The Amazon River is teeming with exotic and unusual wildlife. However, scientists didn’t think coral could thrive near its muddy waters. Now, a new study published in the journal Science reveals that the mouth of the world’s second-longest river is home to a massive coral reef ecosystem, the Los Angeles Times reports.

The coral formation is 600 miles long and covers more than 3600 square miles of ocean floor from French Guiana to Brazil’s Maranhão State. Researchers think the underwater structure could reveal new ecological discoveries, and teach them more about how coral reefs can survive in sub-optimal conditions.

“This is something totally new and different from what is present in any other part of the globe,” Fabiano Thompson, an oceanographer at the Universidade Federal do Rio de Janeiro in Brazil, told Smithsonian. “But until now, it’s been almost completely overlooked.”  

According to The Atlantic, a team of researchers from the University of Georgia and the Federal University of Rio de Janeiro discovered the coral reef in 2012. The find was serendipitous. Patricia Yager, a professor of oceanography and climate change at the University of Georgia, had planned to study how the murky plume of fresh water that pours from the Amazon into the Atlantic impacts the ocean’s absorption of carbon dioxide. However, Rodrigo Moura, a Brazilian scientist accompanying Yager on her expedition, had other plans. He'd read a paper from 1977 stating that fish caught in the region indicated the presence of a coral reef. Wanting to investigate further, Moura convinced a skeptical Yager to bring a dredge along on their expedition aboard the research vessel Atlantis.

On the expedition, Moura monitored the boat’s seabed sonar. He eventually located a promising spot, and he lowered the dredge. Much to the researchers’ surprise, it came up filled with corals, sponges, stars, and fish. In 2014, the Brazilian scientists returned to the spot, mapped the reefs, and collected more samples.

Scientists originally thought that the Amazon’s muddy plume would prevent reefs from receiving light and oxygen. However, subsequent research revealed that the river’s plume only covers the reef’s southern section three months out of the year, and its north section more than half of the year. As a result, the southern reef is filled with critters, whereas the north is home to many sponges.

On whole, the expedition revealed countless species of algae, soft and stony corals, and fish species. Researchers also found 29 unidentified specimens that might be brand-new species, along with microbes that seem to survive not on light, but on ammonia, nitrogen, and sulfur.

Researchers still have more to learn about this new, unique ecosystem. It might also teach researchers how coral can survive in harsh conditions, as reefs are threatened by coral bleaching worldwide. However, scientists warn that the reef is already threatened by human activity.

"From ocean acidification and ocean warming to plans for offshore oil exploration right on top of these new discoveries, the whole system is at risk from human impacts," Yager said in a news release.

[h/t Los Angeles Times]