Santa Bárbara island (background) is the largest in Brazil's Abrolhos archipelago, home to the largest reef system in the southern Atlantic Ocean.

Overfishing, pollution, sediment runoff from coastal development, shrimp farming, oil drilling, and large-scale land conversion to agriculture are among local threats to coral reefs in the region, Conservation International Brazil scientists say.

A recent expedition found that the area's reefs cover twice the area previously estimated, spurring calls to increase habitat protection.

Scientists are now planning to study the life on the new reef structures.

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