Ocean Science

Where Carbonate Comes From

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Science  18 May 2012:
Vol. 336, Issue 6083, pp. 782
DOI: 10.1126/science.336.6083.782-a

Rhodoliths—a type of marine red algae that resemble corals—constitute one of the world's most voluminous shallow-water benthic communities. Though they can be found in many tropical locations worldwide, they may be most extensive on the Abrolhos Shelf off the coast of Brazil. Amado-Filho et al. conducted a detailed survey of those beds, in order to determine rhodolith distribution, extent, composition, and structure. They found that the beds cover an area of about 20,900 km2, comparable to that of the Great Barrier Reef, Australia. They estimated that the mean rate of CaCO3 production by these organisms is about 0.025 Gt/year, in line with the world's largest biogenic CaCO3 deposits, and that the rhodolith beds of the Abrolhos Shelf alone contain approximately 5% of the CaCO3 inventory of all the world's carbonate banks. Sedimentation from land-based sources and large-scale dredging and mining are the largest immediate threats to these communities, and ocean acidification presents another, longer-term danger. Rhodoliths accumulate rapidly on a geological time scale, but very slowly on a human time scale, and should thus be considered a nonrenewable resource that needs to be protected.

CREDIT: VERISIMILUS

PLoS ONE 7, e35171 (2012).

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