Researchers from the University of Georgia (UGA) and the Federal University of Rio de Janeiro have discovered a new reef system at the mouth of the Amazon River. The discovery of a reef in the Amazon plume is unexpected, as large rivers typically create gaps in reef distribution along the tropical shelves as they funnel into the world's ocean plumes.
The Amazon plume is an area where freshwater from the river combines with the salty Atlantic Ocean and has a large influence on the salinity, pH, light penetration and sedimentation of the tropical North Atlantic Ocean. These conditions typically create 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 Patricia Yager, professor at UGA and principal investigator of the study. "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."
Using multibeam acoustic sampling of the ocean bottom, the team pinpointed the location of the reef system and then collected samples to confirm their findings.
"We brought up the most amazing and colorful animals I had ever seen on an expedition," Yager said.
After confirmation, a full team of researchers returned to the site in 2014 and was able to fully document the system, which will help scientists gain a better perspective of the reef community and its unique characteristics. In addition, they could reveal the nature of the microorganisms thriving below the river plume.
"The 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," 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," she added. "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."
The data will also be helpful in understanding the human-induced effects of climate change on the Amazon River's newly discovered reef system.
"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.
The findings were published in the April 22 issue of the journal Science Advances.
