A new reef system has been found at the mouth of the Amazon River by an international group of researchers from Brazil and the United States.
The Amazon River meets the Atlantic Ocean and creates a plume where freshwater and salt water mix. Image credit: Lance Willis.
The team, led by Dr. Rodrigo Moura from the Federal University of Rio de Janeiro, reported their discovery on April 22 in the journal Science Advances.
“As large rivers empty into the world’s oceans in areas known as plumes, they typically create gaps in the reef distribution along the tropical shelves — something that makes finding a reef in the Amazon plume an unexpected discovery,” the scientists explained.
The Amazon River plume is an area where freshwater from the river mixes with the salty Atlantic Ocean. It affects a broad area of the tropical North Atlantic Ocean in terms of salinity, pH, light penetration and sedimentation, conditions that usually correlate to a major gap in Western Atlantic reefs.
“Our expedition into the Brazil Exclusive Economic Zone was primarily focused on sampling the mouth of the Amazon,” said co-author Dr. Patricia Yager from the University of Georgia.
“But Dr. Moura had an article from the 1970s that mentioned catching reef fish along the continental shelf and said he wanted to try to locate these reefs.”
The scientists used multibeam acoustic sampling of the ocean bottom to find the reef and then dredged up samples to confirm the discovery.
“We brought up the most amazing and colorful animals I had ever seen on an expedition,” Dr. Yager said.
The Amazon plume and its effects on the global carbon budget converged with the discovery of the reef system to provide scientists a wider view of the reef community, its variation and changes.
Microorganisms thriving in the dark waters beneath the river plume may provide the trophic connection between the river and the reef.
“Our paper is not just about the reef itself, but about how the reef community changes as you travel north along the shelf break, in response to how much light it gets seasonally by the movement of the plume,” Dr. Yager said.
“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. So the two systems are intricately linked.”
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Rodrigo L. Moura et al. 2016. An extensive reef system at the Amazon River mouth. Science Advances, vol. 2, no. 4, e1501252; doi: 10.1126/sciadv.1501252
