Southwestern Atlantic Research Articles

Plastic ingestion by odontocetes from the Western South Atlantic: A particular concern to a threatened species

The ingestion of debris by marine fauna is a growing threat to biodiversity. This study aimed to evaluate and characterize litter ingestion by odontocetes from the Western South Atlantic. Between 2018 and 2022, 154 stomachs from six species were collected from stranded individuals and incidental captures. Stomach contents were analyzed with the naked eye and items of anthropic origin found were counted and physically/chemically characterized. Generalized Linear Models were used to evaluate the influence of biological factors on the presence/absence of litter in stomachs, and for Pontoporia blainvillei only, the influence of these factors on the number of ingested items was also tested; additionally, a temporal analysis of ingestion was done for this species (1994–2022). A total of 156 items, mainly macro-sized plastics made of polypropylene, were found in 52 stomachs of four species: Tursiops spp. (FO% = 3.3%), Steno bredanensis (10.0%), Delphinus delphis (28.6%) and P. blainvillei (47.5%). The presence/absence of litter was explained only by species (χ2 = 28.29 and p < 0.001). For P. blainvillei, a threatened species in the region, the number of items was positively influenced by individual size (χ2 = 6.01 and p = 0.01) and sex (χ2 = 7.93 and p = 0.005). There was an increase in plastic ingestion by this species over the years (χ2 = 121.6 and p < 0.001) and it was estimated that 75% of P. blainvillei stomachs will contain plastic by 2040. The ingestion of litter by odontocetes from the Western South Atlantic was confirmed and the potential risks posed by this type of pollution were evidenced, especially since these species also face other anthropic pressures. These results further demonstrate the increasing threat of litter in the ocean and highlight the importance of circularity of plastics and proper waste management.

New report of the rare Sciadonus alphacrucis Melo et al., 2022 (Teleostei, Ophidiiformes, Bythitidae), DNA barcoding, and range extension in the western South Atlantic.

Sciadonus alphacrucis Melo, Gomes, Møller & Nielsen, 2022 is a rare deep-sea species, previously known from only two specimens collected off São Paulo State, southeastern Brazil, in the western South Atlantic. Herein, we report a new specimen of S. alphacrucis collected on the continental slope off Santa Catarina State, southern Brazil, thereby extending its known distribution by 420 km. Additionally, we provide the new meristic and morphometric data, the molecular identification using sequences of the cytochrome c oxidase subunit I (COI), an updated distribution map, and a discussion of troglomorphic traits.

Tamoya haplonema (F. Müller, 1859) (Cnidaria: Cubozoa): indicator of tropicalization in the Southwestern Atlantic?

Tamoya haplonema has been highlighted as a species of Cubozoa with a wide distribution in the western South Atlantic coast. However, recent studies highlight its preference for cold waters and its absence in the summer months in southern Brazil, being considered as having a subtropical distribution. In recent summer seasons, strandings of this species on beaches and stings of bathers have been observed, suggesting that T. haplonema may be responding to a more favorable thermal environment for its development on the coast of Uruguay, with possible increase in its occurrences to the north of Argentina. This possible poleward displacement, if proven, may be related to several factors, including a response to the tropicalization process of the oceans that has been observed worldwide.

Life history strategy of Tubastraea spp. corals in an upwelling area on the Southwest Atlantic: growth, fecundity, settlement, and recruitment.

