Sponges, algae and fish collected from the sea floor by Rodrigo Moura's team are evidence that there is a huge reef at the mouth of the Amazon. According to textbooks, it shouldn't be there PHOTO: FERNANDO MORAES_JBRJ
The reef that nobody saw
An unexpected ecosystem lies below the murky waters at the mouth of the Amazon
Bernardo Esteves | Edição 123, Dezembro 2016
Translated by Flora Thomson-Deveaux
The vast swath of brown water that the Amazon pours out into the Atlantic Ocean is visible from space. The plume, as scientists refer to the mass of freshwater carried along by the river, may occupy an area larger than Peru. The muddy look of the water comes from the volume of sticks, stones, animal and plant remains, detritus, and sediments of all sorts it has picked up over its nearly 7,000-km journey. The Amazon emerges from the Peruvian Andes at an altitude of over 5,000 meters and cuts across the continent, coursing into the ocean near Marajó Island and forming the border between the Brazilian states of Amapá and Pará. Depending on how one measures such things, it may be the longest river on the planet. Some reserve that distinction for the Nile, but there is one point of consensus: the Amazon is clearly the largest river by discharge in the world. In a single given second it may dump enough volume into the sea to fill 120 Olympic swimming pools.
In May of 1975, a United States marine vessel, the Oregon II, skirted Brazil’s northern coast on a scientific expedition to assess shrimp stocks in those waters. Around the mouth of the Amazon, the nets put out by the crew came back full of fish that shouldn’t have been there – species typical of places with ocean reefs. They also turned up a profusion of sponges, rudimentary animals that feed off of organic material filtered out of water. There were so many of them that the researchers referred to the region as having a “sponge bottom.”
These were the life forms generally found on reefs, but marine biology textbooks will tell you that there are no reefs in the estuaries of large tropical rivers like the Amazon. The reason is quite logical: sunlight, scientists assumed, would be unable to penetrate the thick layer of sediment and organic matter swept along by the river. The algae and corals that build reefs – complex calcareous structures on the sea floor that attract fishes and animals from a number of other groups – couldn’t survive without light. The closest coral reefs to the Amazon estuary were to be found at Parcel de Manuel Luís, hundreds of kilometers away. The Parcel de Manuel Luís formation – the largest in South America – is a trap now well known to navigators, having caused the wrecks of some 200 vessels.
The discovery of a sponge bottom in the vicinity of the mouth of the Amazon was announced at a conference in 1977. The pair of researchers who authored the paper, from the Smithsonian National Museum of Natural History, didn’t try to explain the presence of such improbable specimens in the region. But marine biologist Rodrigo Leão de Moura was haunted by the question. “How is it that nobody went back to look into it in all this time, since the ‘70s?” he asked, wide-eyed, on a recent afternoon. Nor was this the only intriguing observation. Fishing hauls in Amapá showed significant quantities of lobsters and a kind of fish known as porgies or seabream, which are commonly found on reefs. “Lobsters don’t live on muddy bottoms, only in places with structural complexity,” Moura pointed out indignantly. There had to be something down there.
Moura is a 43-year-old coral expert who has a goatee and two piercings in his right ear. His workplace at the Federal University of Rio de Janeiro (UFRJ), where he’s been teaching for the past five years, is furnished with all of glassware one might expect to find in a typical biology laboratory, but also boasts diving suits, oxygen canisters, and underwater robots. Moura first saw a chance to put his hypothesis to the test on an afternoon in 2012, when he was introduced to American oceanologist Patricia Yager.
Yager, who is a professor at the University of Georgia, studies how the oceans absorb carbon dioxide – or CO2 – from the atmosphere, and was interested in researching the process in the Amazonian plume. In an interview over Skype, she explained that the plume has a massive effect on the biology of the tropical Atlantic and on the carbon cycle. “It acts like a big CO2 sink,” she said. At the time, Yager was working on a research expedition along the mouth of the river to analyze water samples and understand what was going on. “These were measurements that no one had taken before.”
She had already been to the region in 2010, but her voyage stopped at the border with French Guyana. To navigate in Brazilian waters, she would need the go-ahead from the Brazilian Navy, which only authorizes foreign scientific missions that include Brazilian scientists. Looking to return to the area, she partnered with oceanologist Carlos Eduardo de Rezende, whom she’d met through a colleague. Alongside Fabiano Thompson, Rezende helped her obtain official permission and coordinated the Brazilian side of the project. Rezende himself was set to be the deputy research coordinator on the trip. Family issues intervened, however, and so the job fell into Rodrigo Moura’s lap.
