"Threats to the reef system, which lies 70–220 metres below the ocean surface, are of great concern to some scientists. It has been difficult to explore the area because of turbulent waters, but studies estimate that the reef spans between 9,500 and 56,000 square kilometres across the mouth of the Amazon12. When it was first described by scientists in the 1970s, researchers did not observe rich biodiversity. But studies in 20162 and 20193 found a thriving ecosystem that’s home to corals, sponges and fish communities.
“It is huge, and it is sensitive,” says Ronaldo Francini-Filho, a marine ecosystems researcher at the University of São Paulo in Brazil. “And we don’t know even 5% of what’s down there.” Nature, 12 July 2023.