Over the past few decades, corals of the genus Tubastraea have spread globally, revealing themselves to be organisms of great invasive capacity. Their constant expansion on the Brazilian coast highlights the need for studies to monitor the invasion process. The growth, fecundity, settlement, and data on the coverage area of three co-occurring Tubastraea species in the 2015-2016 period were related to temperature variation and light irradiance on the rocky shores of Arraial do Cabo, Rio de Janeiro. Hence, this study sought to understand and compare the current invasion scenario and characteristics of the life history strategy of sun coral species based on environmental variables, considering the uniqueness of this upwelling area in the southwestern Atlantic. For that, we evaluate the fecundity, settlement, and growth rates of corals by carrying out comparative studies between species over time and correlating them with the variables temperature and irradiance, according to seasonality. Field growth of colonies was measured every two months during a sample year. Monthly collections were performed to count reproductive oocytes to assess fecundity. Also, quadrats were scrapped from an area near a large patch of sun coral to count newly attached coral larvae and used years later to assess diversity and percentage coverage. Results showed that corals presented greater growth during periods of high thermal amplitude and in months with below-average temperatures. Only Tubastraea sp. had greater growth and polyp increase in areas with higher light incidence, showing a greater increase in total area compared to all the other species analyzed. Despite the observed affinity with high temperatures, settlement rates were also higher during the same periods. Months with low thermal amplitude and higher temperature averages presented high fecundity. While higher water temperature averages showed an affinity with greater coral reproductive activity, growth has been shown to be inversely proportional to reproduction. Our study recorded the most significant coral growth for the region, an increase in niche, high annual reproductive activity, and large area coverage, showing the ongoing adaptation of the invasion process in the region. However, lower temperatures in the region affect these corals' reproductive activity and growth, slowing down the process of introduction into the region. To better understand the advantages of these invasion strategies in the environment, we must understand the relationships between them and the local community that may be acting to slow down this colonization process.

Diel vertical migration and seamount stepping stones promote species connectivity from coastal to offshore insular systems in the Tropical Southwestern Atlantic

AbstractThe recruitment of marine species in isolated oceanic island systems can be challenged by prevailing currents, as exemplified by the Tropical Southwestern Atlantic. In this region, the Fernando de Noronha ridge hosts several seamounts, the Rocas Atoll and the Fernando de Noronha Archipelago, which are home to great marine biodiversity. However, along the ridge, the central branch of the South Equatorial Current (cSEC), flowing westward, poses a challenge to the recruitment of organisms toward Fernando de Noronha. To unveil critical insights into the intricate processes shaping biodiversity in these insular ecosystems, we use a dispersal Lagrangian tool to explore the role of diel vertical migration (DVM) to depth strata influenced by the South Equatorial Undercurrent (SEUC), which flows eastward bellow the cSEC, in shaping species dispersal and metacommunity dynamics. Our results show that while not a direct journey, the DVM into SEUC‐influenced strata increases the possibility that the seamounts and the Rocas Atoll act as stepping stones between the continental shelf and Fernando de Noronha. Propagules of organisms originating primarily from the continental shelf are transported to the western seamounts of the ridge. Upon reaching the western seamounts, organisms can find suitable habitats to recruit. The progeny of these communities that migrate to SEUC‐influenced strata have the opportunity to reach suitable habitats at the Rocas Atoll and the Eastern seamounts, ultimately connecting to the Fernando de Noronha archipelago. These results provide scientific fundaments for the development of a functional network of marine protected areas in the Tropical Southwestern Atlantic.

Western Atlantic regionalization based on distributional congruence patterns of Scleractinian corals

Coral reefs represent a source of ecosystem services relevant for the permanence of coastal human communities. Given the importance of zooxanthellate scleractinian corals (ZSC) in these ecosystems, information on the presence and distribution of this group is valuable for studying the biodiversity and establishing management strategies to ensure their permanence over time. Despite being a highly studied biological group in the Western Atlantic, records of ZSC presence are heterogeneous and are distributed mainly in the Caribbean Sea. One way to analyze the distribution of biota at large spatial scales is through biogeographic regionalizations. To identify the distribution patterns of ZSC in the Western Atlantic and propose a biogeographic regionalization based in this biological group, we performed a Parsimony Analysis of Endemism (PAE) at ecoregion scale using Species Distribution Models (SDM) to fill the gaps in data on the distribution of these corals. Through these analyses, we identified the presence of two main biogeographic provinces: Northwestern Atlantic Tropical Province and Tropical Southwestern Atlantic. According to Jaccard Index, this regionalization is highly similar to those performed with multitaxa by other authors, which demonstrates that for these purposes this taxa can be considered as a surrogate group. In terms of management, this study highlights the importance of establishing preservation and conservation measures that address this biological group, in order to guarantee both the permanence of other taxa and the ecosystem goods and services they provide.

