Story by Lina Chowdhury Duffy, KLN ’25
Illustration by Hallie Thornton, TYL ’12
Images from Erik Cordes and ROV SuBastian / Schmidt Ocean Institute
Mapping the deep ocean begins in a way that surprises most people: by driving a research vessel slowly back and forth across the water.
“You cannot map the seafloor with satellites,” Temple University Biology Professor Erik Cordes says. “You have to take a ship out and drive over every square mile.” Each line of sonar becomes another thin stripe on the screen, revealing reefs and habitats that have never been documented. The deep ocean is the planet’s largest living system and its least understood. It begins where sunlight fades out entirely, thousands of feet below the surface, in a realm defined by cold temperatures, intense pressure and ecosystems adapted to near-total darkness. Stretching across nearly 60% of Earth’s surface and making up 95% of the planet’s available living space, it stores carbon, regulates climate and supports the global food web. Yet as industrial activity moves into deeper waters, the ecosystems that sustain those functions remain largely unmapped and unprotected.
Cordes has spent more than two decades studying deep-sea environments. His work asks a deceptively simple question with global implications: How do we explore and benefit from the ocean’s resources without destroying the systems that make them possible? “Most people will never see the deep sea,” Cordes says, “but it affects every one of us. It keeps carbon out of the atmosphere, supports our fisheries and shapes the planet’s climate.”
Cordes’ lab at Temple is one of the few in the world focused on both the science and stewardship of deep-sea ecosystems. His team uses seafloor mapping, predictive models and submersible surveys to locate and study coral communities thousands of feet below the surface. They are documenting biodiversity in uncharted regions, testing artificial coral structures to restore damaged reefs, and advising international agencies and foreign governments on how to manage deep-sea resources responsibly.
Erik Cordes leads numerous deep-sea expeditions, including a remotely operated vehicle dive on board the EV Nautilus research vessel. Image courtesy of Alex DiCiccio.
Understanding the deep-sea engine
When Cordes describes the deep sea, he calls it “the engine you cannot see.”
Organic material constantly rains down from the surface in what scientists call marine snow. On continental slopes and plateaus, that material settles onto coral structures that have been growing for centuries or even millennia. Those coral communities transform waste, recycling nutrients that eventually return to the upper ocean—the sunlit, biologically productive layer where most marine life and fisheries are concentrated—and feed the fisheries that coastal economies depend on.
In 2018 and 2019, Cordes and a team of collaborators discovered a 200-mile-long coral reef on the Blake Plateau, off the Carolinas along the U.S. East Coast. “You would think we’d already explored that area,” he says. “But that’s how little we know. We are still mapping these massive reef systems we didn’t know existed.”
Those reefs, located beneath the Gulf Stream, do more than shelter deep-sea life. They help maintain the productivity of surface ecosystems. “A reef is part of the engine that feeds people,” Cordes explains. “It keeps food on our plates and carbon out of the air.”
Deep-sea corals also play a vital role in long-term carbon storage. Their skeletons lock carbon in for thousands of years, and the surrounding organisms keep additional carbon trapped at depth rather than cycling it back into the atmosphere. Losing those systems, Cordes says, would weaken one of the planet’s natural climate regulators: “A lot of the carbon and heat we’re generating ends up in the ocean. The deep sea is preventing our planet from overheating worse than it already is.”
Erik Cordes also educates others beyond the academic community, teaching a course on science communication and collaborating with artists, filmmakers and musicians to make deep-sea research more accessible.
Erik Cordes’ team documents biodiversity in uncharted regions, tests artificial coral structures to restore damaged reefs, and advises global agencies and foreign governments on how to responsibly manage deep-sea resources.
From disaster to restoration
Cordes was part of the scientific effort that followed the 2010 Deepwater Horizon oil spill. His research off the coast of Louisiana, where he had been studying deep-sea ecosystems for years, contributed to understanding how those environments responded and what restoration might require.
“We were already working in the Gulf at the time of the spill,” he recalls. “After Deepwater Horizon, we became involved in the deep-sea assessment work, and that eventually moved into restoration—looking at what these communities needed to recover and what was even possible at that depth.”
