Rhodolith Beds Research Articles

Monitoring deep Mediterranean rhodolith beds

Abstract The protocols available for sampling and monitoring shallow subtidal rhodolith beds (RBs) are inadequate for the deep Mediterranean analogues, and need calibration in order to attain comparable results. After reviewing the present knowledge of the specificities of Mediterranean RBs, and in the framework of the ongoing international effort for their conservation, a two‐step approach is suggested for their definition, identification, delimitation, description, and monitoring. Regional mapping should be improved, and RBs should be identified and delimited as those areas of the sea floor with >10% cover of live rhodoliths over a minimum surface of 500 m2, on 1:10000 scale. More detailed scales (at least 1:1000) should be used for monitoring selected RBs, in order to detect significant changes through time. Beside location and areal extent, the description of RBs should include the occurrence of macroscopic sedimentary structures of the sea floor, thickness of live cover, mean percentage cover of live thalli and surface live/dead ratio, cover of dominant morphologies of rhodoliths (simplified on a ternary diagram), and volumetrically important calcareous algal species. For the purpose of assessment of the ecological status and the evaluation of human‐induced impacts, quantitative data about community composition are required. The comparative assessment of ecological status and the identification of RBs of high conservation value for special protection should consider the natural geographic and seasonal/annual variability of RBs. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of the sand tilefish Malacanthus plumieri on the structure and dynamics of a rhodolith bed in the Fernando de Noronha Archipelago, tropical West Atlantic

Effects of the sand tilefish Malacanthus plumieri on the structure and dynamics of a rhodolith bed in the Fernando de Noronha Archipelago, tropical West Atlantic

Persistent natural acidification drives major distribution shifts in marine benthic ecosystems.

Ocean acidification is receiving increasing attention because of its potential to affect marine ecosystems. Rare CO2 vents offer a unique opportunity to investigate the response of benthic ecosystems to acidification. However, the benthic habitats investigated so far are mainly found at very shallow water (less than or equal to 5 m depth) and therefore are not representative of the broad range of continental shelf habitats. Here, we show that a decrease from pH 8.1 to 7.9 observed in a CO2 vent system at 40 m depth leads to a dramatic shift in highly diverse and structurally complex habitats. Forests of the kelp Laminaria rodriguezii usually found at larger depths (greater than 65 m) replace the otherwise dominant habitats (i.e. coralligenous outcrops and rhodolith beds), which are mainly characterized by calcifying organisms. Only the aragonite-calcifying algae are able to survive in acidified waters, while high-magnesium-calcite organisms are almost completely absent. Although a long-term survey of the venting area would be necessary to fully understand the effects of the variability of pH and other carbonate parameters over the structure and functioning of the investigated mesophotic habitats, our results suggest that in addition of significant changes at species level, moderate ocean acidification may entail major shifts in the distribution and dominance of key benthic ecosystems at regional scale, which could have broad ecological and socio-economic implications.

New diagnostic characters for the order Sporolithales (Corallinophycidae, Rhodophyta).

The diagnosis of the order Sporolithales is currently restricted to tetrasporangial anatomy. Until recently, there were few reports about gametangial, and more specifically carposporangial material for the Sporolithales. This study provides the first detailed observations of the anatomy of the mature carposporophyte phase from three species of Sporolithales commonly found in rhodolith beds from Brazil: Sporolithon episporum, S.ptychoides, and Sporolithon sp. Using these observations, along with previously published descriptions and illustrations from other representative species in the order, a comparison was made with the other three orders (Corallinales, Hapalidiales, and Rhodogorgonales) of the Corallinophycidae. We amend the diagnosis of the order Sporolithales to include the anatomy of the mature carposporophyte as follows: carposporangial conceptacles that lack a central fusion cell, but instead with numerous, short, one to two-celled, filaments that bear oblong terminal carposporangia that are distributed across the conceptacle chamber floor and walls.

