Scientists Just Discovered a 600-Mile-Long Coral Reef in the Muddy Amazon

April 22, 2016 | Joanne Kennell

Satellite image of the mouth of the Amazon river
Photo credit: NASA

"I was flabbergasted.”

An international team of researchers has discovered something very unexpected: a 1,000-kilometer (600-mile) coral reef hidden under the muddy waters at the mouth of the Amazon river. It is a sponge and coral reef that stretches from the southern tip of French Guiana all the way to the state of Maranhão in Brazil.

Considering just this week, scientists admitted that 75 percent of the Great Barrier Reef has been bleached and that large portions might not recover, this is something the world needed to hear.

To learn there is another reef is fantastic news, but you may be wondering how it went so long without anyone noticing it?

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It has to do with where the reef is located. The mouth of the Amazon is a little bit of a mess because about one-fifth of all the water that flows from Earth’s rivers every day, flows there. Given that amount of water, you are bound to get loads of nutrients, waste, and organic matter, resulting in a lot of mud and the triggering of algae blooms, both of which cloud the water.

"I kind of chuckled when [Brazilian oceanographer Rodrigo Moura] first approached me about looking for reefs. I mean, it’s kind of dark, it’s muddy — it’s the Amazon River," one of the researchers involved, Patricia Yager, told Robinson Meyer of The Atlantic.

"But he pulls out this paper from 1977, saying these researchers had managed to catch a few fish that would indicate reefs are there. He said, 'Let’s see if we can find these,'" she continued.

The paper describes a species of reef fish and sponges unique to the tropical flora and fauna you would find in the islands of the Caribbean, being dredged up from the mouth of the Amazon. However, at the time, no one really gave it much thought.

In fact, Yager wasn’t there to look for the reefs. She was using the RV Atlantis to look into how the Amazonian plume — where a stream empties into a lake — was affecting carbon dioxide absorption in the ocean. However, to get approval to study the mouth of the Amazon, she needed Brazilian oceanographers, one of which was Rodrigo Moura, who asked for her help to look for the reef.

To everyone’s surprise, the dredger came up with sponges, stars, and fish. "I was flabbergasted, as were the rest of the 30 oceanographers," Yager told The Atlantic.

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This reef is now the northernmost known in Brazil. What’s perplexing researchers is how the reef can even exist there at all, given that all the mud in the Amazonian plume keeps it sheltered from the sun most of the time. However, some have suggested that the biology of the reef changes depending on its location and how much sun it gets.

There is still a lot to learn about the reef, and according to Rebecca Albright, an oceanographer and coral researcher from the Carnegie Institute for Science who wasn't involved in this study, the discovery is a really big deal.

"Traditionally, our understanding of reefs has focused on tropical shallow coral reefs which harbour biodiversity that rivals tropical rainforests," she said to The Atlantic. "The new Amazonian reef system described in this paper is another example of a marginal reef that we didn't previously know existed."

The findings will soon be published in the journal Science.

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