The Official Magazine of the Oceanography Society

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CITATION Dybas, C.L. 2016. Ripple marks—The story behind the story. Oceanography 29(3):22–23, http://dx.doi.org/10.5670/oceanog.2016.69.

DOI http://dx.doi.org/10.5670/oceanog.2016.69

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DOWNLOADED FROM HTTP://TOS.ORG/OCEANOGRAPHY Ripple Marks The Story Behind the Story BY CHERYL LYN DYBAS

Coral Reef Discovered in an Unlikely Locale: The Amazon River’s Freshwater Plume

Where is one of the last places on Earth with coral reefs, says lead paper author The reef forms a coral complex that scientists would look for a new coral reef? Rodrigo Moura, also of Brazil’s UFRJ. reaches depths of 10 to 120 meters. Its Perhaps the mouth of the Amazon River, How was the reef discovered? Scientists calcareous algae, sponges, corals, and where huge freshwater outflows meet the from nine institutions recently conducted hydrocoral colonies have existed for Atlantic Ocean. But that’s exactly where an expedition to the mouth of the Amazon as long as 13,000 years, and provide researchers found a thriving reef complex. to map the ocean bottom. Previous stud- habitat for 73 species of fish and six “It may be an unfavorable coral reef ies in the 1970s and 1980s reported single species of lobsters. environment, but nonetheless a vibrant samples of reef-like structures. None, how- reef exists there,” says Fabiano Thompson ever, suggested the existence of a large CORAL REEF – FRESHWATER RIVER of the Universidade Federal do Rio de reef system beneath the Amazon’s plume. RELATIONSHIP RECONSIDERED Janeiro (UFRJ) in Brazil, one of several The latest expedition was primarily The reef is a continuation of the Manuel co-authors of a paper on the discovery focused on understanding the mouth of Luiz reefs in the northeastern region of published on April 22, 2016, in the journal the Amazon, says Patricia Yager, an ocean- Brazil and is a unique system, scientists Science Advances. ographer at the University of Georgia who say. Many of the Amazon reef structures took part in the research. “But Rodrigo are 300 meters long and 30 meters high. REEF IN A RIVER PLUME Moura had an article from the 1970s that “It’s a paradigm shift in geology and The Amazon’s outflow, or plume, covers mentioned reef fish along the continental biology,” says Michel Mahiques, a geolo- 1.3 million square kilometers, ultimately shelf. He wanted to try to locate the reef.” gist at the Oceanographic Institute of the reaching the Caribbean Sea. It represents Another clue: Fishing boats have long University of São Paulo in Brazil. Mahiques 20 percent of the global river discharge to plied the plume’s waters. The fishers’ led the team that mapped the seafloor the ocean. Every second, the Amazon fer- main targets are groupers and red using sonar technology. ries 175 million liters of freshwater mixed snappers—reef fish. with sediment to the Atlantic. Little sunlight The challenges of melding 1970s map A REEF FOR THE penetrates this turbid mixing zone where coordinates with modern GPS technol- TEXTBOOKS – AND THE AGES river and sea meet. The bottom is covered ogy aside, the research team ultimately “This discovery is not just about the reef with mud, and nutrient concentrations succeeded in finding the reef and retriev- itself, but about how the reef commu- vary—conditions not usually associated ing samples to confirm its existence. “We nity changes from south to north,” says brought up the most amazing and col- Yager. “That’s in response to how much orful animals I’ve ever seen on an expe- light each area receives, a result of the dition,” says Yager. Amazon plume. In the southern section,

(above) Mollusc shell covered with barnacles and other reef builders. Photo courtesy of J. Landrum (right) R/V Atlantis on the Brazil shelf. Photo courtesy of L. Willis

22 Oceanography | Vol.29, No.3 (above) Reef sample collected off the Amazon River mouth. Photo courtesy of R. Moura (left) Side-scan sonar mosaic showing numer- ous reef mounds. Swath width for one sonar pass is ~300 m. Image courtesy of M. Mahiques for example, the reef has more exposure to light, industrial activity threatens the existence so the animals are typical reef cor- of the reef system. The scientists are ask- als and other species that photosynthe- ing for a more complete environmental size for food.” assessment of the reef before “impacts Moving north, the plume’s sediment- says Thompson. become extensive and conflicts among laden outflow darkens the ocean Molecular and genetic analyses will stakeholders escalate,” Thompson says. waters. The reef transitions from likely identify new microorganisms and photosynthesizers to sponges and sponge species along the reef, the FUTURE OF A FRAGILE REEF other reef-builders that live on food biologists believe. Coral reefs are in global decline, with the plume delivers. losses of biodiversity as a result of pol- The ages of the three reef sections are REEF AT RISK lution, overfishing, warming waters, and different: 13,000 years old in the north- In spite of its recent discovery, the Amazon ocean acidification. ern section; 4,500 years old in the central reef is already at risk. “Remarkably, “The Amazon system, however, has sur- section; and 150 years old in the southern 125 exploratory blocks for oil drilling in the vived for thousands of years in conditions section. Other important characteristics, Amazon [continental] shelf were offered in that can be compared to predicted future the scientists say, are the reef’s topogra- an international auction in 2013,” state the climate scenarios,” says Thompson. “This phy, with apparent ridge-like structures in scientists in their paper, “35 of which were reef may offer important insights into the the southern section. Mud is abundant in acquired by domestic [Brazilian] and trans- decades ahead for all coral reefs.” the northern section but almost absent in national companies. In the past decade, a The researchers recommend further the central and southern sections. total of 80 exploratory blocks have been studies of the reef “related to sensitivities acquired for oil drilling in the study region. in the hydrologic cycle of the Amazon— DRAMATICALLY CHANGING VIEW OF “Some 20 blocks will soon be produc- where extreme droughts and floods are REEF ENVIRONMENTS ing oil in close proximity to the reef,” the on the increase and will influence the “The Amazon reef defies our knowledge co-authors continue, “but the environ- functioning of this novel reef system.” of the ecological balance of such environmental baseline compiled by the compa- The abundant sponges in the central ments,” says Thompson. Reefs are usually nies and the Brazilian government is still section, for example, point to a possible found in warm seas with constant salinity incipient and largely based on sparse overall shift from a coral-dominated to a levels, high light levels, and oxygen and museum specimens.” sponge-dominated reef. biomass generated by photosynthesizers. If these companies knew about the Barely discovered—and despite its At least two-thirds of the system— reef, says Thompson, “they didn’t publish longevity—the Amazon River plume reef the northern and central sections— the information broadly.” He and other has become a moment-in-time, already thrives beneath the dark waters of the researchers believe that such large-scale changing before our eyes. Amazon plume, thanks to chemosyn- thesizing microorganisms that transform minerals into food. These chemosynthesizers support a Cheryl Lyn Dybas ([email protected]), a Fellow of the International League of complex ecosystem that exists in low light Conservation Writers, is a contributing writer for Oceanography and a marine ecologist and and low oxygen levels. “Many sponges policy analyst by training. She also writes about science and the environment for National can live in these conditions, and are Geographic, BioScience, National Wildlife, Natural History, The Washington Post, Yankee, and more tolerant of dark, oxygen-deprived many other publications. waters than corals and coralline algae,”

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