Environmentalists and fishers want oil and gas structures in the ocean to be completely removed when they are no longer needed – but doing so could actually harm marine wildlife. Not only are deep-sea corals thriving on oil and gas rigs in the North Sea, the larvae they release may be helping repopulate damaged natural reefs elsewhere.

The cold-water coral Lophelia pertusa, which grows in the North Atlantic in waters deeper than 80 metres, can form vast …