Morphology and evolution of drowned carbonate terraces during the last two interglacial cycles, off Hilo, NE Hawaii

The eastern side of Hawaii Island is a rapidly subsiding margin dominated by drowned carbonate platforms. We present detailed bathymetric and backscatter data, remotely operated vehicle and submersible observations, sedimentological and 14C accelerator mass spectrometry and U/Th age data from seven submerged terraces (H7, H2a–d, H1a–b) in water depths between 1100 and 25m off Hilo, north-eastern Hawaii. The main carbonate deposits on these terraces are coral deposits, rhodolith beds, coralline algal mounds, crusts, pavements and tabular sheets. We identified five previously described sedimentary shallow- to deep-water facies and one new facies type that are consistent with reef drowning on a rapidly subsiding margin. We used palaeobathymetric data derived from the sedimentary facies, age versus depth relationships, and published sea-level curves, to estimate a uniform long-term subsidence rate of 2.80±0.36m/ky for the eastern side of Hawaii over the last 150ky. Terrace H7 developed about 380ka based on data from the western side of the island. Active coral growth on terrace H2d occurred during the Marine Isotope Stage (MIS) 6 to 5 transition, and the terrace drowned during the peak of MIS 5e when sea level rose faster than reefs could grow. Favoured by the gentle platform gradient, reefs established progressively landwards with a backstepping pattern during MIS 5e to form the terraces H2c and H2b 122ka. Final turn-off of shallow water carbonate production on terraces H2b–d coincided with the relative sea-level rise of the interstadial MIS 5a. Bathymetry and submersible data suggest that carbonate sediments on terraces H2a and H1b were deposited over an antecedent topography of local lava deltas emplaced during rising sea levels at ca. 85 and 65ka, while terrace H1a established on lava delta substrates of the Mauna Loa volcano ca. 11ka. We conclude that the initiation, growth and drowning of coral-reef terraces off Hilo differ in some ways from the pattern observed in the submerged terraces in the western side of Hawaii and that the platform evolution off Hilo is more strongly influenced by emplacement of offshore lava flows.

Sporolithon yoneshigueae sp. nov. (Sporolithales, Corallinophycidae, Rhodophyta), a new rhodolith-forming coralline alga from the southwest Atlantic

The aim of this study was to describe the new rhodolith-forming coralline alga species, Sporolithon yoneshigueae sp. nov., based on both morpho-anatomical and molecular data. Specimens were collected in rhodolith beds between 28 and 66 m depths in northeastern and southeastern Brazil. The new species can be distinguished from all other species of the genus Sporolithon by its wide tetrasporangial compartment pore diameter (35–43 µm) and the correspondingly large number (19–24) of rosette cells surrounding the tetrasporangial compartment pore. Phylogenies inferred from psbA and SSU markers support it as a new species within Sporolithon with interspecific genetic divergence varying from 8.86–10.94 %, and 3.67–4.63%, respectively. Observations from recent gathering and from herbarium collections show that specimens previously designated as Sporolithon mediterraneum in Brazil correspond to Sporolithon yoneshigueae.

Macroalgal composition and community structure of the largest rhodolith beds in the world

The Abrolhos Bank, encompassing a wide portion of the Brazilian continental shelf, harbors the world's largest rhodolith bed, which plays an important role in calcium carbonate production in the South Atlantic Ocean. Little is known about the community structure and species composition of this habitat. The aim of this study was to test the hypothesis that latitudinal differences exist in the community structure of rhodolith beds and their associated flora along the Abrolhos Bank. We sampled a total of 33 sites of rhodolith beds located in three regions—northern, central, and southern—of the Abrolhos Bank between depths of 20 and 70 m. Rhodolith density (rhod. m−2) within the beds ranged from 990 ± 347.6 to 57 ± 18.7, with mean diameter ranging from 9.4 ± 3.2 to 3.1 ± 1.4 cm. A total of 146 macroalgae species were identified, including 14 rhodolith-forming species of crustose coralline algae. Abrolhos Bank supports the world’s greatest species richness of rhodolith-forming CCA, with regional distinctiveness. Observed differences in bed structure among regions can be related to differences in shelf width, slope and depth. The studied rhodolith beds constitute a unique habitat supporting a distinctive diversity of associated organisms, and thus require special attention. We highlight the importance of local and regional differences for defining appropriate conservation strategies to protect the rhodolith bed diversity of Abrolhos Bank.

