Deep sea discoveries never fail to amaze me, and this one of a coral that lives on metal deposits is extra special.
I love Ocean News from the National Oceanography Centre for the diversity of awe-inspiring front-line ocean research and discovery.
This week the top story reports on the discovery of tiny deep-sea corals thriving on slow-growing metal-rich rocks 4000 meters below the surface in the Pacific. A picture of Deltocyathus zoemetallicus shows a beautiful goblet-shaped polyp on a dark bolder.
This stony coral lives in total darkness and forms a hard skeleton of calcium carbonate at a depth where calcium carbonate is present at concentrations below saturation. Here, calcium carbonate should dissolve, not precipitate into hard corals. This means Deltocyathus zoemetallicus must be specially adapted to maintain hard skeletons in good condition.
Another environment where calcium carbonate is increasingly difficult to precipitate is our (future) surface ocean. The continuous rise in atmospheric carbon dioxide concentrations result in more carbon dioxide equilibrating with the surface ocean, leading to the acidification of surface waters. In turn, this increases the solubility of calcium carbonate and as a consequence, marine life, such as planktonic algae, mollusks and corals will increasingly struggle to build and maintain their skeletons and shells. Perhaps there is something we can learn from the dwellersof the deep.
Polymetallic accretions, or nodules, grow at a slow pace – a few millimeters over thousands of years – and are the focus of increasing interest in deep-sea mining. We (our society) want these nodules to feed our insatiable appetite for ‘stuff’ (mobile phones, vapes, laptops, TVs, batteries, cars, christmas decorations…). Yet if we loose these fields of polymetallic nodules in the deep, they will not re-grow in a meaningful time scale. What we potentially loose with them is an ecosystem of rich biodiversity we don’t yet know much about, let alone its role in the life-sustaining system that is our ocean.
Those potatoe-sized nodules in the deep contain a range of metals, including lithium, manganese, copper, iron, nickel, cobalt and rare earth elements, some of which are on one hand essential for life and on the other potentially toxic. Some 600 species of animals, including brittle stars, soft corals and sponges have been found to thrive on and around them, somehow dealing with high metal concentrations in addition to other (to us) hostile conditions, such as absolute darkness and high pressure. One clue may be that polymetallic nodules are involved in seawater electrolysis, producing ‘dark oxygen‘, perhaps one contribution to sustaining life in the deep and enticing a species of octopod to lay her eggs exclusively onto sponges that grow on manganese nodules. What a fascinating interplay between chemistry and biology exists below 4000 m depth. In my world, it is worth preserving!
So keep your gadgets for another year or three, buy second hand where possible, minimise waste and make sure recycling is the destination of your remaining waste. Perhaps those actions can lessen our hunger for destroying deep-sea environments.
Original publication reference:
Guadalupe Bribiesca-Contreras, Nadia Santodomingo et al., Hidden gems of the abyss: first species of azooxanthellate scleractinian coral (Scleractinia: Deltocyathidae) attached to polymetallic nodules in the eastern Pacific Ocean, Zoological Journal of the Linnean Society, Volume 205, Issue 3, November 2025
https://doi.org/10.1093/zoolinnean/zlaf146
Images:
Featured image and Scleractinia: Deltocyathidae from original publication reference given above (https://doi.org/10.1093/zoolinnean/zlaf146)
Deep-sea octopod: New octopod species near Kaʻena Ridge, Hawaiʻi, observed in 2011. (credit: Woods Hole Oceanographic Institute and the University of Hawaiʻi)
Manganese nodule: “Pelagite (deep seafloor manganese nodule) (Pacific Ocean) 1” by James St. John is licensed under CC BY 2.0.
Challenging Habitat 