Unique coral reef system discovered at the mouth of the Amazon

With tales of widespread bleaching and the ill effects of climate change dominating headlines, there’s finally some good news involving coral reefs : researchers have discovered an entirely new, previously undetected reef system at the mouth of the Amazon River.

The unexpected find, which is detailed in the April 22 edition of the journal Science Advances, was rather unexpected because larger rivers that flow into the oceans in areas known as plumes often have gaps in the reef distribution along their tropical shelves, the authors explained.

However, a team of scientists from the University of Georgia and the Federal University of Rio de Janeiro found a broad reef ecosystem hidden beneath a plume of river water, which according to Discovery News is what kept it hidden for so long. They discovered the reef through a process known as multibeam acoustic sampling, and collected samples to confirm their find.

“There were some studies back in the 1950s that suggested the presence of reefs,” senior author Fabiano Thompson, an oceanographer and professor of marine biology at the Federal University of Rio de Janeiro, told the site, “but none pinpointed the reef bodies, dimensions, locations, and compositions.”

System unlike any previous discovered, but may already be threatened

Thompson and his colleagues traveled to the Amazon to study river plumes, looking for evidence of a reef system along the continental shelf in the area. What they found was an extensive system that was hope to a wide variety of different marine life, including sponges, several different types of algae, corals, jellyfish-like predators known as hydroids, and dozens of fish species.

“Our expedition… was primarily focused on sampling the mouth of the Amazon,” Patricia Yager, an associate professor of marine sciences at the University of Georgia, noted in a statement. “We brought up the most amazing and colorful animals I had ever seen on an expedition.” Additional analysis led to the discovery of a reef ecosystem unlike any scientists had ever seen before.

As Discovery News explained, the new reef system receives extremely little to no light at various points along the shelf, creating conditions similar to those of so-called shadow zones – areas that are located up to thousands of feet beneath the surface of the water and which are marked by low levels of oxygen. Furthermore, while most reefs develop in waters that are transparent and which have little nutrient content, this system was found in murky, sediment-rich waters.

“The paper is not just about the reef itself, but about how the reef community changes as you travel north along the shelf break,” said Yager. “In the far south, it gets more light exposure, so many of the animals are more typical reef corals and things that photosynthesize for food. But as you move north, many of those become less abundant, and the reef transitions to sponges and other reef builders that are likely growing on the food that the river plume delivers.”

The two systems are “intricately linked,” she added, but the research team is concerned that the newfound reefs are already in danger. “From ocean acidification and ocean warming to plans for offshore oil exploration right on top of these new discoveries,” Yager said, “the whole system is at risk from human impacts.”

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Image credit: NASA

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