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

et al. (2012) Rhodolith Beds Are Major CaCO3 Bio-Factories in the Tropical South West Atlantic. PLoS ONE 7(4): e35171. doi:10.1371/journal.pone.0035171 Rhodolith Beds Are Major CaCO3 Bio-Factories in the Tropical South West Atlantic Gilberto M. Amado-Filho 0 Rodrigo L. Moura 0 Alex C. Bastos 0 Leonardo T. Salgado 0 Paulo Y. Sumida 0 Arthur Z. Guth 0 Ronaldo B. Francini-Filho 0 Guilherme H. Pereira-Filho 0 Douglas P. Abrantes 0 Poliana S. Brasileiro 0 Ricardo G. Bahia 0 Rachel N. Leal 0 Les Kaufman 0 Joanie A. Kleypas 0 Marcos Farina 0 Fabiano L. Thompson 0 Simon Thrush, National Institute of Water & Atmospheric Research, New Zealand 0 1 Instituto de Pesquisas Jardim Botanico do Rio de Janeiro , Rio de Janeiro, RJ , Brazil , 2 Instituto de Biologia, Universidade Federal do Rio de Janeiro , Rio de Janeiro, RJ , Brazil , 3 Departamento de Ecologia e Recursos Naturais, Universidade Federal do Esp rito Santo , Vito ria, ES , Brazil , 4 Instituto Oceanogra fico, Universidade de Sa o Paulo , Sa o Paulo, SP , Brazil , 5 Centro de Ciencias Aplicadas e Educac a o, Universidade Federal da Para ba , Rio Tinto, PB , Brazil , 6 Departamento de Botanica, Universidade Federal Rural do Rio de Janeiro , Serope dica, RJ , Brazil , 7 Boston University Marine Program, Boston, Massachusetts, United States of America , 8 Climate and Global Dynamics , National Center for Atmospheric Research, Boulder, Colorado, United States of America, 9 Instituto de Ciencias Biome dicas, Universidade Federal do Rio de Janeiro , Rio de Janeiro, RJ , Brazil 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 (2uN - 27uS). To quantify their extent, we carried out an inter-reefal seabed habitat survey on the Abrolhos Shelf (16u509 - 19u459S) 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 m22 yr21, with a total production rate of 0.025 Gt yr21, 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. - Funding: Funders are the Conselho Nacional de Desenvolvimento Cientfico e Tecnol ogico - Brazil, the Coordenacao de Aperfeicoamento de Pessoal de Nvel Superior - Brazil, the Fundacao de Amparo a` Pesquisa do Estado do Rio de Janeiro - Brazil, the Fundacao de Amparo a` Pesquisa do Estado de Sao Paulo - Brazil, Conservation International, USA, and The Gordon and Betty Moore Foundation, USA. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. Shallow water tropical benthic communities such as coral reefs are well known to be major carbonate producers in coastal areas [13], and significant progress has been made in understanding their calcium carbonate (CaCO3) production by mapping their global distributions [14] and by estimating mineralization rates [58]. There is growing evidence that communities dominated by crustose coralline algae (CCA) can also contribute significantly to the CaCO3 cycles of continental shelf ecosystems [911] due to their high rates of community CaCO3 production and dissolution [11]. Rhodolith beds are aggregates of nodules of non-geniculate CCA that generally occur in waters shallower than 150 m depth subjected to episodic wave or current movement, forming large expanses of hard bottom habitat [9]. Rhodolith beds stand together with kelp beds, seagrass meadows, and CCA reefs as one of the worlds four largest macrophyte-dominated benthic communities [9,12], but information on the CaCO3 production by rhodoliths remains scarce and biased toward temperate beds [13]. The global distribution of rhodolith beds is highly discontinuous, with larger concentrations recorded off southern Japan, western Australia and the Gulf of California, as well as in the Mediterranean and along Norway, Ireland, Scotland, northeastern Canada, the eastern Caribbean and Brazil [9]. Worldwide, there have been few attempts to map the large-scale distribution of rhodolith beds [9], but studies from the early 1970s suggest that those occurring off Brazil, between 2uN and 27uS, potentially represent one of the largest marine CaCO3 deposits in the world, with estimates of 261011 tons of CaCO3 [1416]. The region known as the Abrolhos Bank (16u509 - 19u459S) is a ,46,000 km2 expanse of the eastern Brazilian continental shelf; its inner and mid shelf encompass the largest and richest biogenic reefs in the South Atlantic [1719], bearing coral assemblages dominated by Brazilian-endemic Neogene relicts of the genus Mussismilia. Although CCAs are recognized as the most important component of Abrolhos reefs [1518], and rhodolith beds are recorded to the north and to the south of this region [2021], the geographic extent and role of rhodolith beds on the Abrolhos Shelf have been largely overlooked. Understanding the CaCO3 fluxes of the tropical Southwestern Atlantic hinges on accurate quantification on the extent and CaCO3 production of these large rhodolith beds. The aim of this work was thus to determine the size and CaCO3 production of the rhodolith beds within the Abrolhos Shelf. This meso-scale system may provide valuable insights on the overall role of the massive rhodolith beds of the western tropical and subtropical South American shelf. To accomplish this task, surveys using side scan sonar (SSS), remotely operated vehicles (ROVs) and mixed-gas diving, as well as in situ assays to estimate CaCO3 production were perfomed. Our analysis confirms the overwhelming importance of this CaCO3 bio-factory for the Southwestern Atlantic Ocean CaCO3 cycles. A representative SSS coverage was acquired for all habitat types of the mid and outer portions of Abrolhos Shelf. Flat and highly re (...truncated)