The Neverending Bamboo Coral Story

Parts of this ridge segment was filmed in February 2024 during a Norwegian Offshore Directorate survey and while Heidi Kristina Meyer was annotating the publicly released footage afterwards, they noticed signs of what looked to be a bamboo coral garden in the footage. MAREANO made an extra station outside of its survey area to investigate it.

The ridge is steep on both sides and the scientists aboard the Research Vessel Kronprins Haakon are met with a view of the pink and purple soft coral Gersemia on the right and white glass sponges of the Rossellidae family on the left. After a long descent at almost a kilometer depth, the seabed appears on the video screen. Almost immediately Meyer, who is leading MAREANO’s first cruise to AMOR, sees dead bamboo coral fragments laying in front of the ROV and asks the pilots to zoom in on the fragments.

Meyer is sitting with the ROV pilots in their container while they are piloting Ægir6000 below the ship, the rest of the scientists on the shift are in the video room corresponding with the ROV container. The terrain is steep and difficult, and Meyer is uncertain if they will be able to find exactly what they are looking for. Once they give the go ahead, Ægir6000 starts to hover carefully forward on the narrow crest of the ridge, making sure the scientists in the video room have a clear view ahead of them. Approximately 20 minutes into the dive, Meyer starts to notice more bamboo coral fragments appearing in front of the ROV. Five minutes later, Meyer calls over the intercom to those in the video room that they think they have finally found it – the bamboo coral garden they are searching for. But what they see surprises everyone.

The screen is filled with white bamboo coral with pink polyps. It is clear it was not a garden but a bamboo coral reef. None of the ecologists on board have ever seen such high density of bamboo corals before. Meyer has encountered and sampled patches of the presumed coral species previously on a “nearby” seamount, Schulz Bank, during their first cruise on AMOR in 2018 (coordinates: 73.7945 N, 7.5072 E, Depth: 1029 m)  (https://doi.org/10.1016/j.dsr.2022.103920), but it was nothing in comparison to this. MAREANO project leader at the Institute of Marine Research, Pål Buhl-Mortensen, also on this cruise, previously documented higher than usual concentration of bamboo corals north of Svalbard before on a MAREANO cruise in 2022.

The bamboo coral is growing on top of its densely intertwined dead bamboo coral skeleton, similar to how the cold water scleractinian coral Desmophyllum pertusum grows on top its dead skeleton when it forms its reef. As far as all of the biologists onboard are aware of, bamboo coral does not typically grow on their dead coral framework like this. Eventually, the ROV approaches a hole in the reef, where the scientists watching the screen uses the lasers mounted on the ROV to estimate the thickness of the coral rubble, or dead coral skeleton, to be about 63 cm tall. They take a sample of the coral rubble and the bare sediment patch in between the mesh.

In the video room where the scientists are annotating the dive live with the institute’s newly updated live video annotating program, Seabed Field Observer (SFO), the first feeling is an overwhelming one. The biologists are recording the animals and presence of the habitat almost nonstop, identifying species on the spot and clicking away on their computers as the ROV continues along the reef. The area is filled with bamboo coral, ascidians, anemones, sponges, hydrozoans, bryozoans, gastropods, bivalves, decapods and the fish species Arctic rockling (Gaidropsarus argentatus) and Arctic Skate (Amblyraja hyperborea).

The biologists also start to notice juvenile skates and egg capsules along the dive. To Meyer, it indicates that the Arctic Skate species uses the area as a nursery ground, similar to what they observed on the summit sponge ground on Schulz Bank (https://doi.org/10.1016/j.dsr.2019.103137). Like here, the egg cases were lying on top of the biogenic material (made up of dead sponges instead of dead coral) that covers its summit completely. 

The bamboo coral reef is full of life, so much life that it is nearly impossible for a human brain to process and quantify it all at once – a job that requires specialist knowledge and intense focus. The only solace for those logging is when there are small patches of brittle star beds on muddy sand patches between the coral rubble or when the ROV stops to zoom in on the animals or take samples. The sheer density and 3D complexity of the bamboo coral reef and its skeleton intertwining within itself makes it almost impossible to see any of the smaller life living within the coral framework and only larger animals can be logged while the ROV is moving. After 3 hours, the scientists finally hear three magical words over the interphone – “end of line” – the ROV pilots are announcing the end of the dive. The biologists look at each other and take a common sigh of relief; their job is done and they can finally breathe. It is only then they fully realise the magnitude and beauty of what they just encountered. 

There is still much left to learn about the habitat and species that go with it. The extent of the reef exceeded the length of the 800 m long video line, and it is unclear how large the reef truly is. The small animals living within the framework could only be seen when Ægir6000’s 4K camera zoomed in on them, but how much life there is associated with the coral reef is not entirely clear. In addition, the exact bamboo coral species that dominate this site is currently unknown. To date, individuals seen in the video here and at Schulz Bank have only been identified to family level – Keratoisididae. However, it is hopeful that the samples of the living coral and its skeletal framework will help the biologists reduce that knowledge gap. Technology for deep-sea science has advanced greatly over the years and studying life at the bottom of the sea has become easier.