While not natural structures, their platforms have been embedded into the muddy seabed long enough to become part of the ocean environment, providing a home for creatures like mussels and barnacles, which in turn attract larger fish and sea lions that find safety and food there.

After two and a half decades of studying the rigs, Bull says it’s clear to her: “These places are extremely productive, both for commercial and recreational fisheries and for invertebrates.”

Now, as California and the US shift away from offshore drilling and toward greener energy, a debate is mounting over their future. On one side are those who argue disused rigs are an environmental blight and should be removed entirely. On the other side are people, many of them scientists, who say we should embrace these accidental oases and that removing the structures is morally wrong. In other parts of the world, oil rigs have successfully become artificial reefs, in a policy known as rigs to reefs.