The incredible Amazonian reefs. Discovery of a new marine biome.

By Vilma Homero. Source: Faperj Bulletin (http://www.faperj.br/)

The conditions under which this occurs pointed to exactly the opposite: since the dense layer of sediment on the water prevents sunlight from penetrating, and consequently photosynthesis – the basis of the food chain in tropical coral reefs – it was believed to be impossible for them to exist. But despite all these indications, some clues pointed in the exact opposite direction: in 1997, a summary presented by researchers Bruce B. Collette and Klaus Rützler at an international scientific symposium on coral reefs in Miami, United States, spoke of the presence of sponges and reef fish in the Amazon River estuary region.

In 1999, Brazilian Rodrigo Moura and colleagues also demonstrated the presence of corals at the southern mouth of the river. Studies from the Piatam Mar project also pointed to a high concentration of biogenic calcium carbonate in that area, raising the possibility of reefs in the region.

But it was only in 2011 that a team of researchers developed a project to explore the area. Now, in 2016, the existence of invertebrates, such as sponges weighing over 100 kilograms, and rhodoliths, calcareous algae that harden and, together with other species, end up forming a reef, has been confirmed. And, as the researchers found, this reef is extensive. "What we know is that they extend for at least 900 kilometers along the coast, between Maranhão and French Guiana," says Thompson.

Representative species of fish found on reefs
from the mouth of the Amazon River (Photos: Press Release)

It's all in the article "An extensive reef system at the Amazon river mouth," published in Science Advances, from the American Association for the Advancement of Science, authored by Moura, from the Institute of Biology at the Federal University of Rio de Janeiro (UFRJ), by the Scientists of Our State, from FAPERJ, Fabiano L. Thompson, from UFRJ, and Carlos Eduardo de Rezende, from the State University of Northern Rio de Janeiro (Uenf), who coordinate the project, and several other researchers from Rio de Janeiro, universities in Pará, Bahia, Pernambuco, Paraíba, Espírito Santo, São Paulo, and the United States.

“In 2012, we managed to get there on an American ship. In 2014, we returned to the region on the hydro-oceanographic vessel Cruzeiro do Sul, from the Brazilian Navy, which allowed us to expand the study area,” says Thompson, who highlights the unusual nature of the discoveries. “In addition to the gigantic sponges, more than 50 new species were sent to biologist Eduardo Hajdu, from the National Museum (MN/UFRJ), to be described,” states Thompson.

The researcher has great reason to be enthusiastic about the discovery. He explains that the new biome comprises three large, distinct layers. The first is formed by the plume of nutrients and sediments brought by the Amazon River, rich in dissolved and particulate organic matter. It is a very turbid layer, which prevents sunlight penetration and photosynthesis, and its thickness can reach 25 meters in depth. “All of this generates a dramatic change in this new biome. Without photosynthesis, there is no release of oxygen into the water. Therefore, the oxygen level in those waters drops rapidly in the first few meters of depth, reaching values ​​between 3 and 4 mL.L-1. Precisely for this reason, the idea of ​​the impossibility of the existence of reefs at the mouths of muddy tropical rivers, with a large input of sediments, as is the case of the Amazon, has always prevailed,” says the researcher. Thompson explains that this remains true for coral reefs – those formed by the accumulation of the skeletons of dead corals and which depend on photosynthesis. “But there isn’t just one type of reef. In the case of the Amazon region, the reefs in the northern sector are formed mainly by sponges and calcareous algae,” he states.

Several species of sponges collected in the region

In the next layer, the subplume, the microorganisms that live there obtain the energy they need from chemosynthesis. That is, from minerals dissolved in the water, and not from light as in photosynthesis. Minerals such as sulfur, or nitrogenous compounds such as ammonia. “Using them as an energy source, marine bacteria carry out a biochemical, cellular, and autotrophic process. In other words, with this energy, they produce their own cells and organic matter (exudates).” In turn, these bacteria and their exudates are the food source for microorganisms, sponges, mollusks, and other marine invertebrates. In the third layer, the bottom or benthic layer, sponges and other invertebrates, as well as fish and lobsters, are scattered, feeding on the bacteria in the subplume. “What caught our attention was the presence of reefs tens of meters high and over 100 meters long, spreading between 60m and 120m deep, about 100 kilometers from the river mouth,” the researcher enthuses. Thompson further explains that, since most of the 300 cubic meters/second of muddy water that the Amazon River discharges into the Atlantic Ocean is carried north by ocean currents, this makes the reef non-homogeneous. “We need to map more than 8.000 km2, since we don't know the structure and functionality of the habitats in the region.” For this very reason, he emphasizes the importance of expanding studies in that area, since the evidence of this atypical environment cannot be lost or ignored in the face of the possibility of oil exploration in the region. “We hope that the country and the state of Rio de Janeiro can increase investments in science and technology, especially in the area of ​​Marine Sciences, because these results clearly show that we know very little about our Blue Amazon,” he says.

Samples of calcium carbonate fragments and rhodoliths collected in the Amazon region

In addition to breaking paradigms, the scientists' research highlights the need for protective measures that enable the use of this marine biodiversity. "Sponges produce bioactive compounds that may have applications in biotechnology and in the production of medicines. After all, Rio de Janeiro is a pioneer in this area," says the researcher. He notes that UFRJ, in partnership with the Admiral Paulo Moreira Institute of Studies (IEAPM), and the Federal Fluminense University (UFF) offer doctoral programs in marine biotechnology, coordinated by FAPERJ's Scientists of Our State, Ricardo Coutinho and Renato Crespo Pereira. UENF also has a postgraduate program in Biosciences and Biotechnology.

According to the biologist, since the region, near French Guiana, could be a new source for the discovery of new medicines, it is also necessary to regulate ways to preserve it and maintain our sovereignty. "Our contribution to this was academic, insofar as discovering the totally atypical existence of this new biome was quite significant," he says. The issue now is that, because they are not within the limits of an environmental protection area and, on the contrary, are located in a place of intense fishing and industrial activity, the entire region becomes vulnerable. "Even more so from the perspective of oil and gas exploration projects for that area," says Thompson. As he states, researchers are far from understanding the workings of the entire system. There are numerous aspects that still need to be studied. "Precisely for this reason, we cannot afford to lose this new biome that we do not yet fully understand," warns the biologist, who intends to return to the region soon. Certainly, it will be another opportunity for new discoveries.