The Amazon region always invites superlatives: the world’s largest tropical forest, the planet’s largest continuous mangrove belt, the river with the largest water volume and length on Earth. That makes any kind of exploratory activity in the region — and its potential impacts on this unique ecosystem — cause for great concern.
That’s the case with exploration activities currently being carried out by Brazilian state‑owned oil and gas company Petrobras in the area known as the Equatorial Margin. This area includes the coastal and offshore strip starting at the mouth of the Amazon river and fanning out into the Atlantic, off the Brazilian states of Amapá and Rio Grande do Norte.
The environmental license for Petrobras to start prospecting for oil and gas was granted by Brazil’s federal environmental agency, IBAMA, in October 2025, after several denied requests, strong political pressure — including from President Luis Inácio Lula da Silva himself — and strong criticism from environmentalists and civil society organizations.
One of the key concerns raised by experts about Petrobras’s operation centers on the Amazon Reef system, located less than 40 kilometers (25 miles) from block FZA‑M‑59, where Petrobras is drilling its Morpho well.
Known since the 1970s, the Amazon Reef system was only officially described by a group of Brazilian researchers in 2016. The following year, a Greenpeace research vessel equipped with a small submarine released the rare images of that environment, which covers an estimated 9,500 square kilometers (about 3,700 square miles) and serves as a biodiversity corridor between the Atlantic Ocean and the Caribbean Sea.
One of the surprises was the occurrence of corals, since water turbidity and lack of light usually don’t make for ideal conditions for these organisms to proliferate.
“The reef environment in the Equatorial Margin hosts an enormous variety of organisms, with vast fields of rhodoliths, starfish, calcareous algae, corals, and huge gardens of century‑old sponges,” says Eduardo Tavares Paes, a professor of oceanography at the Federal Rural University of Amazonia.
In November last year, Paes spent 15 days in the region, leading an unprecedented biodiversity mapping study for the Biodiversity of the Blue Amazon, a project under Brazil’s National Institute of Science and Technology (INCT).
This reef system is marked by its interdependence with other ecosystems at the mouth of the Amazon River. “The river’s freshwater plume directly influences the reef environment. It carries a large amount of organic material and nutrients that serve as food for marine life,” Paes says. “It’s a series of interconnected ecosystems known as a meta‑ecosystem. Many species that are born in mangroves, for example, will later live on the reef.”
Scientists are quick to point out that this is nothing like the Great Barrier Reef off Australia. And corals are only one type of organism found in the Amazon Reef system, considered by experts to be quite complex and unusual.
José Eduardo Martinelli Filho, a professor at the Federal University of Pará, says that while reefs typically conjure up images of corals, they can also be composed of different organisms. “The seafloor is usually sand, mud or clay. But when there is some type of consolidated substrate such as rocks or limestone, formed or colonized by living organisms, that’s what we call a reef,” he says.
“Therefore, not every reef is made of coral. The Amazonian reef has corals, but sponges or red algae prevail and form rhodoliths. It’s a very important and relevant system that can sustain a large part of the region’s fishing.”
Since 2017, however, after Greenpeace released the images and launched the international campaign “Defend Amazon Corals” to stop oil exploration at the mouth of the Amazon River, criticism began to appear within the academic community itself, from scientists who challenged the existence of corals and even the value of this ecosystem as a whole.
“In recent years, since 2018, 2019, we have seen a strong debate, even encouraged by Petrobras itself, to delegitimize the ecological importance of the Amazon Reef system, for example, by claiming that it was not alive or that there were no corals,” says Mariana Andrade, and oceanographer and coordinator of Greenpeace Brasil’s ocean campaigns.
Alberto Figueiredo Jr., a retired geology professor from Fluminense Federal University, authored a 2018 paper on the “myths and truths” of the Amazon Reef’s corals. He says the “false preservation campaign” is being pushed by “laypeople” lacking scientific knowledge about the presence of living coral reefs close to the oil exploration site.
“Live corals and calcareous algae are not observed in the areas where the exploratory blocks are located in the Amazon Mouth basin. On the platform’s edge, at depths between 80 and 150 meters [260-500 feet], there are positive reliefs of consolidated sandstones capped by a carbonate crust. This feature has been termed mesophotic reefs in the literature,” Figueiredo Jr. told Mongabay.
“From the coast of Amapá up to the river mouth,” he added, “these mesophotic reefs are covered by mud and virtually no live corals or calcareous algae are observed. Of course there might be some individual live corals or calcareous algae, but I disagree that they are reef‑forming living corals.”
But Martinelli Filho disputes this. “What [Figueiredo Jr.] calls dead corals are probably rhodoliths, structures with a calcium carbonate core, but their outer surface is alive and composed of red algae that photosynthesize. That’s a highly important substrate that animals compete to colonize, and several fish and invertebrates feed on it,” he says. “And this is not an opinion; it’s not an indication. It’s a fact.”
In addition to some scientists, Petrobras executives themselves also doubted what was thought to exist in the Amazon Reef system. In 2024, during an open lecture at the Federal University of Rio de Janeiro (UFRJ), the company’s chief exploration and production officer, Sylvia Anjos, said there were no corals in the Amazon River’s Mouth.
“That’s not true; that’s scientific ‘fake news,’” she said at the time. “There are carbonate rocks similar to corals, but they are not corals. They are old rocks.” She added that studies conducted by the company’s research center in partnership with more than 10 institutions had found no corals.
