Largest rhodolith bed

Rhodoliths are unattached forms of coralline algae (a calcifying seaweed). Along with kelp beds, seagrass meadows and coralline algal reefs, rhodolith beds are known as one of the world's four largest macrophyte-dominated benthic communities. The largest contiguous rhodolith bed is found in the South Atlantic Ocean off the coast of Brazil, along the Abrolhos Shelf (16.83°/19.75° S), covering an area of 20,902 square kilometres (8,070 square miles), which is larger than the country of Slovenia. The Abrolhos rhodolith bed could represent the highest deposit of calcium carbonate (CaCO3) in the world (more than any single coral reef), weighing as much as 2 x 10^11 tonnes in its entirety and with an estimated annual CaCO3 production rate of 25 million tonnes (27.5 million US tons).

The mean average rhodolith coverage in the contiguous bed is 69.1%, while mean density is around 211 nodules (the name for individual rhodoliths) per square metre. The rhodolith bed covers approximately 45% of the entire Abrolhos Shelf.

Rhodolith beds are generally found in shallow waters no deeper than 150 m (500 ft) where they can take advantages of currents and wave action to move around. Other large examples of rhodolith beds are located off southern Japan, western Australia, the Gulf of California and in the Mediterranean, among others, though no single bed reaches the scale of that found off Brazil.

The findings regarding the Abrolhos rhodolith bed were published in the journal PLoS ONE in April 2012.