Wednesday, May 9, 2012

Rhodoliths:The Under Sea Red Algae Calcium Deposits

Heard of corals, the creatures found in the ocean? And the answer is, yes! Those coelentrates that build big deposits of calcium, sometimes structures as large as Great Barrier Reef of Australia. Know about algae, the tiny little plants building deposits of calcium around themselves thus creating deposits spreading kilometers of undersea landscape!

These unique plants build their hard layers out of calcium carbonate (CaCO3), which provides them rigid structure, and gives the beds they are located in structural complexity, and enables them to create stable habitats for other species. Called  rhodoliths, these calcium deposits have been recently reported following a joint study by Conservation International and Brazilian scientists of the Abrolhos Shelf in Brazil. Rhodoliths accounts for approximately 5 percent of the world's total carbonate banks.

Undersea exploration of rhodoliths. (Courtesy: Conservation International)

Rhodoliths are colorful, unattached, branching, crustose benthic marine red algae that resemble coral

Often 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. 


 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  conducted by scientists with Brazil's National System of Biodiversity Research (SISBIOTA) and Conservation International, was published  in April 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.


According to Prof. Rodrigo Moura of Rio de Janeiro Federal University and co-author of the study the finding of largest rhodolith bed in the world on the seabed of Brazil’s Abrolhos shelf makes this part of ocean very important. "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."


"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 threats from ocean acidification, sedimentation from land-based sources and large scale dredging and mining. Acidification looms the largest and cannot be managed regionally, but the other threats to the health of the rhodolith bed of Abrolhos shelf can be managed on a local scale.


The rhodolith 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 high vulnerability of coralline algae to ocean acidification, the rhodolith beds are likely to face profound restructuring in the coming decades, believes 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", says Gilberto.


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. With the vast size of rhodoliths  revealed in seascapes, scientists are worried of dangers to the reefs  that hug the coast and islands, nourishing tourism and fisheries in coastal Bahia.

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