Moving 3,693 metres below the Arctic Ocean surface | Polarjournal

Exceptional images of a species of octopus from the Cirrina order reveal some hidden talents of the Dumbo octopus living at the bottom of the Fram Strait in the Arctic Ocean.This is the first time the animal has been documented feeding – a small step for underwater observation, a big step for science.

At a depth of 3,693 meters in the Arctic Ocean, where pressure is 369 times higher than at the surface, sunlight is absent, temperatures are around 0°C, and sound is almost non-existent, Dumbo octopuses (Cirroteuthis muelleri) live a silent, slow life. Remarkable images of this animal unveil an as yet unknown and natural behavior in an environment inaccessible to common people. Dumbo octopuses can be seen drifting along the seafloor, spreading out and then contracting into a slightly accelerated flapping of their fins before rising back into the water column.

The images were published in the Journal of the Royal Society on June 22 by Alexey Golikov and his colleagues, German, Norwegian and Russian marine and polar oceanographers. Coincidentally, also this month, the International Seabed Authority is pushing forward the issue of mining resources at these depths, an issue where the institution is torn between economic attraction and scientific caution, between the potential presence of rare metals and the great uncertainties beneath the ocean’s surface.

What does the octopus do when it moves like this?

The researchers noticed octagonal marks on the surface of marine sediments, corresponding to their 8 arms moving over the seabed. Image: A. Golikov and al. / AURORA / GEOMAR / The-Royal-Society / CC-BY-40

The octopod’s movements on the seabed probably enable it to catch its prey. “They coincide with a rapid movement of the fins, from 24 to 34 beats per minute, probably to increase the downward pressure on the prey, which is trapped between the octopod and the seabed,” the authors state.

What prey is there in these near-abyssal environments?

“There are copepods and other small crustaceans,” explains Alexey Golikov. “We assume that they are taken from the surface and from the upper layers of the sediment. Its cirri and jaws, a kind of beak, can be used for this.” Cirri are small, long, slender appendages that point along its tentacles. They are not very well developed […] and are not used for prey capture by our species”, adds the researcher.

How can we tell from the videos that it’s feeding?

The footage shows the octopus releasing a kind of mucus, which the researchers describe as “the remains of prey falling down the octopod’s arms”. Once the octopus has done its job, it rises up into the water column and drifts away with the current. The small octopuses then take on the shape of umbrellas. The reason for this is very likely to take advantage of the water current’s energy.

Using their fins, these animals can ascend up to 500 meters. However, they can’t go further than that due to the temperature and pressure. Wouldn’t they be better off feeding on the bottom? They’re using the water column’s currents to move from one productive area to another, thereby escaping the predators waiting for them buried in the sedimen

Thus, no predators in the water column?

At these depths, sperm whales, Greenland sharks, pilot whales and beaked whales can hunt the finned octopus, but “its gelatinous body gives a less clear echolocation signal than muscular prey”, says Alexey Golikov. Therefore, it has a fair chance at getting away undetected.

Currently, there are no data linking the Dumbo octopod with subsea mineral fields, but there are related deep-water species that do. For example the Casper octopod lives near polymetallic nodules in the Pacific. Image: NOAA / GEOMAR / Cell Press

With these findings, it’s clear that the Dumbo octopus is part of a living web that traps carbon in the oceans. That’s one more piece in the puzzle on their lifestyles. “There’s no doubt that there’s still a lot to discover,” assures Alexey Golikov.

Camille Lin, PolarJournal

Source Golikov, A.V et al (2023). Miles down for lunch: deep-sea in situ observations of Arctic finned octopods Cirroteuthis muelleri suggest pelagic-benthic feeding migration. Proc R Soc B: Biol Scie 290, 20230640.

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