A reef ecosystem unlike any seen before has just been discovered at the mouth of the Amazon River.
Wedged between the French Guiana-Brazil border and the Maranhão State in Brazil, the reef lies underneath a plume of river water, helping to explain how it went undetected for so long, suggests a new study, which is published in the journal Science Advances.
For over 60 years, however, scientists have suspected that reefs might be in the region.
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Senior author Fabiano Thompson told Discovery News, "There were some studies back in the 1950s that suggested the presence of reefs, but none pinpointed the reef bodies, dimensions, locations, and compositions."
Thompson is an oceanographer and professor of marine biology at the Institute of Biology and the SAGE-COPPE of the Federal University of Rio de Janeiro. He, lead author Rodrigo Moura, and their team explored the poorly known region during three oceanographic cruises resulting from a U.S./Brazil collaboration.
Marine life found at the reef include enormous sponges, multiple types of algae, corals and related animals, hydroids (small predators related to jellyfish), spiny lobsters, at least 73 different species of fish, and other organisms. Much of the reef was made up of rhodolith beds. Rhodoliths are a type of marine algae that resemble coral.
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The scientists said that the features of the newly identified reef ecosystem deviate from those of other reef habitats classified to date. Light is very low to non-existent throughout the reef, resulting in conditions similar to those of "shadow zones." Extremely low levels of oxygen characterize such zones, which are typically hundreds to thousands of feet under the water's surface.
Another unusual feature of the reef is its location within murky, sediment-rich water. Usually reefs develop in transparent, low nutrient waters, Thompson said. In this case, however, the highly turbid Amazon -- one of the world's largest rivers -- sheds up to 333,000 nutrients per second as it flows.
Water sampling at the site also yielded an incredible number of different microbes, revealing that single-celled organisms play a central role in the reef ecosystem, which Thompson said he and his colleagues "consider to be a new biome." "Biome" refers to a community of plants and animals that occupy a distinct region. The scientists suspect that the sponges, corals and other creatures at the site could rely upon the microbes for food.
The reef and its unusual collection of marine life are already under threat. First, there are problems associated with climate change and other man-made stressors.