The deep sea coral Lophelia pertusa
Photo: NOAA Ocean Explorer (Wikipedia)

In the inky depths of the Gulf of Mexico, pearly white corals crisscross the seafloor, their translucent tentacles swaying to the current like flower petals on a midnight breeze. Lophelia pertusa brings life to what is often considered a cold, dead wasteland—and now, scientists are now bringing it back to the surface in the hopes that it help can restore dying coral reefs worldwide.

Lophelia, you see, has a superpower: It survives in waters too acidic for most other other corals, making it one of our best hopes for the future of reefs as rising carbon dioxide levels cause the oceans to acidify. Acid Horizon, a new documentary directed by Ivan Hürzeler, chronicles a scientific journey to gather specimens of this resilient creature and learn where its true limits lay.

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The hour-long film, which follows a 2014 research expedition into the Gulf of Mexico led by Temple University deep-sea biologist Erik Cordes, is a raw, real look at how science gets done. It juxtaposes the lofty ideas that drive scientists to plunge thousands of feet beneath the waves in metal cans (discovering the unknown! saving humanity!), with the seemingly endless barrage of technical difficulties that are part and parcel of field work.

Ultimately, it’s an uplifting tale, which is rare in an age when most news about corals centers on death and destruction. Through a series of harrowing dives with the famed Alvin submersible, Cordes and his companions are able to collect samples of Lophelia and bring it back to the surface intact. And through subsequent lab work—subjecting the corals to a battery of tests to determine their acid tolerance—they find the “super coral” they are looking for.

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“This is a coral that can live, and grow, and calcify, under the acid horizon,” Cordes told Earther, referring to the depth where the ocean becomes so acidic that corals’ calcium carbonate exoskeletons naturally start to dissolve. The hardiest of these corals, Cordes said, show resistance to pH values as low as 7.6—a level researchers believe the world’s oceans could reach by the end of the century. (The average pH of the oceans is currently about 8.1)

It’s been a few years since that fateful research expedition, and the work hasn’t stopped. Cordes has since returned to the Gulf to lead several additional research cruises, including the grim task of checking out damage from the Deepwater Horizon oil spill. Back in the lab, his team has continued to search for genetic markers that can explain Lophelia’s acid-tolerance, in addition to testing its ability to survive oil spills and elevated temperatures.

The ultimate hope is that Lophelia’s genetic secrets can be used to re-seed coral reefs being ravaged by humanity’s impacts. As a deepwater species that feeds on plankton instead of sunlight, Lophelia itself probably won’t migrate into the shallower depths where corals are now dying in droves due to heat-waves, pollution, and the creeping effects of ocean acidification.

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“But it gives us the hope there’s enough genetic variability out there that corals, in general, will make it through the worst of our effects,” Cordes told Earther. “And if we can unlock the secret to how the deepwater corals are doing this, there’s a lot of selective breeding and transplanting of corals starting to happen in shallow water” that could potentially benefit.

This past August, Cordes led a new research expedition aboard the R/V Atlantis to explore deep-sea ecosystems between Virginia and Georgia that are threatened by the Trump administration’s offshore drilling agenda. Not far off the coast of South Carolina, they came across an enormous Lophelia reef, about 85 miles in length, that hadn’t been documented before. They’ll be returning to the same coastline this spring to do more survey work.

“We’re trying to get in there first [before offshore drilling is expanded] and identify places that might be in need of protection,” Cordes explained.

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It’s the tension between humanity’s ever-increasing impact on the oceans and the hidden wonders beneath the waves that keep scientists like Cordes returning year after year. The acid horizon may be an alien world, but as the new film makes clear, it’s also a world worth fighting for.

Acid Horizon is available on iTunes and Amazon.

Update 11/25: Earther was originally informed that the cruise presented in the film took place in 2010. After publication the filmmakers clarified that it actually occurred in 2014. The article has been updated accordingly.

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