Since there were no coral reefs – Moura’s specialty – in the region, Patricia Yager found herself wondering what sort of research he might conduct on the trip. When she met him as they were preparing the expedition, she’d asked what he would like to study. By way of response, Moura dredged up the 1977 article mentioning the organisms typical of reef life found at the mouth of the Amazon. He showed his American colleague the map with the areas where the specimens had been collected, and said that he wanted to go after the sponge bottom. “Have you been there before?” Yager asked incredulously. “It’s really muddy.” Moura knew it was, but he insisted. “I think there’s interesting stuff down there.”
Most of the researchers on board weren’t interested in what they might find on the sea bottom. Their priority was to collect water samples at different places and depths in the Amazonian plume to measure characteristics like acidity, temperature, salinity, and composition, as well as trying to understand what sorts of microorganisms live there.
The only researchers involved in the search for a reef at the mouth of the Amazon were Rodrigo Moura and a masters student of his, Nara Lina de Oliveira. They would have a day and a half to collect their samples at the end of the expedition, at a point when the ship would already be heading back (the trip was set to last 16 days). But the pair wouldn’t be twiddling their thumbs while the other researchers were working. Throughout the entire expedition, they’d monitor the depth, relief, and texture of the sea bottom in order to determine where they’d try their luck when the time came.
Moura and Oliveira relied on a simple method to sound the depths: they would put out a dredge, a sort of large metal bucket with claws that scrape the sea floor and pick up whatever’s in its path. It would be dragged for 5-10 meters, and the scientists would try to imagine what sort of environment might be down there based on what it brought up.
When she’d finished her measurements, 11 days after they’d set off, Yager asked Moura where they should go next. He had precise coordinates he wanted to try, based on the data they’d gathered during the trip. But Yager couldn’t get her mind off the old hand-drawn map that Moura had shown her back at the start, where each point represented a circle 40 kilometers in diameter. Her Brazilian colleague seemed to be looking for a needle in a vast marine haystack.
The dredge was put down for the first time at 4 p.m. on July 24th, a Tuesday. Yager recalled that it was a beautiful dusk, and that a sizeable number of researchers were on the deck when the contents were brought up. As many saw it, looking for a reef at the mouth of the Amazon was nothing more than a quixotic idea of Moura’s. “None of us really believed that he was going to get anything,” Yager confessed.
Moura couldn’t have picked a better spot to put down the dredge. Along with the mud came colorful sponges, corals, and fishes. Researchers and crew alike dropped what they were doing to admire the spoils. “They were the most beautiful things I’d ever seen on the sea floor,” Yager recalled, awestruck. As he recounted the episode, Moura had a triumphant smile on his face. “We hit the reef on the nose.”
The researchers observed that the life forms varied as they moved from region to region. The north section of the mouth, where the current took the bulk of the river water, had the least biodiversity. Sponges were the clear majority there. To the south, where the water is clearer, they netted corals. They found a profusion of calcareous nodules of red algae both there and at the center of the river mouth. It seemed that these small, irregular structures – which researchers call rhodoliths – were the most common formations on the seabed, as is the case with certain reefs.
While earlier expeditions had identified organisms associated with reef environments, this mission had hit upon the very organisms that could build a reef. Nobody had paid much attention to Moura’s idea. It did now seem, however, that there was indeed a reef lurking below that dense-looking, brown water.
For Moura and Oliveira, the material that had just arrived on deck was only the start of their work. Taking turns sleeping, they spent the following days coordinating the dredges and classifying the samples they turned up. “You get all sorts of organisms in with the sediment. It’s a real mess,” said Moura. After an initial washing, the material was separated out into trays designed to hold each type of organism. “Sponges go in alcohol, dried calcareous algae go in silica,” Oliveira explained. “We had to number and photograph everything.”
Given space limitations, the Brazilians couldn’t bring everything they’d collected. Oliveira said that they kept the most significant specimens from their major groups and regretfully discarded the rest. Even so, they set off for Brazil loaded down with material. For a long time, Moura hung on to the boarding pass with the stub for the 30 items he’d checked on the plane to Rio.