Rhodolith-forming species of the subfamilies Neogoniolithoideae and Hydrolithoideae (Rhodophyta, Corallinales) from Espírito Santo State, Brazil

The taxonomy of the rhodolith-forming species of non-geniculate coralline algae from the subfamilies Neogoniolithoideae and Hydrolithoideae (Rhodophyta, Corallinales) found from Espírito Santo State, Brazil, was evaluated based on extensive subtidal sampling. A comparative analysis of the Brazilian material to other recently described species lead us to conclude that one relatively well-known species, namely Hydrolithon rupestre, a conferatum species Neogoniolithon cf. brassica-florida and a probably new species of the genus Hydrolithon, are present in the area. All three species can be distinguished by their tetrasporangial or gametangial conceptacle anatomy. This study strengthens the hypothesis that Brazilian rhodolith beds are comparatively more diverse in numbers of rhodolith-forming species than other areas of the world.

Shelf morphology as an indicator of sedimentary regimes: A synthesis from a mixed siliciclastic–carbonate shelf on the eastern Brazilian margin

Modern shelf morphology is the result of the interplay between short and long term sedimentary processes. The relation between rates of sediment supply/carbonate growth and accommodation space creation will not only control coastal transgression and regression, but will also define the shelf sedimentary regimes acting to shape the seabed. Herein, shelf morphology and sedimentology are investigated in order to discuss how these characteristics can be representative of distinct sedimentary regimes. The study area is the eastern Brazilian shelf where coastal transgression and regression coexist with the most important coral reef system of the South Atlantic. A compilation of existing published and unpublished data was carried out in order to produce morphological and faciological maps and compare the mapped features with high-resolution seismic and sonographic data. The results show three major regions or morphological compartments: Abrolhos Shelf, Doce River Shelf and the Paleovalleys Shelf. In terms of shelf sedimentary domain, rhodolith beds predominate over the outer shelf along the entire area, coralline reefs are present along the northern Abrolhos inner shelf and a significant terrigenous mud deposit is observed associated to the Doce River adjacent inner shelf beds. The rest of the shelf is composed by bioclastic or terrigenous mud sand and gravel. Terrigenous sedimentation is always restricted to the shoreface or inner shelf shallower areas and carbonate sands and gravels are predominant elsewhere. The Abrolhos shelf shows two distinct sectors; the northern area is a typical mixed sediment environment that has a supply regime along the coast/shoreface, mainly due to longshore transport and a carbonate regime along the inner and outer shelf. The southern shelf morphology and sedimentation are controlled by the antecedent topography and is typically a accommodation regime shelf with associated rhodolith beds. The Doce river shelf is a supply regime environment with the formation of a 5–8 m thick regressive deposit with downlapping clinoforms. Southward from the Doce river shelf, a significant shift in sedimentary regime is observed as the morphology becomes very irregular with associated hardbottoms and unfilled paleovalleys. This sector of the shelf (Paleovalley shelf) is characterized by an accommodation regime. The interpretation shows that the entire study area can be defined as a mixed sedimentation shelf, showing supply and accommodation regimes. Shelf morphology worked as an indicator of these changes. Carbonate/terrigenous deposition during a highstand/regressive phase coeval along the eastern Brazilian shelf, either laterally and across shelf. This lateral/along coast variation in sediment supply and carbonate production leads to distinct lateral facies and geometry. These spatial changes in morphology and facies, with coexistence of carbonate and siliciclastic sedimentation, are very important for the correlation and interpretation of the geological record, especially stratigraphic surfaces and sequence units.

Baseline Assessment of Mesophotic Reefs of the Vitória-Trindade Seamount Chain Based on Water Quality, Microbial Diversity, Benthic Cover and Fish Biomass Data.

Seamounts are considered important sources of biodiversity and minerals. However, their biodiversity and health status are not well understood; therefore, potential conservation problems are unknown. The mesophotic reefs of the Vitória-Trindade Seamount Chain (VTC) were investigated via benthic community and fish surveys, metagenomic and water chemistry analyses, and water microbial abundance estimations. The VTC is a mosaic of reef systems and includes fleshy algae dominated rhodolith beds, crustose coralline algae (CCA) reefs, and turf algae dominated rocky reefs of varying health levels. Macro-carnivores and larger fish presented higher biomass at the CCA reefs (4.4 kg per frame) than in the rhodolith beds and rocky reefs (0.0 to 0.1 kg per frame). A larger number of metagenomic sequences identified as primary producers (e.g., Chlorophyta and Streptophyta) were found at the CCA reefs. However, the rocky reefs contained more diseased corals (>90%) than the CCA reefs (~40%) and rhodolith beds (~10%). Metagenomic analyses indicated a heterotrophic and fast-growing microbiome in rocky reef corals that may possibly lead to unhealthy conditions possibly enhanced by environmental features (e.g. light stress and high loads of labile dissolved organic carbon). VTC mounts represent important hotspots of biodiversity that deserve further conservation actions.