“We’re finding extraordinary things down there. But if we lose those habitats before we understand them, we won’t even know what we’ve lost.”
—Erik Cordes
Professor of biology
Until then, restoration was largely confined to shallow or coastal waters. “It’s really never been done in the deep sea,” Cordes says. “We’re borrowing ideas from shallow-water restoration, but it’s a very different world down there.”
At depths beyond 3,000 feet, corals cannot survive under normal atmospheric pressure. Traditional restoration methods—growing coral fragments in nurseries and transplanting them—do not work. “We tried that a little bit,” he says, “but the success rate wasn’t high. You get to a point where you’re removing more corals than you’re putting back, and then you become part of the problem instead of part of the solution.”
Instead, Cordes’ team began developing artificial reefs in the lab using 3D printing.
“We cast them into different forms and put them out to mimic what the real corals were doing in the environment,” he explains.
Exploration and governance
Only about 30% of the seafloor has been mapped at high resolution, leaving large areas of deep water essentially unknown. Cordes’ team builds predictive models from the maps that do exist to identify where deep-sea corals are likely to occur.
“We can predict where they’re going to appear,” he explains. “That helps us find new reefs at the bottom of the ocean and guide our dives.”
That same need for baseline information underpinned his partnership with scientists in Argentina, where his team helped expand deep-sea research capacity. Supported by the Schmidt Ocean Institute and the Coral Research and Development Accelerator Program, the team is surveying deep waters off the Argentine coast and training local researchers in seafloor mapping, species identification and remotely operated vehicle operations.
The work reflects a broader need he sees worldwide: building scientific baselines before offshore development accelerates. In Colombia, Cordes participated in a workshop organized by the Deep Ocean Stewardship Initiative and its Offshore Energy Working Group, which he founded in 2015. The goal was to advise the Colombian government on managing its expanding oil and gas activity in the Caribbean and its potential move into the Pacific. The discussions brought together representatives from the Colombian government and local universities.
“Development is starting to move into deeper water,” he says. “We’re helping them think about how to manage their offshore resources before industry moves in.”
A remotely operated vehicle exploring and mapping the seafloor off the Pacific coast of Costa Rica reveals a group of scabbardfish schooling.
Mapping the deep ocean starts by driving a research vessel slowly back and forth across the water.
Science with purpose
Cordes also devotes significant effort to communicating science beyond the academic community. He teaches a course on science communication and collaborates with artists, filmmakers and musicians to make deep-sea research more accessible.
During the Argentina expedition, the Schmidt Ocean Institute livestreamed the dives online. One of the dives garnered over a million viewers, allowing people around the world to watch the discoveries in real time. “People were saying, ‘This is what happens when you fund science.’ It became a national moment,” he says. “When people can see what’s down there, they start to care. It builds public understanding and political will.”
Recently, his lab partnered on a sculpture and augmented-reality installation at the entrance of Temple University’s Bio-Life Building, which lets visitors experience a coral reef through both sight and sound.
“We want people to understand that it’s not an empty space. It’s full of life, and it’s connected to everything we depend on.”
—Erik Cordes
Professor of biology
Building predictive models to identify where deep-sea corals are likely to occur, Erik Cordes’ team finds a coral reef at 800 m depth on the side of an atoll in the Phoenix Islands.
A QR code allows visitors to look through their phones and see fish swimming through the sculpture, hear the sounds of the deep ocean and see particles of marine snow falling. “It’s a way to bring the deep sea to people who will never get to go there,” he explains. “We want people to understand that it’s not an empty space. It’s full of life, and it’s connected to everything we depend on.” At Temple, Cordes’ work contributes to a growing research focus on sustainability and environmental resilience. Through field expeditions, restoration studies and international collaborations, his lab is helping build the scientific foundation needed to guide policy decisions before industrial pressures reach sensitive ecosystems. The work also gives students— from undergraduates and graduate students to postdoctoral researchers—hands-on experience with one of the planet’s most complex environmental challenges.
“We’re finding extraordinary things down there,” he says. “But if we lose those habitats before we understand them, we won’t even know what we’ve lost.”