The expedition set out in late September of 2014, a time of year that provides optimal tide and current conditions for navigating across the mouth of the Amazon. The Cruzeiro do Sul set out from Belém and headed into the Atlantic along the river delta, on a week-long journey with 11 researchers on board. Now they had fishing nets custom-made to deal with the irregular shapes of the reef, with resistant netting that would allow them to take in many times more organisms. The material arrived in hauls that weighed around a metric ton each. One photo, which Moura later had framed, shows him marveling at a net bulging with a rainbow of sponges and calcareous formations just hauled out of their habitat, enough to fill a dumpster.
Sensors taken along on the ships allowed them to map the size and shape of the reef. Researchers were able to identify large, widely spaced eroded calcareous structures, up to 30 meters tall and 300 meters long. They estimate that the reef covers 9,500 square kilometers, an area roughly the size of Cyprus, at depths varying between 30 and 120 meters. It lies at an average distance of 150 kilometers from the coastline, and runs for around 1,000 kilometers, from Brazil’s border with French Guyana to the state of Maranhão.
Still, nobody had gone to see the reef itself. The samples they’d collected were the most tangible evidence of its existence. On the 2014 expedition, researchers had brought a small unmanned submersible that could film the reef, but wound up deciding against sending it into the cloudy, roiling waters of the river mouth. “Because of the tides, the water level can vary 8 meters in a day,” Moura said. “You can’t run the risk of losing a piece of equipment that cost R$1 million [US$ 320,000].” After the robot, the next step would be to send a diver. “The very last thing you put into the water is a human being.”
Biologist Gilberto Amado Filho pointed to a photograph on his computer, showing a rhodolith collected at the mouth of the Amazon, 120 meters deep. The image was of a flattened structure stained multiple hues of green and pink. “Whatever’s reddish is alive,” Amado Filho explained. “It’s carrying out photosynthesis, so at some point there’s definitely got to be light there.” The red algae can make use of the last remnants of sunlight that filter through the plume. They take in blue light, which is at the end of the visible spectrum. “They’re adapted for life in an extremely low-light environment,” the biologist explained.
In the Brazilian group, Amado Filho specializes in the study of the algae that constructed the massive calcareous structure in the estuary. A researcher at Rio de Janeiro’s Botanical Garden, he likes to say that he works with plants that make stones. Red algae, he explained, grow in layers, one on top of the next, and secrete calcium carbonate that accumulates irregularly, forming nodules that may grow to the size of a mango. They sometimes shift with the currents, but can also fuse and form larger structures. The algae that make them belong to the Rhodophyceae class – hence the name “rhodoliths.”
“This stone gives rise to a little calcareous condominium,” Amado Filho explained, pointing to a nodule. “The edifice is completely porous, and the cavities provide shelter for a whole range of associated biodiversity.” It becomes home to a host of mollusks, crustaceans, and other invertebrates, as well as fishes and sponges, which find in the calcareous structure a surface upon which to settle. The rhodoliths are the predominant formation at the mouth of the Amazon, and red algae are their chief engineers. Amado Filho pointed out that it would be inaccurate to call the structure a coral reef, even though it has coral on it. “It’s a kind of coralline reef called a rhodolith bed.”
Calcareous algae aren’t the only residents of the ecosystem able to get along in an extremely dark environment. The area is also home to microbes which, in the absence of light, can produce energy from molecules such as ammonia in a process called chemosynthesis. Fabiano Thompson, an oceanologist from the state of Rio Grande do Sul who heads up a laboratory at UFRJ, has taken on the task of understanding what sorts of microorganisms occur in seawater. After analyzing the DNA of microorganisms found in samples taken from below the Amazonian plume, his team identified the genes they used to carry out chemosynthesis. “The mechanism sustains the microbes, which then feed the sponges,” Thompson said.
Brazil has the largest rhodolith bed in the world, a fact unknown until few years ago. It came up when Brazilian researchers turned their attention to the region of the Abrolhos archipelago. The reefs in this iconic national park had already been quite well studied, but not the area around them – nautical maps referred to the seabed as being gravel. “Everyone was only interested in the reefs that pose a risk to navigation, the ones that go all the way to the surface,” Rodrigo Moura explained. “But we started seeing that around them, there were many more deep reef formations.”