The Brazilian Santos basin underwater soundscape monitoring project (PMPAS-BS)

This paper describes the Santos Basin Underwater Soundscape Monitoring Project (PMPAS-BS), a Brazilian ocean soundscape monitoring initiative. The main objective of the project is to quantify and assess hydroacoustic noise of anthropogenic origin in a large sedimentary basin extending from 23° S to 28° S on the southeastern Brazilian continental margin of the South Atlantic Ocean. Noise associated with oil and gas (O&amp;amp;G) exploration and production activities is the primary target, but this oceanic region also has busy shipping lanes for commercial, military, and fishing vessels. The two main hubs of Brazil’s export and import of goods by sea are located in this region: Santos and Rio de Janeiro ports. The project has three measurement components: mobile monitoring based on gliders and drifting acoustic profilers, fixed shallow-water monitoring based on acoustic measurements at coastal stations near shipping lanes associated with exploration and production activities in the Santos Basin, and fixed oceanic monitoring based on deep-water mooring lines equipped with passive autonomous acoustic recorders near production units, shipping lanes, and areas with lower intensity of O&amp;amp;G activities (pristine or reference sites). Numerical modeling of anthropogenic underwater acoustic noise has also been included as a fourth project component. The PMPAS-BS covers an area of more than 251,000 km2 and uses several instruments with different methods and sensors for acoustic measurements. Its results provide current sound levels over a very large region of the western South Atlantic, both in areas more and less affected by anthropogenic activities.

Marine environmental variability in Northern Patagonia (Southwestern Atlantic Ocean) as recorded in Glycymeris longior shells

Certain marine regions in the world lack long instrumental records of environmental variables or such records are incomplete. This deficiency particularly applies to Argentine Patagonia, where existing instrumental records span only the last few decades. In the present study it was explored whether such data can be reconstructed from a natural archive, specifically shells of the bivalve mollusk Glycymeris longior from the San Matías Gulf, north Patagonia. For this purpose, a multidecade-long time-series was constructed using variations in the annual shell growth. The time-series spans from 1890 to 2020 and is based on shells from museum collections (live-collected from 1918, 1933 and 1945) and from scientific surveys conducted between 1989 and 2021. An analysis of the links between environmental variables and shell growth was performed between 1976 and 2020 (expressed population signal >0.85). The common signal among the growth curves of individual specimens of G. longior suggests that the growth is influenced by environmental parameters. However, the growth of G. longior did not show significant correlations with the low- nor with the high-frequency components of SST and food supply (chlorophyll-a concentration and POC), suggesting that these parameters do not limit shell growth at the studied site or were undetected with our analyses. The chronology also seems to be insensitive to regional climate patterns such as the Southern Annular Mode. The chronology has the potential for being expanded spatially and temporally.

HIGHLY BIOERODED RHODOLITHS FROM THE VITÓRIA-TRINDADE SEAMOUNT CHAIN (BRAZIL, SOUTHWESTERN ATLANTIC)

Abstract Rhodoliths are nodules mainly composed of crustose coralline algae with subordinate encrusting organisms, formed by successive overlapping encrustation. The subspheroidal rhodoliths from the Vitória-Trindade Seamount Chain (Jaseur Seamount and Trindade Island shelf; Brazil, southwestern Atlantic), sampled at water depths from 65 to 74 m, were built by crustose coralline algae (Harveylithon, Lithophyllum, Lithothamnion, Mesophyllum, Roseolithon, and Sporolithon) and subordinated encrusting foraminifera (agglutinated, unidentified hyaline, and Homotrema rubrum), bryozoans, serpulids, and balanids. Successive taphonomic phases of bioerosion, boring filling, and cement precipitation modified the original rhodolith inner structures resulting in a complex structureless mass of coralline algal fragments, encrusting organisms, borings, lithified fine-grained sediment, and carbonate cement. Borings include the ichnogenera Entobia (produced by etching sponges), Gastrochaenolites (boring bivalves) and Trypanites (polychaetes and sipunculid worms). The lithification of the material filling the borings (micrite and carbonate cements) created new substrates for subsequent bioerosion. Radiocarbon dating of selectively sampled invertebrate and algal skeletons in the rhodolith interior yielded calibrated ages of hundreds of years (up to 912 ± 152 years cal. BP on the Trindade insular shelf and up to 763 ± 131 years cal. BP on Jaseur Seamount). These values indicate growth rates from 0.1 to 0.5 mm/year, which are significantly higher than those recorded from rhodoliths at similar depths on the Brazilian shelf. Low sedimentation settings and high productivity at the tops of the seamounts and island shelf promoted the growth of nodule frame builders, both autotrophs and heterotrophs, and favored continuous activity of bioeroders.

