Offshore infrastructure finds new life as reef habitat

Thousands of offshore oil and gas platforms, as well as oceanic wind turbines, will be decommissioned in the coming decades as they reach the end of their working lives. Under current global regulations, most decommissioned rigs will be completely removed from marine environments the world over at an estimated cost of $210 billion US.

But what if there was a compelling ecological argument for leaving decommissioned rigs where they are?

A study led by Jonas Teilmann of Aarhus University in Denmark, published last week in Frontiers in Ecology and the Environment, argues that environmental agencies around the world should rethink the expensive strategy of hauling rigs, turbines and other industrial energy infrastructure from marine environments when they’re worn out.

“We have observed a significantly increased biodiversity around the old facilities,” Teilmann said in a release, a sentiment echoed by more than 200 experts from academia and government who joined in the study.

In the North Sea, a waterbody stretching from the United Kingdom to Germany, Denmark and Norway, 1,350 such marine platforms are currently installed. Via a submerged camera, Teilmann and his team found old oil rigs serving as home to flatfish, cod and numerous forms of bottom fauna.

“An old oil rig will have the same function as a natural stone reef,” Teilmann wrote. “We also see many more porpoises around oil rigs than in the surrounding sea. It’s easy to understand why the porpoises enjoy the area. One can’t throw a fish hook without catching one of the many cod around the legs of the oil rig.”

‘Flexible’ approach urged

Of the 200 experts surveyed, 94.7 per cent recommend governments take a more flexible approach to their individual decommissioning policies. Most preferred partial removal to completely uprooting the established structures, though many suggested any decision for how to treat old energy hardware should be based on an environmental assessment. Important considerations included local biodiversity, provision of reef habitat, relative energy use and the feasibility of recycling the removed structures.

"One can’t throw a fish hook without catching one of the many cod around the legs of the oil rig."

To be sure, there are risks associated with partial removal, yet Teilmann’s team believe the potential impacts of complete removal are more damaging, including the loss of already established reef ecosystems, seabed disturbance and the re-opening of no-fishing areas to trawling activity.  

Rig-to-reef

Ashley Fowler, a researcher with the University of Technology in Sydney, Australia and a co-author of the study, noted the argument in favour of removing old energy infrastructure from the sea is based on an idea of “leaving the seabed as you found it” as a way of “minimiz[ing] negative impacts on the marine environment.”

But the trend towards leaving decommissioned rigs in place is gaining momentum. In the United States, rig-to-reef options are already in place, and practices like sinking decommissioned ships to become artificial reefs is finding broad acceptance.

Today, scientists like Teilmann believe that leaving greater numbers of offshore installments in place can provide a net gain in marine habitat that function as gathering places for marine life. And though habitat provided by offshore infrastructure is miniscule compared to that of natural hard substrate, the installments still provide substantial benefits to North Sea ecosystems.

Their findings also support the growing global concern over the environmental risks of sea-based infrastructure removal, everything from the loss of no-fishing zones to habitat loss and marine life disruption. Opening an existing off-limits area to deep sea trawling would “turn the seabed into a uniform desert with poor biodiversity,” Teilmann argues.

The team have developed a series of recommendations to assist in the revision of decommissioning policy. They suggest governments halt all obligatory rig removals to allow researchers an opportunity to study what ecosystem niches are provided by sunken offshore infrastructure to better create habitat and protect the flora and fauna who call the abandoned detritus of human life home.