A mission to the area revealed a rhodolith bed the size of Israel. The discovery came out in a 2012 paper published in PLOS One, authored by Amado Filho, Moura, Thompson, and colleagues of theirs. Moura noted that the discovery had multiplied the area of known reefs in Abrolhos twentyfold, but that most of them lay outside conservation zones. He was shocked by the prevailing ignorance about the region, which has been studied since the 19th century. “The rhodolith beds are the largest component of the seabed on Brazil’s continental shelf, and we’re not even remotely familiar with them,” he lamented.
Gilberto Amado Filho called attention to an important function performed by rhodoliths. The carbon that goes into the calcium carbonate secreted by red algae comes from carbon dioxide molecules dissolved in the sea. CO2, of course, is the main gas responsible for the greenhouse effect causing climate change, and much of the gas released into the atmosphere winds up in the oceans. “The algae are stocking the carbon gas from the atmosphere into a reef structure,” he explained.
When calculating the amount of calcium carbonate stored in the rhodoliths at Abrolhos, Amado Filho arrives at a number on the same order of magnitude as estimates for the largest submarine calcareous deposits in the world, including the Great Barrier Reef in Australia.
But the carbon is stored in a fragile form in the rhodolith beds and other sorts of reefs. As the oceans absorb more CO2, they become more acidic, in a phenomenon intimately connected with global warming. The outlook on this front is not favorable. If projections for increased seawater acidity by the end of the century hold out, then rhodolith beds run the risk of dissolving like so many Alka-Seltzer tablets.
Until that happens, the Amazonian formation can help us understand how reefs will react to global warming. Rodrigo Moura observed that the Amazon reef is in waters that are more acidic than normal, given the lower pH of the river water. Oxygen levels are also lower, and the water is cloudier. “And these are the conditions that we predict will intensify as the climate changes,” he noted. “The Amazonian reef is a window through which we can look at how these ecosystems will behave in the future.”
The newly discovered reef is located squarely on the latest front of expansion of oil production in Brazilian waters. The country’s equatorial coast is home to most of the 300 oil and gas exploration blocks offered up in a 2013 auction by ANP, the federal agency that oversees the industry. A dozen of them were licensed in the Amazon Mouth Basin – a marine area the size of Ecuador that stretches from the northern coast of Amapá to Marajó Island. They went to a number of companies, but commercial oil extraction has yet to begin in the basin.
In the 1970s and ‘80s, Petrobras sank dozens of wells there, but failed to find much of anything. Interest in the region waned, but grew again in the early 2010s as large oil and gas reserves turned up in waters near French Guyana as well as off the coast of Ghana, which once abutted Brazil. Given studies that showed geological similarities between these two regions and the Amazon Mouth Basin, oil companies started seeing it as promising.
One 2012 study from the United States Geological Survey calculated that the area might contain nearly 700 million barrels of oil, a modest reserve. Around the time of the 2013 auction, one ANP geologist estimated that the region might have much greater potential, somewhere around 14 billion barrels. Economist Adriano Pires pointed out that this would make the region comparable to the Libra oil field, off the coast of the state of Rio de Janeiro, where an “unfathomable” amount of oil – in the words of the ANP director at the time – was recently discovered.
The difference between the two is that extracting oil at the mouth of the Amazon is much more expensive and complex than off the coast of Rio, Pires went on to explain. He is a partner in a consulting firm that works in the energy industry, the Brazilian Infrastructure Center. “Exploration costs are extremely high, since the reserves aren’t close to ports or infrastructure,” he wrote in an email. Pires also noted that the area is environmentally delicate, and lacks the logistical infrastructure to deal with accidents.
An oil spill there could have severe effects on the environment. The waters in question lap at the edges of the largest equatorial forest on the planet and the largest mangrove ecosystem on the Brazilian coast, in the state of Amapá. Manatees, turtles, migratory birds, and countless threatened species pass through the area. The confirmation of a reef on the seafloor makes the situation even more delicate.