Fish assemblages in locations with alternative structured habitats in an eelgrass, Zostera, dominated bay: Biodiversity value and potential for refuge

The eelgrass, Zostera, is a key habitat for fish productivity in southern Australia, but it is also susceptible to major declines, as in Western Port, Victoria in the 1970s. The fish assemblages in Zostera in Western Port have been relatively well studied, but assemblages in locations with alternative habitats, and their spatial and temporal variability, have been poorly studied. This means that the ability of these locations to serve as refuge areas in periods of Zostera decline is unknown. Two primary sampling methods were used for sampling locations with alternative habitats. Underwater stereo video was used to sample locations with higher water clarity and dominated by Amphibolis, reef-macroalgae and rhodolith bed habitats. A mini otter trawl was used to sample locations with low water clarity and low relief bottom: one location was dominated by Caulerpa habitat and the other was a reference Zostera location. The results showed that many species that have previously been found to be common in Zostera seagrass were also found in Caulerpa habitat, and to a lesser extent with Amphibolis habitat. Most species were associated with multiple plant habitats although some were more specific, such as the Weedy Seadragon, Phyllopteryx taeniolatus, which was only recorded in Amphibolis habitat. Multivariate analysis indicated that fish community structure was very similar between the location with Caulerpa and the reference sub-tidal Zostera location. Smaller fish were more abundant at all locations in autumn reflecting the spring spawning period of most species. Overall, most species were not limited to associating with Zostera habitat and therefore locations with alternative structured habitats may provide a measure of refuge in the face of Zostera decline. This conclusion, however, can only be considered preliminary until there is a clearer understanding of the functional relationship between fish species and these alternative habitats. Any potential refuge value is likely to be limited for species with a specific preference for Zostera such as some pipefish species, or where species have larvae that settle primarily in shallow habitats or in locations dominated by Zostera.

Unveiling privacy: Advances in microtomography of coralline algae

Marine calcareous algae are widespread in oceans of the world and known for their calcified cell walls and the generation of rhodolith beds that turn sandy bottoms into a complex structured ecosystem with high biodiversity. Rhodoliths are unattached, branching, crustose benthic marine red algae; they provide habitat for a rich variety of marine invertebrates. The resultant excavation is relevant to sediment production, while is common that the fragments or the whole specimens result in vast fossil deposits formed by rich material that can be “mined” for biological and geological data. Accordingly, microtomography (μCT) may enable a detailed investigation of biological and geological signatures preserved within the rhodolith structure in a non-destructive approach that is especially relevant when analyzing herbaria collections or rare samples. Therefore, we prepared coralline algae samples and submitted them to a range of capabilities provided by the SkyScan1176 micro-CT scanner, including reconstruction, virtual slicing, and pinpointing biological and geological signatures. To this end, polychaetes and mollusk shells, or their excavations, coral nucleation, sediment deposits and conceptacles were all observed. Although a similar technique has been applied previously to samples of living rhodoliths in Brazil, we show, for the first time, its successful application to fossil rhodoliths. We also provide a detailed working protocol and discuss the advantages and limitations of the microtomography within the rhodoliths.

Physical forcing mechanisms controlling the variability of chlorophyll-a over the Royal-Charlotte and Abrolhos Banks-Eastern Brazilian Shelf.

