Physiologic and metagenomic attributes of the rhodoliths forming the largest CaCO3 bed in the South Atlantic Ocean

Abstract

Rhodoliths are free-living coralline algae (Rhodophyta, Corallinales) that are ecologically important for the functioning of marine environments. They form extensive beds distributed worldwide, providing a habitat and nursery for benthic organisms and space for fisheries, and are an important source of calcium carbonate. The Abrolhos Bank, off eastern Brazil, harbors the world's largest continuous rhodolith bed (of B21 000 km 2 ) and has one of the largest marine CaCO 3 deposits (producing 25 megatons of CaCO 3 per year). Nevertheless, there is a lack of information about the microbial diversity, photosynthetic potential and ecological interactions within the rhodolith holobiont. Herein, we performed an ecophysiologic and metagenomic analysis of the Abrolhos rhodoliths to understand their microbial composition and functional components. Rhodoliths contained a specific microbiome that displayed a significant enrichment in aerobic ammoniaoxidizing betaproteobacteria and dissimilative sulfate-reducing deltaproteobacteria. We also observed a significant contribution of bacterial guilds (that is, photolithoautotrophs, anaerobic heterotrophs, sulfide oxidizers, anoxygenic phototrophs and methanogens) in the rhodolith metagenome, suggested to have important roles in biomineralization. The increased hits in aromatic compounds, fatty acid and secondary metabolism subsystems hint at an important chemically mediated interaction in which a functional job partition among eukaryal, archaeal and bacterial groups allows the rhodolith holobiont to thrive in the global ocean. High rates of photosynthesis were measured for Abrolhos rhodoliths (52.16 lmol carbon m À 2 s À 1 ), allowing the entire Abrolhos rhodolith bed to produce 5.65 Â 10 5 tons C per day. This estimate illustrates the great importance of the Abrolhos rhodolith beds for dissolved carbon production in the South Atlantic Ocean.

Monitoring deep Mediterranean rhodolith beds

“…Finally, the high species richness associated with long‐lived rhodoliths and the build‐up of their dead remains is attributed to their three‐dimensional structure (Foster et al ., ). Rhodolith beds provide a supporting service as ecosystem engineers, thus fostering complex ecological interactions (Barberá et al ., ; Nelson, ; Cavalcanti et al ., ).…”

Eukaryotic Life Inhabits Rhodolith-forming Coralline Algae (Hapalidiales, Rhodophyta), Remarkable Marine Benthic Microhabitats

“…As an essential component of photosynthetic communities, rhodoliths produce oxygen, consolidate substrata, and function as autogenic ecosystem engineers19. The deposition of CaCO 3 by marine algae is an essential process in the global carbon cycle20 and rhodoliths are recognized as foremost carbonate builders21. Furthermore, corallines are one of the major producers of dimethylsulfoniopropionate (DMSP)22, which, upon being metabolized by algal-associated bacteria, produces volatile compounds such as dimethyl sulfide (DMS).…”

Archaea in Natural and Impacted Brazilian Environments

“…Complementing those data, a more recent work, employing pyrosequencing revealed a broader distribution of Archaea in corals [28], describing the presence of Euryarchaeota (45.61%), Thaumarchaeota (42.11%), and Crenarchaeota (10.96%). A metagenomic study of rhodoliths that form the largest CaCO 3 bed in the South Atlantic Ocean revealed that Thaumarchaeota was the dominant archaeal phylum in this kind of environment [35], again reinforcing previous findings of its higher abundance in deeper marine waters.…”