Foreign studies have already concluded that rhodolith beds may be buried by the detritus produced in oil drilling. In Brazil, these formations aren’t understood well enough to determine to what degree they would be affected by oil extraction – this according to a 2014 report by IBAMA (the Brazilian Institute of the Environment and Renewable Natural Resources) and IBP (the Brazilian Institute for Oil, Gas, and Biofuels), which represents the industry. At the Amazon Mouth Basin, there’s no overlap between the reef and the exploration blocks auctioned off in 2013. Certain blocks in the Barreirinhas Basin, however, on Brazil’s northeastern coast, are situated in part on rhodolith beds.
Drawing up a description of the ecosystems that exist in the areas they plan to explore is one of the requisites that IBAMA has imposed on oil companies in order to obtain licensing for the Amazon mouth. But researchers see the companies’ efforts so far as insufficient. “How can you have dozens of blocks at various stages of licensing and not see that there’s a reef there?” Moura wanted to know.
In fact, companies active in the region had come across signs of a reef, as IBP recognized in a statement to piauí. “Studies from the 1980s identified the formations, which were included in the Environmental Impact Study drawn up as part of the process of environmental licensing for offshore exploratory drilling,” the institute wrote. But the discovery was kept so low-profile that the reef would only be described in scientific literature in 2016.
Requests for environmental licensing for offshore oil extraction go through an office building in downtown Rio de Janeiro, at IBAMA’s Central Oil and Gas Office. Environmental analyst Alexandre Santos de Souza, who is among those responsible for evaluating requests, said in an interview in October that IBAMA does not permit drilling in areas with rhodoliths. “We’re requesting that companies map the sea bottom with equipment able to detect alterations in texture that signal reef formations.”
The ban on drilling in rhodolith beds doesn’t mean that the ecosystem is safe from an oil spill at a nearby rig. Itagyba Alvarenga Neto, another IBAMA analyst who evaluates environmental licensing requests, called attention to the fact that the greatest threat doesn’t lie in the Amazon mouth itself, but in the neighboring Pará-Maranhão and Barreirinhas oil fields. If there were any oil spill there, he said, the main currents might carry the oil into the vicinity of the reef. Alvarenga Neto said that IBAMA would call for companies active nearby to implement measures that would lower the risk of affecting the region, but admits that the relevant licenses will not be evaluated immediately.
Three of the companies that won the 2013 auction – Total, BP, and Queiroz Galvão – requested permission from IBAMA to drill exploratory wells in the Amazon Mouth Basin so as to evaluate the reservoirs’ potential size. The blocks in question are in ultra-deep waters, 2,000 meters down, and far from the area occupied by the Amazonian reef. All three companies have submitted the impact studies on the impact that drilling activity might have on the region. IBAMA has already reviewed Total’s. “There were gaps that needed to be cleared up, and we replied with a series of additional requests,” Alvarenga Neto said.
The same happened with the document detailing the environmental diagnosis of the region, which was drawn up by the three oil companies. In a 38-page report evaluating the submitted study, an IBAMA team ran down all of the omissions they identified, and criticized the applicants like a teacher reprimanding a careless student. “It is astounding that the companies submitted an incomplete study at a point at which they were still collecting data in the field and only presented an appendix five months later, during which time the first document was still being analyzed by the team,” read the conclusion of the report, which was authored by Souza, Alvarenga Neto, and five other IBAMA employees.
In a statement, IBP claimed that IBAMA routinely requests clarifications in the process of licensing oil and gas extraction, and underscored the pioneering nature of their environmental study of the region, which was carried out by Brazilian firms on the cutting edge of environmental diagnosis in collaboration with universities and research centers. Finally, the document asserted that the study “was done with the specific aim of backing up the assessment of the impact of planned drilling, and did not seek to fill in every lacuna in current knowledge of the region.”
The reef found at the mouth of the Amazon isn’t the kind we’re used to seeing in nature documentaries, with white-sand beaches and crystal-clear water. David Obura, a coral ecologist who directs a marine biology institute in Kenya, pointed out how history can influence researchers’ expectations. “Our interest in coral reefs began when Charles Darwin studied those sorts of organisms in the clear waters of the Pacific, and maybe that’s why we only expected to see this sort of formation in environments with limpid water,” he said in an interview in September. “But recent discoveries have shown there are reefs in environments with lots of sediment.”
