- A new study published in the journal Marine Biodiversity delivers the first global IUCN Red List assessments for 22 cold-water coral species in the Northeast Atlantic.
- More than 30% of the species are at risk of extinction due to bottom-contact fishing, habitat destruction and climate change, with white coral (Desmophyllum pertusum) listed as globally vulnerable.
- Experts say the findings highlight gaps in conservation, especially for deep-sea species often excluded from monitoring and protection efforts.
- The study’s release comes at a key moment, as international talks continue under the Beyond National Jurisdiction Treaty to improve high seas biodiversity protections.
They live in the ocean’s coldest, darkest depths, far from sight — but cold-water corals are far from safe.
In a first-of-its-kind study published in Marine Biodiversity in June, a team of researchers led by Julia Sigwart of Germany’s Senckenberg Research Institute assessed the global extinction risk of 22 cold-water coral species in the Northeast Atlantic.
Using the Red List criteria of the International Union for Conservation of Nature (IUCN), the world’s authority on extinction risk, they found that more than 30% of these species are now globally near threatened or vulnerable — including white coral (Desmophyllum pertusum), a stony, reef-building coral.
The study also highlights that the population health of several of the Northeast Atlantic deep-sea coral species considered in the study haven’t been evaluated by the IUCN yet — leaving conservation gaps wide open.
“The fact that > 30% of the species we assessed are facing an elevated estimated risk for global extinction,” the authors write, “is a sobering reflection of the extreme destruction of deep-sea habitats, which so often goes unnoticed.”
Long-overdue attention to life in the deep
Despite their ecological importance, deep-sea corals have largely been left out of global extinction risk assessments.
“The lack of assessments for cold-water corals was an obvious gap in the coverage of the IUCN Red List,” Sigwart, head of malacology at Senckenberg, told Mongabay. “Marine species, especially deep-sea benthic ones, are under-represented — and that leaves open an assumption that everything is fine.”
To help fill that gap, her team assessed 22 species found in the Northeast Atlantic, home to some of the best-studied cold-water coral habitats. These included reef-forming stony corals as well as soft-bodied species like sea pens and gorgonians. The selected species all had well-documented biology, clear taxonomy, and broad geographic ranges.
Still, a broad range didn’t shield them from risk. “Documented large-scale declines of widespread species clearly demonstrate the magnitude of threats to deep-sea ecosystems,” the team writes.
Most assessments were based on IUCN Red List Criterion A, which measures population decline, often using habitat degradation as a stand-in when direct data are lacking.
David Obura, co-chair of the IUCN’s Coral Specialist Group, who wasn’t involved in the study, backed the approach. “Criterion A uses proxies like habitat availability to supplement limited abundance data,” he told Mongabay. “The assumptions are tested and strengthened in all applications — and the team has done this well for cold-water corals.”
Destructive fishing and a warming ocean
Bottom-contact fishing, like deep-sea trawling and dredging, has emerged as the top threat, according to the study’s authors. “These can cause massive damage to the benthos,” Sigwart said, referring to life on or near the seafloor. “Corals, even sea pens, have hard skeletons that are broken by the impacts from these types of fishing gear.”
The most striking case is white coral, found mainly across the North Atlantic. Its towering reefs shelter countless marine species. Yet researchers estimate its global population has dropped by more than 30% in the past century due to trawl fishing. “This is really a staggering level of damage,” Sigwart said.
And worse may be coming: in worst-case scenarios, suitable habitat for white coral in the Northeast Atlantic could shrink by 85% due to warming and acidifying oceans. Even where the species is well studied, like the U.K. and Ireland, large portions of its habitat remain unprotected. Across the Northeast Atlantic, more than 70% of known reefs fall outside marine protected areas.
Sea pens, like the tall sea pen (Funiculina quadrangularis), also show signs of sharp decline. Recognized by its square-shaped skeleton, F. quadrangularis was once widespread across parts of the Atlantic but is now rare in areas where it was frequently caught as bycatch.
“Sea pen habitats are … threatened by fishing activity,” the study says, “and must be better understood and protected considering their role as habitat for other species, including fish larvae and juveniles.”
Three coral species — Anthoptilum murrayi, Balticina christii and Convexella jungerseni — were labeled data deficient, meaning there’s not enough information to assess their status. But that doesn’t mean they’re safe. “There is often a hint that the species is in decline,” Sigwart said, “or perhaps evidence that it is in trouble in one part of its range, but not enough data to estimate the impacts on the global population.”
A turning point for deep-sea conservation?
This first wave of global Red List assessments for cold-water corals lays critical groundwork for improving species-level conservation, especially in the largely unregulated high seas.
“All policy processes must be informed by science, even where the science may be preliminary or limited,” Obura said. “The findings show that deep-sea species, in spite of the size and depth of the ocean … are being impacted by human activities to the point of making them threatened with extinction.”
He said the findings come at a key moment, with the pending ratification of the Biodiversity Beyond National Jurisdiction Treaty, a global pact to protect marine biodiversity in international waters. “Using these results to prevent the threat status of all these species increasing … can provide critical indicators for effective regulation in international waters,” Obura said.
So far, most protections have focused on habitats, such as those designated as marine protected areas, vulnerable marine areas, and fisheries management zones. The European Union’s 2017 ban on bottom trawling below 800 meters (about 2,600 feet) was a major step in the right direction, conservationists say. But many corals, especially those in shallower waters or the high seas, remain outside protected zones.
“The Red List offers an important complementarity to recognise how threats impact individual species in different ways,” the study notes.
Still, challenges remain in expanding conservation efforts. Deep-sea fieldwork is expensive and logistically complex, often relying on remote-operated vehicles or seabed imaging. But many coral species can’t be reliably identified from photos alone. “Image data are usually insufficient for species identification,” the researchers write, highlighting the need for expert taxonomic input and specimen-based surveys.
Monitoring also needs to improve. “It is not enough to just go look at an area one time,” Sigwart said. “It’s essential … to track patterns in species abundance and distribution over time.”
The team said this is a crucial first step. “This work provides a starting point,” they wrote. “Further work on [cold-water coral] assessment is clearly urgently needed, as is a better understanding of their biology and ecology.”
Banner image: A brittle star (Gorgonocephalus sp.), recognizable by its numerous abundantly branched arms, attached to a white coral (Desmophyllum pertusum). Image by Ifremer via Wikimedia Commons (CC BY 4.0).
Citation:
Sigwart, J. D., Allcock, A. L., Mikosz Arantes, R. C., Barnhill, K. A., Bax, N., Beneti, J. S., … De Wilt, M. E. (2025). The first IUCN Red List of cold-water corals highlights global declines. Marine Biodiversity, 55(3), 51. doi:10.1007/s12526-025-01533-0
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