- Brazilian state oil and gas company Petrobras has started drilling in the Equatorial Margin after years of political, scientific and environmental disputes over the risks posed by oil exploration at the mouth of the Amazon River.
- Researchers warn that the Amazon Reef system harbors a wealth of biodiversity and has not been widely studied, despite being close to Petrobras’s exploration block.
- Scientists disagree about the composition and extent of the Amazonian reefs, while environmentalists denounce attempts to downplay their ecological importance.
- Experts warn that an oil spill could reach mangroves, small-scale fisheries, and even neighboring countries, due to strong marine currents in the area.
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.”
The controversy over Amazon corals
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.
However, two years earlier, in 2022, a group of 21 Brazilian scientists had published a study titled “The Great Amazon Reef System: A fact.” They listed evidence and scientific works that confirmed the existence of the reef system, and refuted inconsistencies in other publications.
“When Petrobras took over the block, there was a lot of political activity,” says study lead author Thomás Banha, an oceanographer at the University of São Paulo. “In parallel, some papers claimed that the reef didn’t have much wildlife diversity, trying to mischaracterize that ecosystem. In some of those works, the authors even stated that there was no conflict of interest, but then they thanked ‘such‑and‑such oil company’ at the end of the articles for funding the studies.”
Little is known about the Blue Amazon
In their study, Banha and colleagues acknowledged little was known about the reef system. “Less than 5% of [this ecosystem] has been studied in detail and further research is evidently necessary. Basic data, such as detailed information on bathymetry and current patterns and the relative abundance of fish and benthic organisms, are still lacking,” they wrote.
Many scientists agree that knowledge about wildlife biodiversity in the Amazon basin is limited.
“There is still a huge lack of knowledge. In the Amazon, everything is far away and extremely large,” says Bianca Bentes, a professor of aquatic ecology and fisheries at the Federal University of Pará. “That area is hard to access, with very strong currents, and navigation is difficult. It takes several days just to reach the edge of the continental shelf, depending on current speed and rainfall. And all this requires a lot of financial resources.”
Paes, the oceanography professor, says that, in the past, research in the biome was mainly focused on the forest — the “green” Amazon. “The vigor of the biome has restricted investments in marine science. Without a vessel, for example, marine geological studies can’t be done.”
However, money is gradually appearing for new studies. Paes will go on another expedition in late 2026, and Bentes just started a 48-month project to survey and characterize not only the environment but also what is fished there.
Many of the studies currently approved are funded by Petrobras itself, despite the potential conflict of interest highlighted by Banha.
“New studies should clarify the issue of coral reefs in the region,” Figueiredo Jr. says. “There used to be few studies in the Amazon Mouth basin, but several initiatives by the Navy, the Brazilian Geological Survey and Petrobras — which plans to invest up to 17 billion reais [$3.3 billion] between 2026 and 2029 — now involve researchers and universities, especially in the Equatorial Margin.”
Rodrigo Agostinho, who headed IBAMA, the federal environmental agency, until April 2025, says there are few research centers and universities in the Amazon, and that existing studies were produced by institutions from other parts of the country. “Indeed, data on the region are scarce. What we have is information gaps. It’s different, for example, from the coasts of Rio de Janeiro, Espírito Santo and São Paulo [states], where most of the country’s oil production is concentrated.”
Impacts of a potential oil spill
What environmentalists and scientists say they fear the most about oil exploration in the Equatorial Margin is a potential spill and its impact not only on Brazil but also on neighboring countries. Petrobras notes that Block 59 is located more than 160 km (100 mi) from the nearest coastline, and more than 500 km (300 mi) from the mouth of the Amazon River, and that, in the event of an accident, the oil would float.
However, researchers point to several particularities of the region. According to Martinelli Filho, Brazil’s northern coast is higher than other regions, making it more susceptible to macrotidal variations such as those that occur on the Pará coast, where water levels can rise by more than 5 m (16 ft) during the day. This range can be even larger at some points along the Amapá coast. “If a spill occurs near the coast, under a macrotidal regime, these residues can be pushed into the coastal zone.”