In the Amazon, evidence for the existence of the reef had been building up, in spite of the oil industry’s extreme discretion. In a study published in 2015, biologist Ralf Cordeiro and three of his colleagues investigated the records of all the animals collected in expeditions to the region over the course of the previous century. They visited scientific collections, read travel logs, and came across corals and other animals typically found near reefs. Without having to leave dry land, they concluded that there must be deep reefs near the river mouth. Cordeiro, a PhD student in animal biology at the Federal University of Pernambuco (UFPE), was excited to see his team’s conclusions vindicated by the discovery of the reef. He called attention to the multidisciplinary bent of the study, which he didn’t participate in. “They drew up a complete description of the environment and explained how the Amazonian plume behaves and how it influences the reef,” he said. “The study answers a question that had been hanging in the air for 40 years.”
At the same time, the study also raises a number of questions that may guide a fuller understanding of the new reef. For a start, scientists will have to conduct more detailed surveys of the topography of the seabed – the two expeditions covered less than 10% of the area covered by the reef. They also want to know if the rhodolith beds are connected to the coral reefs in the Caribbean, to the north, and Brazil’s northeastern coast, to the south; and they’ll have to confirm if these formations are indeed serving as habitat corridors for certain species, as they suspect. Finally, researchers need to better evaluate how much carbon the rhodoliths are absorbing, and how they’re responding to rising temperatures and ocean acidity.
These questions are set to be tackled on upcoming expeditions. Carlos Eduardo de Rezende, the marine biologist at the State University of Northern Rio (UENF) who headed up the research project dedicated to the Amazonian reef, had planned a scientific voyage for December, with the aim of studying how the Amazon plume merges with the ocean. “We want to study the process in detail, since it was only broadly described in the first missions,” Rezende said. “But we’re not going to access the reef on this trip.”
Rodrigo Moura, for his part, is looking ahead to September 2017, when he aims to set out for 20 days with 12 researchers to study the new ecosystem. His plan is to rent a trawler and head out from the coast of the state of Maranhão, around Parcel de Manuel Luís. This time, he hopes to probe the system with a robot – a remotely operated submersible with a yellow hood that’s stored under a workbench in his laboratory. Equipped with a camera that can film in low light conditions, the device can obtain the first images of rhodoliths in their own habitat. Moura believes that it will be possible to send divers down; he’s volunteered to go himself.
The Amazon reef is an even more startling case, since it’s not a species, but an entire ecosystem just off the coast of Brazil. As Rodrigo Moura sees it, the find speaks to our ignorance of the entire continental shelf. “It’s like an undiscovered Atlantic rainforest, down on the sea floor,” he said. “How could we have no idea there was a mega-habitat that size there?”
Of the Brazilian scientists interviewed for this story, plenty credited this lack of information to the paltry support available for research, a situation only exacerbated by recent cuts to federal science funding and with recent moves to freeze spending on the sector for two decades. Fabiano Thompson of UFRJ believes that a country with a coast the size of Brazil’s should place its study as a priority. “But the current state of ocean sciences in Brazil is shameful,” he said, mincing no words. Carlos Eduardo Rezende of UENF noted that the country has far fewer researchers than are needed to study the 4.5 million square kilometers of Brazil’s continental shelf, over half of the area that the country takes up on land. “There are too few vessels and too few people trained to take on all of our oceanographic domains,” he complained.
Rodrigo Moura also attributed our ignorance of large submarine ecosystems to the difficulty in mapping them. Satellite images make it possible to create precise maps of vegetation cover and land use patterns, but can’t peer down into the depths of the sea. “The water acts like a filter,” he explained. “To survey the coverage and topography of the sea floor, you’ve got to go out there and measure with submarine equipment.”
Moura pointed out that we know more about outer space than we do about the bottom of the sea. “We have a topographical map of Mars that’s more precise than the map of the underwater parts of Earth,” he said. “Over 500 people have orbited the planet, and only three have gone into the Mariana Trench.” (The trench, which is the deepest part of the ocean, 11,000 meters below the surface of the Pacific, was last explored by filmmaker James Cameron in 2012.)
As Moura sees it, the lack of interest in the oceans also reflects our cultural conditioning. He observed that, when we wonder where we came from and where we’re going, we tend to turn our eyes skyward. But life came from the seas: all terrestrial animals are descendants of the first fish that ventured onto terra firma (possibly related to Tiktaalik, a 3-meter creature that lived something like 375 million years ago). “We don’t look to the sea floor when we think about the unknown,” he said. “God’s more in the water than in the sky.”