Multiple Lagrangian Jet‐Core Structures in the Malvinas Current

AbstractThe Malvinas Current (MC) in the Southwestern Atlantic is characterized as a system of multiple Lagrangian jets. This is done by applying geodesic theory of Lagrangian Coherent Structures (LCSs) on altimetry‐derived velocity. The number and spatial disposition of jet‐cores organizing the MC are found to vary in time influenced by topographic waves propagating along the current. The Lagrangian analysis reveals that permanent jet‐cores tend to approach one another upstream, yet do not merge into a single jet as the Eulerian analysis of the data suggests. Independent support for the existence of multiple jets is provided by trajectories of surface drifters from a deployment of unparalleled dimensions for the region and ocean color images. The drifters develop the characteristic boomerang‐shaped patterns into which passive tracers straddling jet‐cores deform and exhibit Lagrangian metrics that are largely consistent with those derived from altimetry data. Ocean color imagery reveals similar “chevrons” and suggest upwelling along the jets, which is consistent with a new solution of arrested topographic wave dynamics. This observation and the finding that the MC jet system is influenced by propagating waves suggests that the MC variability may have major implications in the modulation of primary productivity on synoptic timescales. Drifters flowing into the open ocean, exhibit organizing patterns that are largely shaped by mesoscale circulation and essentially differ from those observed along the MC. Evidence of this observation is provided on the basis of LCS analysis and the calculation of a quasi‐objective Lagrangian metric derived directly from drifter trajectories.

Role of environmental factors in the genetic structure of a highly mobile seabird

AbstractAimEnvironmental features can act as selection pressures and barriers to gene flow between populations. The genetic structuring of highly mobile but philopatric seabirds creates a paradox, and the role of oceanographic and geographic variables is still poorly understood. In this study, we investigate the influence of environmental and geographic variables in the genetic and phenotypic diversity of a pantropical seabird breeding in islands and archipelagos separated by different geographic distances, up to thousand kilometres, and which differ in environmental characteristics.LocationIslands and archipelagos in the southwestern (SW) Atlantic Ocean.Taxon Sula dactylatra, Lesson, 1831 (masked booby).MethodsThe population structure of the species was accessed through mitochondrial and nuclear DNA. To test Isolation by Environment (IBE) versus by Distance (IBD), sea surface temperature, primary productivity and salinity, as well as isotopic niche based on carbon and nitrogen, and distances between colonies and from the continent, were used. We also tested the correlation between the genetic structure and the morphometry of individuals in each colony.ResultsWe uncover the presence of low genetic structure between populations. Nevertheless, differences were identified between inshore and offshore colonies, with the influence of landscape characteristics of these two types of environment. The morphometric and isotopic niche variations are consistent with this segregation.Main ConclusionsEnvironmental variables of coastal and oceanic environments seem to influence the genetic structure of masked boobies, even though it is low in the SW Atlantic Ocean, highlighting the role of environmental heterogeneity in shaping biodiversity.

Regional differences in the air–sea CO2 flux between 3 and 14°S in the south-western tropical Atlantic

Context The fugacity of surface-seawater CO2 (fCO2sw) and the sea–air CO2 fluxes in the south-western tropical Atlantic (SWTA) were studied to increase the knowledge about the carbon cycle in this region. Aims This paper aims to describe the distribution of fCO2sw in SWTA. Methods The fCO2sw was measured from 2008 to 2020 by volunteer merchant ships with an onboard system that measures pCO2 while the vessels were underway. Key results Higher values occurred north of 8°S than in the region south of 8°S. The north is a strong source of CO2 for the atmosphere, with an annual mean value of 3.14 ± 0.52 mmol m−2 day−1. The south is a weaker source of CO2, with an annual average of 0.93 ± 0.90 mmol m−2 day−1. In the months of July and August, a weak sink of CO2 was observed, with a mean of −0.55 mmol m−2 day−1. Conclusions and implications The differences between these two regions are explained by the origin of the surface-water masses encountered along the ship track. The central branch of the South Equatorial Current (SEC) transports surface water, with a higher CO2 concentration and lower salinity, north of 8°S, whereas the surface waters between 8 and 14°S come from the southern branch of the SEC. The intertropical convergence zone is another physical process influencing the region north of 8°S.