The Abrolhos Bank is part of the so-called Eastern Brazilian Shelf and is an area of high ecological and economic importance. The bank supports the largest and richest coral reefs in the South Atlantic and the largest rhodolith bed in the world. The spatial and seasonal variation of phytoplankton concentration, however, and the dynamic processes controlling that variability have remained poorly known. The present study investigates the seasonal and spatial distributions of chlorophyll-a (Chl-a) and water conditions by analyzing nine years (2003–2011) of level-3 Moderate-resolution Imaging Spectroradiometer (MODIS) derived Chl-a, National Centers for Environmental Prediction (NCEP)/ETA model-derived winds, NCEP model-derived heat fluxes, thermohaline and velocity results from the Hybrid Circulation Ocean Model (HYCOM) 1/12o assimilated simulation. The results show that low/high concentrations occurred in austral spring-summer (wet season)/autumn-winter (dry season), with the highest values observed in the northern portion of the Abrolhos Bank. The typical meteorological and oceanographic conditions during austral summer favor the development of strong stratification. These conditions are 1) N-NE winds that favor an upwelling-type Ekman circulation; 2) coupling between the open ocean and the continental shelf through the western boundary current, which promotes cooler subsurface water to rise onto the shelf break; and 3) positive net heat flux. In contrast, the S-SE winds during autumn are in the opposite direction of the predominant current system over the Abrolhos Bank, thus reducing their speed and inducing an inverse shear. The warmer ocean and a somewhat cool and dry atmosphere promote the evaporative cooling of the surface layer. The above processes drive mixed layer cooling and deepening that reaches its maximum in winter. The blooming of phytoplankton in the Abrolhos Bank waters appears to be regulated by changes in the mixed layer depth, with Chl-a levels that start to increase during autumn and reach their peak in June-July.

Lithophylloideae and Mastophoroideae (Corallinales, Rhodophyta) from the Brazilian continental shelf

Brazilian continental shelf is rich in rhodolith beds and it has a relevant role as a critical ecosystem for conservation. However, we do not know the taxonomy of the rhodolith forming species and because of that we analysed samples from the REVIZEE project in which morpho-anatomical analysis was used to identify Lithophylloideae and Mastophoroideae species. We found Titanoderma pustulatum; Lithophyllum stictaeforme; Lithophyllum corallinae, Hydrolithon breviclavium, Hydrolithon onkodes and Spongites fruticulosus. This is the first detailed description of T. pustulatum from Brazil and S. fruticulosus from the Atlantic Ocean, the first record of H. breviclavium in the Atlantic Ocean and of H. onkodes in Brazilian water. L. corallinae was found 250 m deep—that is a new Coralline algae depth record for Brazilian waters. This study contributes to the understanding of the diversity in Brazilian continental shelf and indicates the importance of future systematic studies. This knowledge is relevant to guide conservation programs and evaluation of impacts.

New Insights into the Genus Lithophyllum (Lithophylloideae, Corallinaceae, Corallinales) from Deepwater Rhodolith Beds Offshore the NW Gulf of Mexico

Hard bank rhodolith beds at 45–80 m depth offshore Louisiana in the Northwestern Gulf of Mexico harbor a diverse community of non-geniculate coralline algae spanning multiple lineages including both rhodolith-forming (biogenic) taxa and others encrusting autogenic rhodoliths. Identifying these members of the Corallinales to the correct genus and species is an ongoing process because many available names need to be validated by comparison to historical type specimens. A phylogenetic analysis of concatenated plastid (psbA), nuclear (LSU rDNA), and mitochondrial (COI) DNA sequences of non-geniculate corallines belonging to the subfamily Lithophylloideae (Corallinaceae), including newly generated sequences from recently collected specimens dredged at Ewing and Sackett Banks following the April 2010 Deepwater Horizon oil spill, reveals at least two distinct species of Lithophyllum sensu lato for the region. Scanning Electron Microscopy confirmed the presence of vegetative characters congruent with those for both Lithophyllum and Titanoderma. Lithophyllum is a newly reported genus for the northern Gulf of Mexico. The generic boundaries within the Lithophylloideae are addressed in light of possible evolutionary progenetic heterochrony that may have occurred within this subfamily.

