The first pictures of a huge coral reef system discovered in the Amazon last year have been released by environmental campaigners.
The Amazon Reef is a 9,500 sq km (3,600 sq miles) system of corals, sponges and rhodoliths, Greenpeace says.
The reef is almost 1,000 km (620 miles) long, and is located where the Amazon River meets the Atlantic Ocean.
Oil drilling could start in the area if companies obtain permits from the Brazilian government, the group warns.
"This reef system is important for many reasons, including the fact that it has unique characteristics regarding use and availability of light, and physicochemical water conditions," researcher Nils Asp, from the Federal University of Para, said in a statement.
"It has a huge potential for new species, and it is also important for the economic well-being of fishing communities along the Amazonian coastal zone."
Scientists were surprised by the discovery, in April 2016, as they thought it was unlikely that reefs would be found it the area given unfavourable conditions," they said in a paper in the scientific journal Science Advances.
The reef ranges from about 25-120m deep (82-393ft)
Mr Asp now says that his team wants to gradually map the system. At the moment, only 5% of it has been mapped.
"Our team wants to have a better understanding of how this ecosystem works, including important questions like its photosynthesis mechanisms with very limited light."
But Greenpeace says drilling in the area means a "constant risk of an oil spill".
Campaigner Thiago Almeida said environmental licensing processes for oil exploration there are already under way.
"The Cape Orange National Park, the northernmost point of the Brazilian state of Amapa, is home to the world's largest continuous mangrove ecosystem and there is no technology capable of cleaning up oil in a place of its characteristics," the group said.
"In addition, the risks in this area are increased due to the strong currents and sediment that the Amazon River carries."
The group said that, so far, 95 wells have been drilled in the region, and 27 of them were abandoned as a result of mechanical incidents - the rest due to the absence of economically or technically viable gas and oil.