Three hundred metres below the surface at Steigen, in Norway’s Nordland county, sunlight does not reach. Here grows Desmophyllum pertusum, a stony coral that lives without algae and feeds on what the current brings: phytoplankton, small crustaceans, particles. Until a few years ago it was called Lophelia pertusa. Large colonies add about seven millimetres a year. A colony can be centuries old, a reef thousands of years. Further north, in Lofoten, the Røst reef, built mainly of this coral, stretches for about 35 kilometres and is the largest known.
Salmon are farmed in the same fjords. To rid them of sea lice, small parasitic crustaceans, farmers use drugs. Emamectin benzoate reaches the fish in their feed. Azamethiphos, an organophosphate insecticide, and hydrogen peroxide are given as baths. The cage nets are coated with a recent antifouling agent, tralopyril, to stop algae and animals growing on them. Tralopyril carries a trifluoromethyl group, three fluorine atoms bound to one carbon, and so falls within the broad definition of PFAS adopted by the OECD in 2021. Some of each of these substances ends up in the sea. The question is what they do to the corals.

The VDWS Transition project, led by Norway’s Institute of Marine Research (IMR), set out to answer it. It is funded by FHF, a company owned by the Norwegian Ministry of Trade, Industry and Fisheries and financed by a levy on seafood exports. At Nord University, PhD candidate Birte Katarina Schuppe and her supervisor, Henning Reiss, collected live colonies in nearby fjords, at Steigen from about three hundred metres, and brought them to the tanks of their research station. They exposed them first to emamectin, then to azamethiphos and tralopyril. They photographed the corals every two minutes, day and night, to follow tentacles and mucus. They sealed them in measuring chambers to record oxygen consumed and ammonium excreted. They froze fragments and sent them to IMR to look for the drugs in the tissue.
The emamectin results are in the project’s final report, published by IMR on 9 March and updated on 21 August. Adults exposed to 0.129 and 0.596 milligrams per litre accumulated the drug in their tissue. They consumed more oxygen, released more ammonium and produced more mucus. Some polyps died, especially at the higher dose. For azamethiphos and tralopyril in adults, no data have yet been released.

Those doses, however, are not found at sea. In 2024 an IMR team exposed another seabed animal, the sea pen Pennatula phosphorea, to 0.8 milligrams per litre of emamectin for eight days, and set out the comparison with the sea in writing. Near farms, a model puts concentrations at around four thousandths of a nanogram per litre, and field measurements stay below the detection limit of 0.25 nanograms per litre. The lower dose given to the corals, 129,000 nanograms per litre, exceeds that limit more than five hundred thousand times. Emamectin also reaches the seabed mainly bound to settling particles, not dissolved in water. The sea pen showed no change in behaviour or metabolism, but retained the drug in its tissue for at least six days. The risk those authors saw was build-up after repeated treatments.

Emamectin benzoate: the two doses used on adult Desmophyllum pertusum in the VDWS Transition experiment, compared with the detection limit of water measurements near fish farms and the model estimate reported by Taormina and colleagues (2024). Log scale. Chart produced by Scienzaonline from data in Dunlop K.M. et al., Rapport fra havforskningen 2026-14 (IMR, 2026), and Taormina B. et al., Marine Pollution Bulletin 198, 115903 (2024), doi 10.1016/j.marpolbul.2023.115903
The most sensitive finding concerns the larvae. Those of Desmophyllum proved highly sensitive to hydrogen peroxide: half die at 27.2 milligrams per litre. They are more sensitive still to azamethiphos. Half show effects at 1.89 micrograms per litre, less than two millionths of a gram. Hence the report’s recommendation: where the coral grows within one kilometre of a farm, no hydrogen peroxide and no azamethiphos in spring, the spawning season.

