Massive 600 mile long coral reef found at the mouth of the Amazon: Scientists stunned by discovery – but say it is already under threat from oil exploration
3,600 sq mile (9,300 sq km) coral reef system was below muddy waters
600-mile long reef ranges from about 30-120m deep
Stretches from French Guiana to Brazil’s Maranhão state
A massive new reef system has been found at the mouth of the Amazon River, the largest river by discharge of water in the world.
Researchers were stunned to find the huge 3,600 sq mile (9,300 sq km) coral reef system below the muddy waters.
The 600-mile long reef, which ranges from about 30-120m deep and stretches from French Guiana to Brazil’s Maranhão state.
Researchers say the find was not suspected because many of the world’s great rivers produce major gaps in reef systems, where no corals grow.
The Amazon plume, an area where freshwater from the river mixes with the salty Atlantic Ocean, 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.
The researchers say the reef appears to be thriving below the freshwater ‘plume’, or outflow, of the Amazon.
Compared to many other reefs, the scientists say in a paper in Science Advances on Friday, it is is relatively ‘impoverished’.
Despite this, they found over 60 species of sponges, 73 species of fish, spiny lobsters, stars and much other reef life.
‘We brought up the most amazing and colorful animals I had ever seen on an expedition,’ said Patricia Yager, an associate professor of marine sciences in UGA’s Franklin College of Arts and Sciences and principal investigator of the River-Ocean Continuum of the Amazon project.
Researchers were stunned to find the huge 3,600 sq mile (9,300 sq km) coral reef system below the muddy waters
‘Our expedition into the Brazil Exclusive Economic Zone was primarily focused on sampling the mouth of the Amazon,’ said’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 difficulty of finding the old map coordinates with modern GPS notwithstanding, the team used multibeam acoustic sampling of the ocean bottom to find the reef and then dredged up samples to confirm the discovery.
The Brazilian researchers then organized a full team and took a Brazilian Navy research vessel back to the site in 2014, when they were able to collect and fully describe the findings for the study.
However, the reef is already in danger.
According to the paper, the Brazilian government has sold 80 blocks for oil exploration and drilling at the mouth of the Amazon and 20 of these are already producing oil – some, it is thought, right on top of the reef.
‘These [exploration] blocks will soon be producing oil in close proximity to the reefs, but the environmental baseline compiled by the companies and the Brazilian government is … largely based on sparse museum specimens.
‘Such large-scale industrial activities present a major environmental challenge,’ said the study’s authors.
Microorganisms thriving in the dark waters beneath the river plume may provide the connection between the river and the reef.
‘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,’ said Yager.
‘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, who spent two months in Brazil as a Science Without Borders visiting professor.
‘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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