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The climate crisis precipitated by our mindless fossil fuel consumption patterns is destroying coral reefs. Guess one place where corals seem to be thriving? Ironically, on oil rigs.
Warming oceans, low tides, and water pollution cause reefs to bleach and expel the algae that they need to survive – in so doing wiping away marine ecosystems that flourish near coral formations. But old oil-drilling infrastructures in the North Sea are often encrusted with deep-sea corals such as Lophelia pertusa, a cold-water reef-building coral that could help repopulate damaged natural reefs. Lophelia pertusa larvae use hard surfaces – like concrete – to settle upon, and after doing so they build huge reefs that are breeding grounds for redfish, ling and pollack, and full of little nooks and crannies for crabs and worms to settle into. Marine organisms like coral, bacteria, algae and sponges attract small fish, which then attract larger fish – creating a thriving community.

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This phenomenon has been observed already in the Gulf of Mexico, where countless bright corals have colonised the legs of 558 old oil rigs and gas platforms as part of a “Rigs-to-Reefs” programme. A typical eight-leg structure, reused as an artificial reef instead of being decommissioned on land, can provide a home for around 13,000 fish. Now researchers in the North Sea are planning to deploy artificial intelligence to better understand the effect oil rigs might have on sea life. In this way, authorities and oil companies alike might decide whether to take down ageing structures, or leave them in the sea as new ecosystems.
Environmentalists have long argued for oil and gas rigs to be removed from the sea and to return the seabed to its natural state. Man-made structures, often called “ocean sprawl”, can ruin natural habitats with sound, pollution and by attracting invasive species. More concretely, rigs nearing the end of their life must be removed from water according to the Oslo-Paris directive (OSPAR), which protects and conserves the North-East Atlantic. But what if more disruption was caused by decommissioning them?
Indeed, a growing library of literature suggests that removing structures can have adverse effects, as thousands of animals have chosen the artificial reefs that grow on them as their habitats. Individual rigs can become hotspots for biodiversity, acting as a refuge for marine life free to venture without the fear of fishing – which is forbidden within a 500 metre radius of any active oil and gas infrastructure. Some oil rigs and gas platforms in the North Sea were installed between 40 and 50 years ago, making them established parts of the ecosystem.
There are more than 1,300 energy-related structures in the North Sea, including wind turbines and underground cables, but the role of artificial habitats across the whole ecosystem is still poorly understood. Thomas Wilding, of the Scottish Association for Marine Science, says it is “relatively easy” to monitor individual structures, but researchers are now trying to understand the full picture.

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Scientists for INSITE – a dedicated programme looking at the ways man-made structures change the North Sea marine environment – are planning on leveraging cutting-edge technology to fill the existing knowledge gap. They say that this will help policy makers, companies and environmentalists make better decisions about what to do about man-made structures in the sea.
Wilding’s research, in partnership with Marine Scotland Science and the UK’s Department for Business, Energy and Industrial Strategy (BEIS), among others, is looking at the impact of putting structures in the sea as well as taking them out, as offshore renewable projects continue to be rolled-out. The three-year project, to start in April, aims at quantifying marine life and growth on structures, in order to predict what species grow in what environment. This will clarify the relationship between man-made structures and the ecosystems that depend on them, including animals that are commercially fished, or protected.
“We had some sort of semi-anecdotal evidence [that] there were lots of marine growth on these structures, but didn’t really fully appreciate how much and where it was located,” Wilding says. “That’s what we need to understand.”
The focus is on how old a structure is, where it is in the North Sea and at what depth reefs start to grow on it, and how this varies across different regions of the sea. Wilding hopes his research will also begin to reveal the overall impact of thousands of offshore renewables going in or hundreds of oil platforms coming out, which is currently unknown.

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Collecting this data is traditionally costly and time-consuming, but the rise of autonomous technology means it can now be done remotely. “The bottleneck in processing the imagery is no longer in collecting it, it’s in analysing it,” Wilding says.
Wilding and his team are set to identify what kinds of corals, algae and bacteria are growing on structures – and how much of it – using 3D imaging and machine learning. Maintenance footage taken by offshore operators reveals the true extent of coral, anemones and mussels on structures. Combining that footage with 3D-imaging, Wilding and his team will estimate the overall biomass of all the organisms dwelling on the structure, looking specifically at the bottom layer of growth.
That layer is made up of soft coral, oysters and clams, which play a critical role in the reef’s ecosystem as nourishment for bottom-feeding animals, and can reveal the overall health of the reef. Thousands of snapshots of marine life clinging to structures will also be annotated by Wilding and his team, then fed into an algorithm to automatically identify these species. This will over time develop into a monitoring tool for the industry. An ecosystem model will also predict how artificial reefs grow and change in specific conditions and what it means to remove structures fully, partially, or leave them in the sea.
These structures may not have been placed specifically at sea to tackle the loss of natural habitats, but these artificial reefs have nonetheless appeared as a byproduct of their presence. And in the case of the North Sea, so leaving structures in situ where corals are found could be key in fighting the loss of biodiversity, given that cold-water corals are fragile and slow-building.
There are other reasons to be pondering the removal of structures with some caution: the process costs billions and creates disturbances, including the release of trapped chemicals like diesel and hydrocarbons that are stored in drill cuttings – essentially debris from the drilling that sit on the seafloor for decades but can be shaken loose when a structure is removed.
What’s more, when a rig is carried ashore coated with corals, barnacles and all kinds of sea life, the whole ecosystem needs to be disposed of in specific ways. ”It’s technically a sort of hazardous waste, because it’s biological in origin,” Wilding says. “It costs a lot of money to landfill that material.” UK legislation allows operators to claim tax relief against hefty decommissioning bills, so the taxpayer covers some of this cost.
The Scottish Wildlife Trust is also campaigning for data-led decommissioning, asking the same questions as Wilding. It says that there are “potential triple-win scenarios from leaving oil and gas platforms in situ”: environmental benefits, and financial savings to the industry and to the taxpayer. The Trust proposes putting a percentage of money saved on decommissioning into a pot to fund marine research and conservation, which will help keep the industry accountable.
Granted: not every structure should be left to rot and rust at sea, says Sam Collin, who oversees policy and planning at the organisation. He thinks that new criteria should be introduced to prove a structure’s ecological importance: this would prevent companies from abandoning structures because it’s cheaper. He thinks that only inert materials like concrete should be allowed to stay submerged as they do not react to chemicals or decompose, while structures should also be cleaned of all pollutants like hydrocarbons and heavy metals.
“Our general feeling is that these structures are already acting as artificial reefs,” Collin says. “There’s interest in returning the seabed back to the state it was beforehand, but the North Sea has already been heavily impacted so that may not necessarily be the best option.”
“A lot of people don’t think about the structures themselves and the marine life growing on them, but there are diverse communities that exist there,” Collin says. “Because it’s generally associated with oil and gas, there’s a negative image.”
The OSPAR directive, which the UK is signed up to, generally prevents structures from being left in the sea, but Collin says that rules should be rethought in light of new data and that the UK should lead the change, looking at a structure’s potential as an artificial reef on a case-by-case basis.
“[The] oil and gas [industry] should take accountability for its impact on the marine environment but we have to be careful if that position ignores the potentially negative impact of decommissioning,” Collin says. “Our main interest is finding the best decision for the environment.”

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