Another major concern is the strength of marine currents. In 2024, Greenpeace Brasil conducted a second expedition to the region, where it performed an experiment using seven GPS‑equipped buoys released at different points of the reef system to understand the movements of surface currents.
“Our goal was to find out where the oil would go during a potential spill and at what speed,” says Greenpeace’s Andrade. “Two buoys reached the Brazilian coast within 24 hours, on the coast of Amapá and on Marajó Island. The other five quickly reached international waters — in 16 hours, one of them had already crossed the border into French Guiana. Another buoy arrived in Suriname, and one even made it to Florida.”
Beyond environmental consequences, specialists warn about the implications of an accident for local communities. On the Amazonian coast, small-scale fishing still prevails over industrial fishing. One of the most important species is snapper (Lutjanus purpureus), Brazil’s second most valuable marine fish export.
“Fishing and fishers are more important here than in the south, southeast and northeast of the country,” Martinelli Filho says. “A spill would have not only economic but also social impacts, and much stronger than in other regions of Brazil.”
Martinelli Filho, who is an expert in environmental impact studies, says the reality of Brazil’s Amazonian states is one of the most critical points to consider. He says today’s human resources and infrastructure would still be insufficient to respond to a major accident. “Oil exploration may become viable in the future, but not now,” he says. “In the Campos Basin, on the coasts of São Paulo or Rio de Janeiro, a logistics and risk‑management system has been in place for decades, but it is still incipient on the Amazonian coast.”
Former IBAMA president Agostinho says this lack of structure was decisive for the agency to deny several license requests. He says the procedure was extremely rigorous and underscores that, precisely because of that, it took more than 10 years.
“Despite all opinions to the contrary, the license was only granted after Petrobras actually built the structure in the Oiapoque area to respond to a potential accident,” he says. “For a decade, the company insisted that, if there was any problem, its base in Belém, 700 kilometers [430 mi] from Block 59, would handle the accident. IBAMA considered it completely unfeasible.”
Legal action
In October 2025, shortly after IBAMA gave the green light for Petrobras to begin prospecting in the Equatorial Margin, eight organizations representing Indigenous peoples, Afro-Brazilian quilombola communities, and fishers filed a lawsuit at the Federal Court of Pará, with the Public Prosecution Service (MPF) as a co‑plaintiff. They sought the exploration license for Block FZA‑M‑59 to be nullified or suspended, alleging that communities were not consulted, the project’s climate impacts were ignored, and the licensing procedure had serious modeling flaws, putting biodiversity at risk.
In a statement sent to Mongabay, Petrobras said “the exploratory project on the Equatorial Margin includes drilling an offshore well more than 200 km [120 mi] from Indigenous lands. In this exploratory phase, no infrastructure will be built near Indigenous lands.” It also said it has “implemented a broad communication process to share transparent information and to strengthen dialogue with civil society and Indigenous communities in the Amazon Mouth’s sedimentary basin.”
The lawsuit filed by NGOs and prosecutors has yet to be resolved. However, by order of the First Federal Regional Court (TRF1), the case that would have been heard in Pará was transferred to Amapá — the state of Senate President Davi Alcolumbre, an ardent supporter of oil exploration in the Equatorial Margin.
Brazil’s new energy frontier
In the past, Petrobras had already tried looking for oil in this same region, but in coastal areas. It found nothing. “More than a hundred drillings were made in areas that were even more sensitive than it is today, but perhaps not with the current complexity — very deep drillings far from the coast and with very strong marine currents as well,” Agostinho says.
Adding to the concerns of those opposed to oil exploration in the Amazon, less than two months after drilling started for the Morpho well in early January, Petrobras had to halt operations after almost 15,000 liters (4,000 gallons) of fluid leaked from a drilling ship. The incident prompted a 2.5 million reais ($385,000) fine from IBAMA, and an order from the National Agency of Petroleum, Natural Gas and Biofuels (ANP) for a series of new contingency measures.
