A Brazilian volunteer cleans oil at a beach in Lauro de Freitas in Bahia state on 2 November. Small blobs have now reached Abrolhos Bank, home to some of Brazil’s most iconic marine species.

ANTONELLO VENERI/AFP via Getty Images

Mysterious oil spill threatens marine biodiversity haven in Brazil

Marine scientists in Brazil are closely monitoring the incursion of a mysterious oil spill into the largest biodiversity hot spot in the South Atlantic Ocean. The region, known as the Abrolhos Bank, shelters almost 9000 square kilometers of reefs in shallow, warm waters along the central part of the Brazilian coastline.

More than 4000 tons of crude oil residue from an unknown source have landed on the country’s northeast seaboard since late August, contaminating hundreds of beaches, estuaries, reefs, and mangroves along a 2500-kilometer stretch of shoreline.

Concerns escalated earlier last week as the wave of sticky oil patches began to encroach on the Abrolhos Bank’s northern border, on the southern coast of Bahia state. By Saturday morning, the first small blobs of petroleum had landed on the rocky shores of the Abrolhos Marine National Park archipelago, 60 kilometers offshore—home to some of Brazil’s most iconic marine species, such as the endemic Brazilian brain coral (Mussismilia braziliensis) and the endangered blue parrotfish (Scarus trispinosus).

A fleet of navy ships has been patrolling the region since Wednesday, looking to spot and intercept any large incoming oil patches. But there is nothing it can do for smaller blobs, which have to be cleaned up by hand.

“The oil is coming. How much of it will land here and what ecosystems will be impacted remains to be seen; but it could be tragic,” says Rodrigo Leão Moura, a marine scientist at the Federal University of Rio de Janeiro (UFRJ) in Rio de Janeiro, Brazil, who is monitoring the crisis.

Chemical analysis indicated early on that the oil was from Venezuela, but the source of the spill was a complete mystery for the first 2 months. President Jair Bolsonaro’s government was heavily criticized for not responding quickly or strongly enough to the wave of contamination. Although it eventually deployed ships and troops to help with the cleanup, the administration also tried to blame nongovernmental organizations and left-wing conspirators for the crisis, as it did for massive fires and a rising deforestation rate in the Amazon. Minister of the Environment Ricardo Salles even tweeted a picture of a Greenpeace ship on 24 October, suggesting—without any proof—that it was responsible for the spill.

The oil is coming. … It could be tragic.

Rodrigo Leão Moura, Federal University of Rio de Janeiro

On Friday, the Brazilian Federal Police finally released the name of a real suspect: the Bouboulina, a Greek tanker that passed the Brazilian northeast coast in late July, carrying 1 million barrels worth of crude oil from Venezuela to Malaysia. According to the investigation, satellite images show a big oil stain appearing offshore on 29 July, about 730 kilometers off the coast of Paraíba state, just as the Bouboulina passed by. The company responsible for the ship denies responsibility and says the Bouboulina delivered all of its cargo to Malaysia.

But the suspicion fits well with computer simulations run by UFRJ’s engineering institute (Coppe), which indicate that the oil came from an offshore source about 700 kilometers away and was spilled about 1 month before it hit land. “The distribution pattern of the oil along the coast and the possible source indicated by the police are both consistent with our model,” Coppe oceanographer Luiz Assad told Science.

Federal investigators estimated that the Bouboulina spilled—either accidentally or intentionally—about 2.5 thousand tons of crude oil, but it’s unknown how accurate that estimate is or how much of the spilled oil will reach land. Any amount of oil that reaches Abrolhos is reason for concern, however, says Ronaldo Francini Filho, a marine biologist at the Federal University of Paraíba in João Pessoa, whose team plans to inspect the reefs with a remotely operated vehicle this week. “It’s an extremely sensitive environment, already suffering the effects of climate change and other anthropogenic impacts,” Francini Filho says.

In addition to its many coral reef habitats, Abrolhos is an important sanctuary for seabirds and humpback whales and an important destination for marine ecotourism. Its 880-square-kilometer marine national park, founded in 1983, is Brazil’s oldest.