Octopus Casper: Deep-sea octopuses require manganese nodules to lay their eggs

22.12.2016 08:35
Kategorie: News

Casper the octopus (and counterparts) threatened by deep-sea mining

For deep-sea octopuses, manganese nodules on the seabed are an important breeding ground. This is because they deposit their eggs onto sponges that grow on manganese nodules, according to a study by a German-American team of biologists published in the current issue of Current Biology. Unfortunately, this dependence on the manganese nodules does not bode well as the nodules are sought after by industry; thus, any collection of manganese nodules must be preceded by thorough investigations into the possible environmental consequences.

Gallery 1 here

Remember Casper? Not the fictional friendly ghost, but the tiny deep-sea octopus (Octopoda, subgroup: Incirrina) that became a social media star several days after a video of it was uploaded on YouTube this February. The US dive robot Deep Discovery had discovered it off Necker Island in Hawaii at a depth of 4,290 metres (as we had reported here). Researchers are now sharing the extensive wealth of knowledge about life in the deep sea and the ecological importance of manganese nodules (where Casper had been found), based on their observations of Casper and 28 other observations of similar octopuses elsewhere in the Pacific.

Guarding their eggs at record depth of more than 4,000 metres

At 4,290 metres depth, Casper's appearance represents the greatest depth at which such finless octopuses had been observed. Just six months earlier, researchers at the Alfred Wegener Institute, GEOMAR, Max Planck Institute for Marine Microbiology, and Centre for Marine Environmental Sciences (MARUM) had filmed and photographed other specimens belonging to a similar or related species at 4,120 metres depth, in the Peru Basin in southeastern Pacific Ocean.The diving robot ROV KIEL 6000 had been used for the recording, using a towed camera system (AWI-OFOS).

Where some octopuses lay their eggs

Two octopuses had been observed using guarding their eggs. “At a depth of 4,000 metres, these animals had deposited their eggs onto the stems of dead sponges, which in turn had grown on manganese nodules. The nodules served as the only anchoring point for the sponges on the otherwise very muddy seafloor. This means that without the manganese nodules, the sponges would not have been able to live in this spot, and without sponges the octopuses would not have found a place to lay their eggs,” said  lead author Dr Autun Purser, from AWI.

Gallery 2 here

Even when not seeking out a safe place to lay their eggs, octopuses can still be found near areas with manganese nodules and rocky protusions. “The video footage indicates that the animals have cleaned the seabed around the nodules. It probably looks like that because the animals have been filmed using their arms to dig into the sediment around the nodules, probably in search for food,” said co-author Henk-Jan Hoving, of the GEOMAR Helmholtz Centre for Ocean Research.

From the DISCOL experiment in the late 1980s, we discovered that many deep-sea animals required the presence of manganese nodules in their habitat. In the experiment, after manganese nodules were removed from an area in the Peru Basin, the community of animals, including sponges, that had been attached to the seafloor subsequently almost fully collapsed. When scientists returned to the same area 26 years later, many of the animal populations had not yet recovered. We had reported on this in a previous edition.

Our new observations show that we have to know about the behaviour of deep-sea animals and the specific way in which they adapt to their habitat in order to draw up sustainable protective and usage concepts,” said AWI researcher Antje Boetius, who had headed the previous expedition to the Peru Basin.

Gallery 3 here

Because Casper and his counterparts (as well as similar species) lay very few eggs and have very long reproductive cycles, they are under threat. The offspring of octopuses that spawn in waters at three degrees Celsius only hatch after four years. However, at the bottom of the Peru Basin, the temperature is just 1.5 degrees Celsius. This has led researchers to conclude that their eggs would need many years before they fully developed. Any disturbance during this period would have serious implications on the developing embryo.

Link to the study: http://www.cell.com/current-biology/fulltext/S0960-9822(16)31286-6