Phylogenetic analysis of rhodolith formation in the Corallinales (Rhodophyta)

Although the ecological importance of rhodolith (maerl, free-living coralline algae) beds is well-known, rhodolith-forming species have been neglected in molecular phylogenetic studies. This is the first molecular systematic study aimed at understanding whether the rhodolith habit is a fixed feature in lineages and determining the relationship (phylogenetic vs. environmental) between rhodolith and crustose habits. Phylogenetic relationships of rhodolith-forming species and encrusting coralline algae at generic and species levels were analysed using SSU rDNA and psbA sequences. Extensive sampling in the European North Atlantic, Pacific and Caribbean Mexico of Phymatolithon, Lithothamnion, Lithophyllum and Neogoniolithon taxa forming rhodoliths and crusts was accompanied by examination of type or topotype material. Phylogenetic reconstruction showed that Neogoniolithon contained a monophyletic group of rhodolith-forming species whereas other rhodolith-formers were closely related to encrusting forms in the genera Phymatolithon, Lithothamnion, Mesophyllum, Hydrolithon, Spongites and Sporolithon. DNA analysis showed that the crust-forming Lithophyllum cf. incrustans/dentatum also forms rhodoliths with a stone nucleus that occur on rocky shores. In contrast, species that form beds of non-nucleate rhodoliths (e.g. Neogoniolithon spectabile, N. strictum, Lithophyllum cf. incrustans/dentatum or sp. 1 and Phymatolithon calcareum) rarely form crusts. The rhodolith habit cannot be used to delimit species for taxonomic or identification purposes. Extensive taxonomic revision will be required to deal with problems such as the position of specimens identified as Lithophyllum margaritae in two unrelated lineages.

Paleoecology and dynamics of coralline dominated facies during a Pleistocene transgressive–regressive cycle (Capo Colonna marine terrace, Southern Italy)

The Upper Pleistocene deposits of Capo Colonna marine terrace (Calabria, southern Italy) contain a volumetrically important record of red algal facies developed during a transgressive–regressive cycle, well-expressed along a nearshore–offshore transect. This setting presents an ideal opportunity for the acquisition and interpretation of paleoecological information on coralline-dominated deposits and their response to relative sea level changes. The Capo Colonna deposits include rigid build-ups, rhodolith accumulations, and a maerl bed. The build-ups, identified as a fossil example of the present day Mediterranean coralligenous, are primarily formed by Mesophyllum alternans and, subordinately, by Lithophyllum stictaeformae, Titanoderma pustulatum and Lithothamnion sp., rarely alternating with encrusting bryozoans. Fruticose praline rhodoliths occur in a packstone bed, up to 160cm thick, 2 to 5cm in size and composed of Lithothamnion sp., Mesophyllum sp., and rare T. pustulatum. The maerl bed is about 60cm thick and laterally continuous for several tens of meters, and consists of interlocked unattached red algal branches of the species Lithothamnion corallioides, Phymatolithon sp., Lithophyllum sp., and Lithothamnion sp. The lateral distribution along the shelf profile of different red algal facies was influenced by transgressive–regressive trends. While praline rhodoliths and the maerl bed developed on mobile substrates mostly during the early highstand, respectively at intermediate and distal shelf sectors, the Mesophyllum-dominated coralligenous build-ups continued to grow for most of the regressive phase, progressively occupying all the preserved paleoshelf profile during sea level fall and resulting in a characteristic ecological vertical succession of crustose algae facies in the distal segment of the transect. Differences in substrate types determined variability in the coralligenous morphologies, with dome to mushroom shapes starting from discontinuous blocks of a basal conglomerate, and WE elongated platforms developing from a hardground and from rhodolith beds. Eventually, the development of red algal deposits became in itself the dominant control on substrate type. The red algae rich deposits of Capo Colonna marine terrace not only suggest a relationship between available substrate and geomorphological expression of the coralligenous build-ups, but also provide a framework for the paleoecological interpretation of other Neogene and Quaternary rhodalgal deposits from the Mediterranean region.

Microbial community diversity and physical-chemical features of the Southwestern Atlantic Ocean.

