“Holly, which was put out of use in 2015, is one of 27 oil rigs built off the coast of California decades ago that have become hotbeds of biological activity. 

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.'”

From The Guardian.