Rhodolith Beds Are Major CaCO3 Bio-Factories in the Tropical South West Atlantic

Abstract

Rhodoliths are nodules of non-geniculate coralline algae that occur in shallow waters (<150 m depth) subjected to episodic disturbance. Rhodolith beds stand with kelp beds, seagrass meadows, and coralline algal reefs as one of the world's four largest macrophyte-dominated benthic communities. Geographic distribution of rhodolith beds is discontinuous, with large concentrations off Japan, Australia and the Gulf of California, as well as in the Mediterranean, North Atlantic, eastern Caribbean and Brazil. Although there are major gaps in terms of seabed habitat mapping, the largest rhodolith beds are purported to occur off Brazil, where these communities are recorded across a wide latitudinal range (2°N - 27°S). To quantify their extent, we carried out an inter-reefal seabed habitat survey on the Abrolhos Shelf (16°50′ - 19°45′S) off eastern Brazil, and confirmed the most expansive and contiguous rhodolith bed in the world, covering about 20,900 km2. Distribution, extent, composition and structure of this bed were assessed with side scan sonar, remotely operated vehicles, and SCUBA. The mean rate of CaCO3 production was estimated from in situ growth assays at 1.07 kg m−2 yr−1, with a total production rate of 0.025 Gt yr−1, comparable to those of the world's largest biogenic CaCO3 deposits. These gigantic rhodolith beds, of areal extent equivalent to the Great Barrier Reef, Australia, are a critical, yet poorly understood component of the tropical South Atlantic Ocean. Based on the relatively high vulnerability of coralline algae to ocean acidification, these beds are likely to experience a profound restructuring in the coming decades.

Anatomical structure overrides temperature controls on magnesium uptake – calcification in the Arctic/subarctic coralline algae &lt;i&gt;Leptophytum laeve&lt;/i&gt; and &lt;i&gt;Kvaleya epilaeve&lt;/i&gt; (Rhodophyta; Corallinales)

“…One of the key roles of corallines is the building of carbonate substrate that underpins many ecosystems globally: for example, the thick bioherms found in coral reef structures (Adey, 1978a(Adey, , b, 1998, the extensive rhodolith beds off South American (Amado-Filho et al, 2012;Bahia et al, 782 M. C. Nash and W. Adey: Magnesium and anatomy in coralline algae 2010) and Australian (Harvey et al, 2016) shores, maerl substrate in the Mediterranean (Martin et al, 2014), and the dominant rocky benthos biostromes and rhodoliths in many Arctic and subarctic environments . There are concerns that as atmospheric pCO 2 increases and consequent ocean acidification increases, there will be negative impacts on the capacity of corallines to continue building these important substrates (e.g.…”

Echinodermata associated to rhodoliths from Seixas Beach, State of Paraíba, Northeast Brazil

“…Rhodoliths are aggregates of nodules of unarticulated encrusting coralline algae (Amado-Filho et al 2012). These structures occur in shallow waters up to depths of 150 m, forming extensive rhodolith beds and hard bottom habitats.…”

Potential and limitations of finite element modelling in assessing structural integrity of coralline algae under future global change

“…They are major contributors to the global inorganic carbon budget in shallow water ecosystems (Mackenzie et al, 2004). The largest rhodolith bed found on the Abrolhos shelf contributes roughly 5 % to the global calcium carbonate budget (Amado-Filho et al, 2012). Additionally these benthic ecosystems support a high level of biodiversity by forming structurally and functionally complex habitats (Nelson, 2009) for many organisms includ- ing polychaetes, crustaceans and mollusks (Foster, 2001), as well as being important nursery grounds to commercial species including scallops (Grall and Hall-Spencer, 2003).…”