In high seas, scientists see a lifeline for coral reefs

The vast, underexplored seas covering much of the planet could be the key to saving what remains of a more familiar undersea feature, a new study finds. The “living rock” that thrives in tropical shallows around the world, coral supports a quarter of all marine life. Yet around 20 percent of the world’s coral is already gone, and most of the rest is severely threatened by climate breakdown, overfishing and pollution.

Now, a deep dive into history on the “high seas” — the waters that lie beyond maritime borders — is providing a ray of hope for the world’s reefs: Combing through historical data and more than half a million records on the distribution of corals worldwide, researchers identified more than 116 coral reefs flourishing throughout the high seas.

Conservation News spoke to the study’s lead author, Daniel Wagner, a marine scientist at Conservation International, about the scientific allure of the high seas and what this discovery could mean for the world’s dying reefs.

Question: Why is this discovery so important?

Answer: Most people perceive the high seas as an ocean desert: barren, lifeless and mysterious. This study shows that the high seas are more than just the blue carpet of nothingness that you see from an airplane window. After compiling and analyzing coral reef records from a range of sources — including museum collections, underwater surveys and scientific databases — we discovered an array of marine life teeming below the surface of this unexplored region of the ocean.

Specifically, our study looked for “reef-building” coral species on the high seas, which build up massive layers of calcium carbonate and combine with other organisms to form fully functioning reef ecosystems. Just like an enormous tree creates habitats for thousands of birds and insects, these coral species create habitats for a wide variety of fish and bottom-dwelling creatures. 

Q: Where did you find most of them? 

A: Our study revealed that most of the coral reefs on the high seas grow on structures with steep topographies, including underwater mountains known as seamounts. For example, there are two underwater seamount chains that stretch across 2,900 kilometers (1,800 miles) of the South Pacific, from the coast of Peru to Easter Island in Polynesia. In the high seas area of these mountain chains, several peaks come to within a few hundred feet of the ocean’s surface, where we found several species of reef-building corals. 

One important aspect of our study is that although we were limited by what historic data is available on the high seas — which is minimal — we were still able to identify high seas reefs all over the world. This means that we are just looking at the tip of the iceberg; if we were to target explorations using deep-sea submersibles and other modern technologies, I am certain we would find many more reefs and a wealth of marine biodiversity across the high seas.  

Q: How do coral reefs on the high seas differ from other coral reefs closer to shore?

A: Most of the reef-building coral species we found on the high seas were deepwater species and look very different from what you might find in shallow-water tropical reefs such as the Florida Keys or the Great Barrier Reef. Although not as bright and colorful as the reefs most are familiar with, these deep-sea environments are just as biodiverse and essential to the health of our oceans as surface reefs.

Due to their remoteness, coral reefs on the high seas are largely isolated from many of the human impactsthat near-shore reefs closer to civilization face, including climate change, coastal development, overfishing and pollution. As near-shore coral reefs become increasingly degraded, coral reefs on the high seas will provide critical refuges for marine life that depend on these ecosystems, while helping to “reseed” degraded coral populations closer to shores. Therefore, protecting these coral reefs on the high seas is extremely important because they might be our only lifeline when the reefs on our doorsteps start to disappear. 

Q: If coral reefs on the high seas face fewer threats from near-shore human activities, then what are we protecting them from?

A: Two of the biggest threats to coral reefs on the high seas are deep-sea mining and destructive fishing practices such as deep-sea trawling

Along with an array of unique marine species, precious and rare metals such as manganese, nickel, copper, cobalt and more can be found on the deep-sea floor — and many mining companies are eager to start exploring these areas. The problem: Research shows that deep-sea mining is likely going to have devastating impacts to marine biodiversity. In essence, deep-sea mining requires large machines to scrape the seafloor, killing any fish, coral or small creatures living there in the process. And that is just the most immediate impact — there are more indirect impacts from the sediment plumes, light, toxins and noise generated by deep-sea mining that will negatively affect marine life far beyond actual mining sites. These conditions are bad in any ocean ecosystem, but particularly dire in the deep sea because most of the coral and fish in these environments live over hundreds or thousands of years and are accustomed to stable conditions, similar to the redwood forests of California. If destroyed, it could take thousands to millions of years for these ecosystems to recover — if they can recover at all. 

Q: So how do we protect them? 

A: More time is needed to allow for a better scientific understanding of the risks associated with deep-sea mining. The deep sea covers the biggest portion of the world and hosts up to 10 million species. Several mining companies are already prospecting deep-sea minerals and are ready to start mining if regulations pass. For example, one coral reef in international waters off the coast of Brazil documented by our study is located only 56 kilometers (35 miles) away from an active exploration contract for deep-sea minerals. Before any deep-sea mining takes place, we need to understand where the most vulnerable and special ecosystems are located on the high seas, so we can protect them. If these ecosystems are lost as a result of human activities, they will likely be lost forever.   

Daniel Wagner is an ocean science technical advisor for Conservation International’s Center for Oceans. Kiley Price is a staff writer at Conservation International. Want to read more stories like this? Sign up for email updates here. Donate to Conservation International here.