According to IBAMA’s technical report, the fluid posed “medium-level risk to both human health and the aquatic ecosystem.” But Petrobras challenged this characterization. “The company reiterates that the fluid is biodegradable, non‑persistent, non‑bioaccumulative and non‑toxic, according to the product’s Safety Data Sheet. It meets all of the environmental agency’s standards and does not cause any damage to the environment,” the company said in a statement.
Petrobras did not respond when asked whether it would appeal the fine. After years trying to obtain a license, it seems unlikely the company will fight over 2.5 million reais fine. The company’s Strategic Plan includes investing $3.1 billion in the Equatorial Margin up to 2028, drilling 16 wells. That’s 41.5% of what Petrobras plans to invest in oil exploration elsewhere in Brazil and abroad over the next three years.
Suely Araújo, another former IBAMA president, is the public policy coordinator at the Climate Observatory, one of the organizations that filed the lawsuit in Pará. She criticizes Brazil’s expansion of oil exploration into new frontiers, especially those that are “ecologically very fragile.”
“Most of Brazil’s oil comes from the pre‑salt reserves, and we export more than half of it. So the demand is not domestic or energy-related; it’s for export. It’s focused on having oil to make money,” she says.
The Brazilian government says revenue generated from such exports goes toward funding the country’s energy transition to renewable sources. “That claim only makes sense in already opened oil‑producing areas. Expanding production to fund the transition is not logical,” Araújo says.
Petrobras estimates the initial drilling stage will take five months, but with the fluid leak, the completion date has been pushed back to an unknown date. If high-quality oil is found, the company will probably apply for a license to prospect in additional sites to try to understand the extent of the production area. It attempted to include three additional sites together with Block 59, but was denied by IBAMA.
Agostinho says that if oil is found, a new licensing process will be launched, taking into account, among other things, new studies that may be published. “Everything changes. First, because production requires large structures that do not exist in the region. Drilling is being done with a drill ship. There is no oil platform there yet. And exploratory licensing is a single‑phase process, while production licensing is three‑phased, including several other types of permits,” Agostinho says. “Petrobras is used to this process, but everything will start from scratch again.”
Banner image: Sponge garden in the Amazon Reef system. Image courtesy of INCT Biodiversity of the Blue Amazon.
This story was first published here in Portuguese on May 18, 2026.
Citations:
Moura, R. L., Amado-Filho, G. M., Moraes, F. C., Brasileiro, P. S., Salomon, P. S., Mahiques, M. M., … Thompson, F. L. (2016). An extensive reef system at the Amazon River mouth. Science advances, 2(4), e1501252. doi:10.1126/sciadv.1501252
Loreau, M., Mouquet, N., & Holt, R. D. (2003). Meta‐ecosystems: A theoretical framework for a spatial ecosystem ecology. Ecology Letters, 6(8), 673-679. doi:10.1046/j.1461-0248.2003.00483.x
Santos Filho, J. R., Anjos, J. V., Silva, C. G., Barros Filho, A. K., Dias, G. T., Figueiredo, A. G., … Carneiro, J. C. (2025). Mesophotic encrusting biotas and bioclastic deposits on the Western South Atlantic Equatorial margin: Geomorphological insights from the Amazon and Semi-Arid Coast Systems. Marine Geology, 484, 107544. doi:10.1016/j.margeo.2025.107544
Banha, T. N., Luiz, O. J., Asp, N. E., Pinheiro, H. T., Magris, R. A., Cordeiro, R. T., … Francini-Filho, R. B. (2022). The Great Amazon reef system: a fact. Frontiers in Marine Science, 9, 1088956. doi:10.3389/fmars.2022.1088956
Francini-Filho, R. B., Asp, N. E., Siegle, E., Hocevar, J., Lowyck, K., D’Avila, N., … Thompson, F. L. (2018). Perspectives on the Great Amazon Reef: Extension, biodiversity, and threats. Frontiers in Marine Science, 5. doi:10.3389/fmars.2018.00142
Cite this article
Suzana Camargo (2026). As Amazon oil drilling begins, scientists warn of risks to a little-known reef. Mongabay Conservation news. DOI: https://doi.org/10.66709/news-321998Credits
