Leila L. Longo

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

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 ∼21 000 km2) and has one of the largest marine CaCO3 deposits (producing 25 megatons of CaCO3 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 ammonia-oxidizing 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 μmol carbon m−2 s−1), allowing the entire Abrolhos rhodolith bed to produce 5.65 × 105 tons C per day. This estimate illustrates the great importance of the Abrolhos rhodolith beds for dissolved carbon production in the South Atlantic Ocean.

Sporolithon tenue sp. nov. (Sporolithales, Corallinophycidae, Rhodophyta) : A new rhodolith-forming species from the tropical southwestern Atlantic

A new species conforming to the generic description of Sporolithon was found forming small (1–3 cm in diameter) rhodoliths at 18–75 m depth on the eastern coast of Brazil. Sporolithon tenue Bahia, Amado‐Filho, Maneveldt et W.H. Adey, sp. nov. differs from other species of Sporolithon in having a thin, primary vegetative thallus of only 45–250 μm in thickness composed of up to 20 cell layers. Sporolithon tenue can build thicker crusts by overgrowths of thalli with new hypothallia. The absence of a layer of elongate cells at the base of the tetrasporangial chambers and the shedding of senescent tetrasporangial sori are also characters that separate the new species from all other currently recognized species within the genus. Observations from recently collected material and from herbarium specimens show that specimens previously designated as Sporolithon africanum (Foslie) J. Afonso‐Carillo in Brazil correspond to Sporolithon tenue. Molecular phylogenetic analyses of psbA sequence alignments show that the new species is phylogenetically distinct within the genus Sporolithon.

Taxonomy of the southwestern Atlantic endemic kelp: Laminaria abyssalis and Laminaria brasiliensis (Phaeophyceae, Laminariales) are not different species

Two endemic species of Laminaria, Laminaria abyssalis Joly & Oliveira Filho and L. brasiliensis Joly & Oliveira Filho, from the tropical southwestern Atlantic coast have been described. The aim of this work was to determine the conspecificity of these species based on morphological and molecular analyses (ribulose 1,5‐bisphosphate carboxylase/oxgenase, large subunit (rbcL), internal transcribed spacer (ITS) and cytochrome c oxidase subunit I (coxI)). We found an overlap between the morphological characters that are considered taxonomically important for distinguishing these two species; these characters included a differing pattern of blade splitting. In the three molecular analyses, the Brazilian Laminaria specimens were grouped into one clade with maximum support. These data support the hypothesis that the individuals analyzed represent only one species, L. abyssalis. The molecular analysis also showed L. abyssalis to be sister group to L. digitata.

Seasonal changes in population structure of the tropical deep-water kelp Laminaria abyssalis

Tropical kelp populations are rare and anomalous relicts of shallow‐water populations that existed during glacial periods of cooler oceanographic climate. The endemic Brazilian tropical kelp, Laminaria abyssalis Joly and Oliveira Filho, occurred at depths below 40 m. The seasonal variations in biological aspects of L. abyssalis sporophyte populations and local variations in seawater nutrients and temperature were evaluated. A population was sampled four times between the austral spring of 2005 to winter 2006. Seasonal variations in the population structure and in the tissue content of nitrogen (N), carbohydrate and pigments were observed. Higher density (6.3 individuals m−2), biomass (7.3 kg m−2) and blade area (13 221 cm2) were observed in summer, while the highest percentage of tissue total N (1.6%), carbohydrates (32.9%) and photosynthetic pigments (chlorophyll a = 1.9% and chlorophyll c = 0.4%) were observed in spring. The highest surface area of fertile tissue in L. abyssalis sporophytes (2.36%) was recorded in winter, indicating winter as the season when more investments are made in reproduction. The highest concentrations of total N (6.3 μM) and phosphate (0.6 μM) in seawater were observed in spring and summer, respectively. Seawater temperatures lower than 20°C, which are characteristic of upwelling waters, occurred every month and were most frequent in spring and summer. We show that L. abyssalis invests more in growth in spring and summer and reaches the greatest thallus size and population density in summer. The lower abundance during winter may be related to the lower frequency of temperatures below 20°C and the local seasonal storms that cause turnover of rhodoliths, the main substrate for L. abyssalis.

South Atlantic Rhodolith Beds: Latitudinal Distribution, Species Composition, Structure and Ecosystem Functions, Threats and Conservation Status

The largest continuous latitudinal distribution of rhodolith beds occur in the South Atlantic Ocean. Up to now rhodolith beds were referred exclusively to the western portion of the South Atlantic. Here we describe the recent advances in the South Atlantic taking into account latitudinal distribution, species composition, structure and ecosystem functions, threats and conservation status. Rhodolith beds have been mapped and ecologically described from extensive areas of the continental shelf (Abrolhos Bank), seamounts tops (Vitoria Trindade Chain), insular shelfs of oceanic islands (Fernando de Noronha Archipelago) and atolls (Rocas Atoll). Thirty three species of crustose coralline algae were recorded forming rhodoliths. Despite some initiatives, the richness of fauna associated with rhodoliths in SW Atlantic is still poorly known. Specific microbiome described associated with rhodoliths indicates important role in biomineralization process. The environmental services provided by the recently described rhodolith beds (Abrolhos Banks and Vitoria Trindade Seamounts) as calcium carbonate production, increase habitat complexity, benthic diversity and associated fish assemblages justify urgent actions to protect these ecosystems.