The report also looks at the everyday risk, the organic matter falling from the cages: faeces and uneaten feed. In two deep-water gorgonians, Primnoa resedaeformis and Paragorgia arborea, tissue degrades where accumulated sediment exceeds one or two thousand grams per square metre, at distances between 10 and 600 metres from the cages depending on species and current. The authors propose dropping the circular buffer zones drawn around farms in favour of high-resolution current models, because material settles downstream, not in a ring. For Desmophyllum, however, the sample was too small to estimate its sensitivity to organic matter. That is the most serious limitation in the report: the reef-building species is the one least understood.

Norway holds between 25 and 50 per cent of the European population of this coral and between 5 and 25 per cent of the global one, according to the Norwegian Red List of 2021. The same assessment lists the species as near threatened and names bottom trawling as the main threat. Between 30 and 50 per cent of reefs off the Norwegian coast bear physical damage from nets.
The Mediterranean has its own deep white corals. Off Santa Maria di Leuca, in the Ionian Sea at the heel of Italy, live colonies of Madrepora oculata and Desmophyllum pertusum grow between 425 and 1,100 metres, the most extensive and deepest known deep-sea coral community in the Mediterranean. Fish farms play no part there. Underwater footage analysed by D’Onghia and colleagues, published in 2017, showed longlines tangled in the corals, scars left by trawl doors and, above all, plastic, most frequent precisely where the corals grow. Since 2006 the area has been a Fisheries Restricted Area under the General Fisheries Commission for the Mediterranean, which bans trawls and dredges. According to the study, trawling still weighs more than longlines.
At Steigen, analysis of the frozen fragments will show whether the corals actually take up azamethiphos and tralopyril, and with what effect. For now the fragile stage is the larva, and the report protects it with a rule of the calendar. The effects on adults, seen in tanks at high doses, say nothing yet about the sea. And Norway’s reefs, outside the tanks, carry the marks of nets.

References
Dunlop Katherine Mary, Da Silva Gomes Ana Cristina, Laroche Olivier, Järnegren Johanna, Meier Sonnich, Sævik Pål Næverlid, Schuppe Birte Katarina, Reiss Henning et al. (23 authors), “Metoder for å vurdere følsomheten til forvaltningsrelevante bunnarter overfor akvakulturaktiviteter”, Rapport fra havforskningen 2026-14, Havforskningsinstituttet, 9 March 2026, updated 21 August 2026. ISSN 1893-4536. https://www.hi.no/hi/nettrapporter/rapport-fra-havforskningen-2026-14
Nord universitet, “Korleis vert korallar påverka av kjemikaliar frå oppdrettsnæringa?”, 8 May 2026. https://www.nord.no/aktuelt/korleis-vert-korallar-paverka-av-kjemikaliar-fra-oppdrettsnaeringa
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Addamo A.M., Vertino A., Stolarski J., García-Jiménez R., Taviani M., Machordom A., “Merging scleractinian genera: the overwhelming genetic similarity between solitary Desmophyllum and colonial Lophelia”, BMC Evolutionary Biology, 16, 108, 18 May 2016. doi: 10.1186/s12862-016-0654-8
Artsdatabanken, “Desmophyllum pertusum”, Norsk rødliste for arter 2021. https://lister.artsdatabanken.no/rodlisteforarter/2021/5718
D’Onghia G., Calculli C., Capezzuto F., Carlucci R., Carluccio A., Grehan A. et al., “Anthropogenic impact in the Santa Maria di Leuca cold-water coral province (Mediterranean Sea): Observations and conservation straits”, Deep Sea Research Part II: Topical Studies in Oceanography, 145, 87–101, 2017. doi: 10.1016/j.dsr2.2016.02.012
Regjeringen.no, “Fiskeri- og havbruksnæringens forskningsfinansiering (FHF)”, Ministry of Trade, Industry and Fisheries. https://www.regjeringen.no/en/dep/nfd/organisation/etater-og-virksomheter-under-narings--og-fiskeridepartementet/selskaper/the-fishery-and-aquaculture-industry-res/id168263/