Lagrangian characterization of the southwestern Atlantic from a dense surface drifter deployment

The Southwestern Atlantic (SWA) is characterized by its large Eddy Kinetic Energy as the result of the confluence of two major western boundary currents, the northward flowing Malvinas Current (MC) and the southward flowing Brazil Current. The SWA study was addressed in the literature based on altimetry data, in situ measurements, regional models and ocean reanalysis. The present study constitutes the first effort to sample a portion of the SWA, with a dense drifter array (N = 62) deployment. The drifters, drogued at 15 m depths, were deployed across the MC and the Argentine Continental Shelf along two zonal transects located at 47°S and 47.25°S, between the 8th and the September 9, 2021. Drifters were set to deliver their position every 10 and 60 min, providing accurate Lagrangian trajectories that provide information on a large range of space and time scales of the surface currents. Three regions are clearly identified based on the analysis of the speed of the drifters, of their trajectories and of the spectral density of their velocities: the continental shelf, the slope and the open ocean. The comparison of the trajectories of the drifters with satellite altimetry images shows that, in general, drifters follow mesoscale features that are detectable in satellite altimetry maps. The analysis of the drifter trajectories also allowed us the study of submesoscale features of the flow (1–10 km) that are not observable in satellite altimetry data. Comparison with cloud-free, high-resolution color images, shows that drifter trajectories organized by the mesoscale flow might also locally follow sub-mesoscale features. In frontal regions it was found that drifter velocities double satellite altimetry geostrophic velocities, which suggests that the dynamics at those regions is largely dominated by ageostrophic components. The ageostrophic Ekman component might explain the direction of the drifters when strong winds from a given direction prevail for several days and the drifters are not in a region with large sea surface height (SSH) gradients. The joint analysis of drifters’ trajectory and SSH clearly depicts that mesoscale features on the open ocean region control the cross-shelf exchanges between the MC and open ocean regions as well as the strength and width of the MC. Finally, the spatial density distribution of the drifters during the first hours after deployment and within a small eddy also allowed us to characterize the flow in terms of its divergence, vorticity and strain, indicating that the MC is geostrophic and has a jet-like behavior while the eddy is largely ageostrophic and has a dominant vorticity component over strain. We conclude observing that the analysis of a dense array of drifters provides valuable information of the flow that cannot be attained solely based on satellite data.

Quaternary fossil diversity of stingrays (Chondrichthyes: Myliobatiformes) from the eastern coast of South America, Brazil, southwestern Atlantic

Sharks, rays, and chimeras have a limited fossil record compared to other taxa due to their predominantly cartilaginous skeletal structure. Fossilization tends to preserve anatomic structures such as teeth, scales, cephalic and caudal fins, and other fins. The Myliobatiformes order, derived from rays, is characterized by viviparity and distinctive serrated stings, with some species exhibiting hexagonal dental plates. These marine organisms inhabit coastal zones globally. This study aims to enhance understanding of Quaternary biodiversity and paleoecology in southern Brazil, focusing on fossils from the Myliobatiformes order, specifically dental plates and stings. Material from biodetrital deposits at Concheiros and Hermenegildo beaches in Santa Vitória do Palmar, Rio Grande do Sul, Brazil, were analyzed. Six taxa were identified from fossil teeth, including Myliobatis ridens, Myliobatis freminvillei, Myliobatis goodei, and Myliobatis sp. (Morphotypes 1 and 2), marking their first Pleistocene fossil record in Brazil. Most teeth couldn't be classified at the species level, but genera were discerned. Fossil stings were described, possibly associated with Myliobatiformes. Results revealed notable differences between identified fossil taxa and their modern counterparts in the western Atlantic Ocean, currently considered common. M. ridens was the most frequent species in the fossil samples, followed by M. freminvillei, with fewer records for M. goodei. Conversely, the current scenario shows M. goodei as the most abundant, followed by M. freminvillei, while M. ridens is Critically Endangered. This investigation expands knowledge of fossil species on the southern Brazilian coast, confirming the presence of M. ridens, M. freminvillei, and M. goodei during the Quaternary.