Microbial oceanography studies have demonstrated the central role of microbes in functioning and nutrient cycling of the global ocean. Most of these former studies including at Southwestern Atlantic Ocean (SAO) focused on surface seawater and benthic organisms (e.g., coral reefs and sponges). This is the first metagenomic study of the SAO. The SAO harbors a great microbial diversity and marine life (e.g., coral reefs and rhodolith beds). The aim of this study was to characterize the microbial community diversity of the SAO along the depth continuum and different water masses by means of metagenomic, physical-chemical and biological analyses. The microbial community abundance and diversity appear to be strongly influenced by the temperature, dissolved organic carbon, and depth, and three groups were defined [1. surface waters; 2. sub-superficial chlorophyll maximum (SCM) (48-82 m) and 3. deep waters (236-1,200 m)] according to the microbial composition. The microbial communities of deep water masses [South Atlantic Central water, Antarctic Intermediate water and Upper Circumpolar Deep water] are highly similar. Of the 421,418 predicted genes for SAO metagenomes, 36.7 % had no homologous hits against 17,451,486 sequences from the North Atlantic, South Atlantic, North Pacific, South Pacific and Indian Oceans. From these unique genes from the SAO, only 6.64 % had hits against the NCBI non-redundant protein database. SAO microbial communities share genes with the global ocean in at least 70 cellular functions; however, more than a third of predicted SAO genes represent a unique gene pool in global ocean. This study was the first attempt to characterize the taxonomic and functional community diversity of different water masses at SAO and compare it with the microbial community diversity of the global ocean, and SAO had a significant portion of endemic gene diversity. Microbial communities of deep water masses (236-1,200 m) are highly similar, suggesting that these water masses have very similar microbiological attributes, despite the common knowledge that water masses determine prokaryotic community and are barriers to microbial dispersal. The present study also shows that SCM is a clearly differentiated layer within Tropical waters with higher abundance of phototrophic microbes and microbial diversity.

Range extension and morphological characterization of rhodolith-forming species (Corallinales, Rhodophyta) from shallow water in the Mexican South Pacific

Living rhodolith beds are widely distributed along the Eastern Pacific ocean. Despite their widespread distribution, little is known about the rhodolith-forming species from shallow water in the Mexican South Pacific. Many taxonomic and morphological studies about rhodoliths have been carried out in the Gulf of California, where the forming species belong to the Hapalidiaceae and Corallinaceae families. This paper is the first report on the occurrence of the rhodolith-forming Hapalidiaceae species Lithothamnion muelleri and Phymatolithon repandum at three sites in the Mexican South Pacific. The branch density, maximum length and sphericity were measured for each determined species. Rhodoliths were distributed between 4 and 6 m depth, but differences in the branch density between species and sites were not found. Finally, the present record of L. muelleri fills the gap in the species distribution along the Eastern Pacific ocean, while the record of P. repandum is the first of the species in the region.

Rhodolith beds in the South-East Pacific

Rhodolith or maerl are the most common terms used for free living coralline red algae which live and produce sediments (Nelson 2009). They are common in the North Atlantic, Mediterranean, tropical West Atlantic, Gulf of California, Southern Japan, Western Australia and New Zealand (Foster 2001). Rhodolith beds reach the deepest section of the euphotic zone, their maximum is at approximately 286 m (Foster 2001). These beds provide habitat, refuge, settlement sites and nursery ground for a variety of marine life, but also information about past and present climate changes and represent an important economic resource used as fertilizer in agriculture (Foster 2001). Climate change, ocean acidification and fisheries have negative impacts on rhodolith beds, resulting in calls for conservation (Hall-Spencer et al. 2010). In the Eastern Pacific, rhodolith beds are known from the Gulf of California to Alaska and the Galapagos Islands, Costa Rica, and Panama. The knowledge on coralline algae along the Chilean coast is still scarce focusing on crustose and non free-living forms (e.g. Vidal et al. 2003). Here we give the first record of rhodolith beds in the South-East Pacific, based on scientific expeditions to Guarello Island (Madre de Dios Archipelago, c. 50°S 75°W), Melinka and Amita Island (Guaitecas, c. 43°S 73°W,), and Robinson Crusoe Island (Juan Fernandez Archipelago, c. 33°S 78°W). At three sites, Robinson Crusoe, Guarello and Amita, we found areas of average downward slope on rocky ground mixed with sediment spots. At depths from about 10–25 m many of these spots were covered with rhodolith beds showing a lumpy growth form in Robinson Crusoe (Fig. 1a) and fruticose habit in Guarello and Amita (Fig. 1b, c). Plants were approximately 5 cm in diameter and had one or two branches per cm in lumpy material and four to six branches per cm in fruticose material. In Melinka (Fig. 1d), rhodoliths with a lumpy growth form were found at intertidal pools. These records extend the distribution of rhodoliths and raises interesting questions about their distribution, taxonomy, evolution and ecology. Thus, rhodolith beds in the South-East Pacific need to be analyzed in detail in the future and their role in coastal processes evaluated.