Brazil’s coastline may be hiding hundreds of previously unknown marine species inside rhodolith beds, underwater habitats formed by free-living nodules of calcified red algae. A recent study published in Biological Conservation identified more than 450 putative new species associated with these ecosystems, according to reporting by Gazeta do Povo.
The study used DNA metabarcoding, a molecular technique that reads genetic markers from environmental samples to identify many organisms at once. Researchers found more than 1,800 exact sequence variants among macroalgae and invertebrates, along with 21 potential new species records for the western South Atlantic.
A Hidden Marine Habitat
Rhodoliths are not corals. They are loose, often pinkish nodules built mainly by crustose coralline algae, which roll or sit on the seafloor and create hard, three-dimensional habitat for other organisms. Their beds can shelter macroalgae, mollusks, crustaceans, worms, sponges, fish and other marine life.
“Those algae beds certainly host a much greater diversity than is currently recognized,” marine biologist Guilherme Pereira-Filho of the Federal University of São Paulo (Unifesp) told CNN Brasil, according to Gazeta do Povo.
The comparison to a “pink Amazon” reflects the ecological role of these habitats rather than their appearance alone. Brazil has some of the largest known rhodolith formations in the world, including the Abrolhos Bank off Bahia, where earlier research mapped a rhodolith bed of about 20,000 square kilometers (7,700 square miles).
Why the Finding Matters
A 2014 technical report produced under a cooperation agreement between the Brazilian Petroleum Institute (IBP) and Ibama, Brazil’s federal environmental agency, described Brazilian rhodolith beds as high-biodiversity habitats that should be treated as priority areas for conservation. The report said 32 species of rhodolith-forming coralline algae had already been identified in Brazil, a richer inventory than those then known for the North Atlantic or Indo-Pacific.
The new metabarcoding study suggests that traditional surveys have captured only part of the biodiversity living in these beds. Gazeta do Povo reported that between 0.2% and 1% of all currently known marine species may occur in rhodolith-covered areas along Brazil’s coast.
That estimate comes with an important caveat: much of the biodiversity remains poorly catalogued. The authors cited gaps in genetic reference databases for Brazilian marine taxa, meaning some organisms detected by DNA may be hard to match to formally described species.
Conservation Questions
Rhodolith beds are also vulnerable. The IBP-Ibama report listed threats including marine limestone extraction, dredging, fishing, aquaculture and offshore oil and gas activity. Because the algae grow slowly, damaged beds can take very long periods to recover; the report said some rhodoliths may take centuries or even millennia to form.
The same report concluded that knowledge of Brazilian rhodolith systems was still too limited to fully support sustainable exploitation or licensing decisions in areas where they occur.
For Brazil, the new findings turn an obscure seabed habitat into a broader scientific and policy question. If the study’s estimates are confirmed, part of the country’s least visible biodiversity may lie not in forests, rivers or reefs, but in pink algal stones scattered across the continental shelf.