An oil rig that environmentalists love? Here’s the real story.

In 1984, eight miles off the coast of Southern California, the 700-foot tall oil platform, Eureka, was anchored into the depths of the Pacific.

For four decades, amidst the constant humming of oil extraction, millions of invertebrates began to cling to the pilings beneath the surface, initiating an ecosystem of their own.

Eureka soon became an ironic juxtaposition: a massive industrial structure encrusted with vibrant sea life. An endless field of strawberry anemones started to line the rig's industrial beams, and crustaceans tucked themselves into the dense labyrinth of mussels. Now, cormorants plunge through the surface, and dozens of sea lions dip down from the structures above the water, gliding through the plentiful schools of fish that roam below.

“Every square inch is covered in marine life,” says Milton Love, biologist at the Marine Science Institute at University of California, Santa Barbara. “Sometimes there are so many fish that you can’t even see through them to the platform. It’s overwhelmingly striking.”

This marine hot spot is one of 23 oil rigs and pipelines off the coast of California, fifteen of which are active, like Eureka. Constructed between 1967 and 1989, these rigs are nearing the end of their lifespan. With production levels declining, what to do with the rigs when they are no longer economical remains a quandary: Should oil companies remove the rigs, taking the reefs with them? Or should the rigs remain, leaving the ecosystem in an unnatural state?

What makes Eureka particularly controversial isn’t just the bounty of marine life, it’s that, according to Love’s research published by the Proceedings of the National Academy of Sciences in 2014, the platform habitat is even more productive than some natural reefs—hosting a thriving ecosystem that still exists today.

“If you remove a platform, you may be killing tens of millions of animals because they happened to settle on steel instead of a rock,” notes Love, “Which I think is a tragedy.”

The platforms’ abundance is due to both its location as well as its idiosyncratic design. Unlike other oil platforms, Eureka’s complex shape offers hiding spots for marine life, and access to a consistent flow of cold currents that bring in more species.

Where most rigs have vertical, cylindrical pilings, Eureka has layer-upon-layer of flat skirt pilings, which replicate the sea floor at various depths throughout the entire water column.

Love notes that most of the fish around the platform likely drifted over with the currents early in their lives, finding themselves at the rig when they needed something hard to settle onto.

Near the surface, where a great deal of photosynthesis occurs, those young fish can feed on plankton, and on the pilings, they can pick off crustaceans and arthropods living among the anemones.

“Eureka is by far the most productive of the platforms off of California,” says Jeremy Claisse, who co-wrote the paper with Love. “It’s as productive as any other marine fish habitat that has been studied around the world.”

As fish get older, they tend to slowly move deeper down the platform, where light steadily dims, and where the species multiply both in size and quantity. Deepwater corals extend off the pilings like branching trees, and shoals of striped rockfish that make up roughly 90 percent of the species of fish associated with the platform’s habitat.

Claisse and Love mention that while many natural structures, such as mountain-shaped pinnacle reefs, similarly support marine life, the scale is nowhere near that of Eureka.

“Even those don't have this sort of open space between the structures that Eureka has,” continues Claisse. “It’s a really weird, productive and unique place.”

By 2055, most of California’s 23 offshore oil platforms are expected to cease operation. When oil companies constructed the rigs, they assumed responsibility for dismantling, or decommissioning, each of them. However, the unanticipated sea life has many officials reconsidering whether the rigs should be dismantled at all.

Recent California oil spills—like the 25,000 gallons that leaked from a broken pipeline connected to a rig—have left many environmental groups wary of any oil infrastructure, regardless of whether it’s actually pumping oil. With eight of the 23 rigs no longer producing oil and set to be decommissioned within the next few years, time to reach an agreement is running out.

Some want oil companies to completely remove platforms, restoring the marine environment to its natural condition. Others want the rigs converted into protected, artificial reefs, saying that dismantling the rig would sabotage an abundant ecosystem.

The complex and costly process of full decommissioning involves plugging and cementing wells before completely removing the entire structure. However, some are opting for what is called partial decommissioning: where only the upper section of the rig is taken down to a depth of approximately 85 feet, to eliminate any hazards to ship hulls. The remaining lower portion would be left as a sanctuary for marine life, designated by the U.S. Department of Interior’s Rigs-to-Reef program, and a destination for recreational diving and fishing.

However, Linda Krop, chief counsel for the Environmental Defense Center, says leaving the rig in place could leave toxins in the environment—a concern she currently has about huge debris mounds that remain on the seafloor from platforms removed thirty years ago.

“Right now, toxic materials like arsenic and lead aren’t being leaked into the marine environment, but they could be disrupted by things like an earthquake, seismic activity, or human-caused disruption, like getting snagged in fishing gear,” she says.

Krop also notes that, when it comes to what’s truly best for the ecosystem, scientists have to consider many factors, not just wildlife populations. She worries the abundant fish may attract recreational fishing, limiting the rig’s environmental benefit by reducing fish populations.

Claisse mentions that while some recent studies conducted at the California rigs have shown no higher levels of heavy metals in the species associated with the platforms, marine environments near industrial complexes are often infused with harmful components. He adds that more research to be done to understand industrial toxins.

“Not every oil platform is a good candidate for an artificial reef,” says marine conservation biologist Emily Hazelwood, co-founder of the environmental consulting firm Blue Latitudes. “You need to do extensive biological surveying to understand the value [of each] and what marine life is there.”

But she thinks Eureka is a good candidate, given the wide variety of species living there and its potential to harbor endangered species. With the help of an ROV, Hazelwood and her co-founder Amber Sparks found that an iconic starfish species, the Giant Pacific Sunflower, was flourishing.

Currently, the sea stars are classified as Critically Endangered on the International Union for the Conservation of Nature (IUCN) Red List. Since 2013, 90 percent of the sea star’s population has been lost to disease caused by increasing temperatures and acidification.

“They had a massive die-off and are really hard to find now, but we found them.” says Hazelwood.

What becomes of Eureka may even set a precedent for new energy infrastructure. Claisse notes that Eureka’s environmental research is being applied to designs for other structures, such as offshore wind.

He adds, “No one intended for these oil platforms to be fish habitats, but looking forward, [we have to ask] in what ways can we think about making anything that we put in the ocean habitual, if they’re going to be out there anyway?”