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Ecology

New underwater lands

Area of coral reefs in Abrolhos is twice as large as previously thought

RONALDO FRANCINI-FILHO/UEPBSubmerged forests: reefs shelter a great variety of fish, such as the parrotfish, which is nowadays sold by fishermen RONALDO FRANCINI-FILHO/UEPB

Researchers who study the coral reefs of the National Marine Park of Abrolhos, the oldest nature reserve in the Brazilian seas, thought they had a good knowledge of the area, up until the year 2000 when local fishermen informed them that there were deep reefs not shown on the maps. They went out to look and discovered new underwater lands: the reef area known as Abrolhos doubled in size and this has enabled them to find out how this stretch of the coast was formed over the course of the last few thousand years. “This chance discovery led to an ambitious project”, tells us biologist Rodrigo Moura, the coordinator of the program Marine Management Area Science of the Brazilian branch of Conservation International (CI).

Made up of five volcanic reefs some 70 kilometers off the southern Bahia coast, the park harbors other treasures besides humpback whales, which draw tourists from July to November. There are the so-called “chapeirões” (big hats), mushroom-shaped reef structures the tops of which sometimes join and form colonnades around which circulate barracudas, groupers, moray eels and small colored fish. Half of the 16 species of coral at Abrolhos are exclusive to Brazil, such as brain coral (Mussismilia braziliensis), the main type of coral on the reefs in this area. The Abrolhos Bank, the largest collection of reefs in the Southern Atlantic, is larger than the national park’s area of 900 square kilometers. In total it covers 40 thousand square kilometers, similar in size to that found in the state of Espírito Santo, and in-depth investigations are only now beginning to get underway.

Moura’s group explored the sea floor along 100 kilometers of coastline – between the mouth of the Jequitinhonha river, in the south of the state of Bahia, and the mouth of the Doce river, in the north of the state of Espírito Santo – along 19 lines starting from the shore and continuing up to the edge of the continental platform, where the depth suddenly increases. “Traveling along each of these lines took two days”, explains geologist Alex Bastos, from the Federal University of Espírito Santo (Ufes), who took part in some expeditions in the sonar-equipped boat that produced three-dimensional images of the ocean floor.

The geologist from Ufes was surprised to find, at depths of up to 50 meters, paleo-canals formed about 15 thousand years ago, when the area that is now under the sea was land. “These channels indicate the riverbeds of that time”, he explains. The fact that they are preserved suggests that the sea level rose rapidly in the area.

The group selected points of interest in the sonar images and returned with a robot capable of filming in places that a diver would have difficulty reaching. For the first time in the area, the robot’s images showed black coral typical of deep waters, along with calcareous algae, with a calcium carbonate skeleton reminiscent of pebble. In September the researchers plan to use the robot to investigate other parts of the reefs and to dive down to a depth of 90 meters, in order to see if there is any coral at that depth. Paulo Sumida, an oceanographer from the University of Sao Paulo (USP) who is coordinating the analysis of the biological data, expects to install cameras on the reefs that automatically register one image every hour, to study the dynamics of the marine life there.

Although the ecological survey is only in its early stages, Rodrigo Moura and biologist Ronaldo Francini-Filho, from the State University of Paraíba (UEPB), have confirmed that the deep reefs house a fish biomass with a commercial value 30 times greater than that found in the shallow reefs. In an article to be published in the journal Aquatic Conservation: Marine and Freshwater Ecosystems, they compare the fish populations of deep and shallow reefs – some of which are protected and others where fishermen have free access. They observed that areas that have restrictions on fishing are richer in the large carnivorous fish, such as the grouper, in general the first ones to disappear from the fishing areas, and which take up to 40 years to become mature adult fish. The shortage of large carnivores means that fishermen start to go after herbivores, such as the parrotfish. The problem is that, without the parrotfish, algae begin to cover the reefs and the coral dies.

At present, less than 1% of the Abrolhos area is under protection. And there are no plans to preserve the deep reefs. According to Francini-Filho, 20% of each area would need to be preserved to maintain the biodiversity. Marine reserves benefit everyone. As the limits only apply to human beings, the fish population increases rapidly and many migrate up to 1,200 meters beyond the reserves, according to what has been published on-line in the journal Fisheries Research.

Even in protected areas, part of the Abrolhos coral is at risk. Francini-Filho confirmed that a bacterium – probably of the Vibrio genus, which arrived at Abrolhos in 2005 – is killing the brain coral in particular. The researchers estimate that, unless something is done, in a hundred years only 40% of the coral of this species will be left in Abrolhos. This is an optimistic estimate. If the water temperature rises by 1º Celsius because of global warming, it will take just 50 to 70 years before the Abrolhos coral disappears. When it is hotter bacteria proliferate faster and other problems appear, such as whitening, due to the death of micro algae that live inside the coral. Bringing global warming under control requires all countries to take action, but one can reduce bacteria levels by collecting and treating sewage in coastal cities.

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