A two-year seabed study off the eastern coast of Brazil confirmed that the Abrolhos shelf is home to the largest known continuous bed of rhodoliths in the world.
The study, which was conducted by scientists with Brazil’s National System of Biodiversity Research (SISBIOTA) and Conservation International, was published last week in the online journal PLoS ONE.
Using remote operated vehicles (ROVs), side scan sonar and SCUBA diving, the researchers measured the size of the rhodolith bed to occupy 20,902 square kilometers, an area nearly the size of El Salvador.
Sometimes mistaken as coral, rhodoliths are roughly spherical objects on the ocean floor that are made of many layers of hard red algae. Together with kelp beds, seagrass meadows, and coral reefs, rhodoliths are one of Earth’s largest seabed primary producer communities.
“Finding the largest rhodolith bed in the world on the seabed of Brazil’s Abrolhos shelf is more evidence of how important this part of the ocean is,” said Rodrigo Moura, Professor at Rio de Janeiro Federal University and co-author of the study. “Rhodoliths play a critical role in a healthy marine ecosystem by providing primary habitat that can yield diverse and abundant communities of fish and invertebrates of high commercial value.”
These unique plants build their hard layers out of calcium carbonate (CaCO3), which provides their rigid structure, gives these beds structural complexity, and enables them to create stable habitats for other species. The researchers also estimate that the rhodoliths of the Abrolhos Shelf alone accounts for approximately 5 percent of the world’s total carbonate banks.
“Rhodolith beds like this one are major carbonate factories, and could play a significant role in regulating global climate,” said Les Kaufman, a senior marine scientist with Conservation International. “But in order to understand what that role might be, and how significant a role, we must learn more about them.”
Rhodolith beds face an array of threats including ocean acidification, sedimentation from land-based sources and large scale dredging and mining. Though acidification looms the largest and cannot be managed regionally, the other threats to the health of the Abrolhos shelf rhodolith bed can be managed on a local scale. The bed falls within the Abrolhos seascape, a 9,5000 square kilometer (37,000 square miles) area of ocean where Conservation International works with the Brazilian government and community organizations to conserve and manage ocean resources.
“Based on the relatively high vulnerability of coralline algae to ocean acidification, the rhodolith beds are likely to experience a profound restructuring in the coming decades,” said the lead author of the study, Gilberto Amado-Filho, a researcher at Rio de Janeiro Botanical Garden. “With the Abrolhos shelf bed producing an estimated 25 million metric tons of calcium carbonate a year, its protection and continued study should be prioritized.”
In addition to the rhodolith beds, the study also revealed huge areas of seabed covered by seaweeds, deep holes (buracas) harboring dense clouds of juvenile fishes, and deep reefs composed of corals and coralline algae. While awed by the vast size and surprise of these newly revealed seascapes, scientists have also gained a new perspective on just how precious and imperiled the reefs are that hug the coast and islands, nourishing tourism and fisheries in coastal Bahia.