediately above the muddy seafloor.

This position probably supported respiration by leaving its siphon unobstructed and channeling oxygen-rich water towards the gills.

Scientists estimated that its body was about four inches (10 centimetres) long, while its two strikingly pale tentacles extended almost nine inches (23 centimetres) into the water.

Once the squid had swum away, the team could not determine whether it had deliberately burrowed into the sediment or had merely settled into loose mud.

Camouflage as deception

With its rigid tentacles held vertically, the squid resembled a stationary stalk on the seafloor rather than potential prey.

Biologists describe this as masquerade – a type of camouflage in which an animal imitates a commonplace object within its surroundings.

Here, stalks of nearby sea sponges and worm tubes may lead predators to ignore the unmoving form.

The disguise probably succeeds only while the squid stays perfectly still, as even a slight twitch could expose muscle or eye movement. This pose could also assist the squid in feeding.

A low-energy feeding strategy

Because small creatures often collect around stalks and tubes, scientists have suggested aggressive mimicry – a tactic that attracts prey instead of merely concealing an animal from predators – as a further reason for the tentacle display.

Whiplash squid have numerous tiny suckers along their tentacles, enabling drifting crustaceans to adhere before the arms draw them in.

As food is limited in the abyss, an ambush method involving little swimming may save energy over extended periods.

Where few animals are seen

Sightings of this kind have taken place on abyssal plains – extensive areas of deep seabed blanketed in fine sediment and seldom examined by people.

Within the Clarion-Clipperton Zone, scientists recorded only 33 cephalopod sightings over more than 3,100 miles (5,000 kilometres) of survey transects.

“Many people tend to think of abyssal plains as deserts in the deep sea, but there’s probably a higher level of diversity than we think, given the elusive behavior of these creatures,” said Mejia-Saenz.

So few observations leave substantial gaps in knowledge of food webs, as predators and prey may remain undetected during the long intervals between surveys.

Limits of seafloor surveys

Video surveys of the seabed may fail to record fast-moving animals because lights, noise and water jets can warn them of approaching equipment.

Camouflage creates an additional barrier, with a mud-coated squid merging into the sediment until it moves or catches the light.

“This was an example of the unexpected behaviors seen in the abyss and showed how little we still know about that environment,” said Mejia-Saenz.

When ecologists use this footage to calculate abundance, they could underestimate predators that evade cameras and conceal themselves effectively.

Impacts of deep-sea mining

Growing interest in polymetallic nodules – potato-sized rocks containing manganese and other metals – is bringing more vessels to these abyssal plains.

These nodules form hard areas where corals and sponges can attach, meaning that removing them also eliminates this seafloor structure.

One long-term seabed experiment showed that animal communities in disturbed locations remained altered 26 years after a trial ploughing operation.

If mud and stalks help squid to survive, the loss of this patchy habitat could alter where predators search for food and where prey congregate.

Seeing more than expected

New camera systems can remain quietly on the seafloor for prolonged periods, giving wary animals time to return to normal behaviour after the lights and motor noise have subsided.

Longer observation with minimal disturbance lessens the trigger effect that can make animals flee or freeze when equipment initially arrives.

Teams at NOC and SAMS are extending this work through focused squid and octopus surveys, employing broader lighting and several camera angles to document behaviours missed during brief visits.

Protecting hidden species

The footage reveals a squid using mud, posture and immobility as camouflage to disappear into its environment, and possibly to catch food.

These longer and quieter observations are particularly valuable in areas being considered for mining.

More complete records of concealed animals can shape environmental regulations, since conservation plans rely on identifying the seafloor features that sustain species inclined to remain unseen.

Image credit: National Oceanography Centre/SMARTEX Project (NERC)