Taxonomic and functional diversity of zooxanthellate corals and hydrocorals in Southwestern Atlantic reefs

The Southwestern Atlantic (SWA) harbors a relatively species poor but highly endemic coral assemblage due to historical processes, environmental and ecological drivers. Despite its low to moderate cover, corals still have a disproportionate contribution to ecosystem function and stability in this region. In the context of global change, it is imperative to know corals’ diversity and biogeographic patterns, yet a comprehensive approach is still missing for SWA corals. We integrated occurrence data from 21 sites and nine functional traits across 20 coral (scleractinian and hydrozoan) species to explore the taxonomic and functional diversity of coral assemblages in the SWA (1°N-27°S). We identified eight regions based on coral species composition, and then described their functional diversity using four metrics: functional richness (FRic), functional dispersion (FDis), functional evenness (FEve), and functional originality (FOri). Taxonomic and functional diversity peak between latitudes 13°S-20°S, decreasing with increasing distance from this diversity center, known as the Abrolhos Bank that harbors a wide continental platform. Our findings reveal a prevalent pattern of high functional redundancy across these eight regions (indicated by low functional originality), with species occupying the edges of the trait space (high functional evenness) and converging around few trait values (low functional dispersion). Such patterns resulted in low taxonomic and functional beta diversity and increased nestedness among regions caused by dispersal barriers and environmental filtering. The Southernmost region (24°-27°S) has the lowest taxonomic and functional diversity and comprises only two species that share similar traits, with these corals being: hermaphrodites, brooders and depth-tolerant, and having a wide corallite. As this region might become critical for corals in a future tropicalization scenario, tropical corals that share similar traits to those of the southernmost region can be more likely to thrive. Knowledge on taxonomic and functional diversity patterns can offer critical information to conservation by helping prioritizing areas with higher diversity and species with traits that enhance survival under climate change.

Vertical structure of reef fish assemblages and light penetration reveal new boundaries of mesophotic ecosystems in the subtropical Southwestern Atlantic

In the Southwest Atlantic, fisheries and in situ observations suggest that mesophotic reefs occur further south than has been reported in the literature, and a description of these subtropical regions is still lacking. We used Baited Remote Underwater stereo-Videos to explore unrevealed patterns in the vertical structure of fish assemblages on subtropical Atlantic reefs, contrasting shallow and mesophotic habitats. Our data on species turnover and light penetration reveal that in the subtropical Atlantic, the boundaries between shallow and mesophotic habitats occur at depths of 18 m, which is shallower than most previous studies have shown. Generalized additive mixed models identified different environmental and management factors as important predictor variables that explain distribution of fish assemblages’ attributes. Besides adding new evidence about mesophotic limits, we described variations in the vertical structure of fish assemblages, providing important information for the description and conservation of mesophotic environments in subtropical regions.

Associated fauna in a mesophotic rhodolith bed in the Campos Basin, Brazil, southwestern Atlantic

Rhodolith beds are predominantly formed by calcareous red algae with a rich benthic fauna. Nonetheless, little is known about the biota relationships with their structural variability. Rhodolith shape, size and vitality were examined from 22 sampling stations in dense and sparse areas of a mesophotic rhodolith bed in the Campos Basin, Brazil located within a major oil production area. Nine taxonomic benthic faunal groups were identified: Mollusca (58 taxa), Polychaeta (51), Echinodermata (27), Crustacea (24), Bryozoa (20), Porifera (19), Cnidaria (6), Ascidiacea (2) and Brachiopoda (1). Cnidaria, Mollusca, Bryozoa and Brachiopoda were abundant in areas with gravelly/rhodolith bottoms, while Polychaeta were associated with sandy/muddy bottoms. The faunal composition in the Peregrino oil field showed greater species richness than observed in other rhodolith beds worldwide. The present study contributes to the knowledge of the structural, taxonomical and functional characteristics of a rhodolith bed present along the Brazilian continental shelf.

Predation effects on benthic communities are maximized by greater taxonomic richness and diversity in Subtropical SW Atlantic

Predation effects on benthic communities are locally influenced by biological and ecological processes, such as recruitment, competition, and habitat features. We studied three Southwestern Atlantic (SWA) subtropical reef habitats (a rhodolith bed, a coral reef, and a rocky shore) to test if the predation effects on benthic communities overwhelm the habitat-context differences. We deployed panels protected and unprotected from predators on the three habitats, retrieved the panels after 45 days and quantified the recruitment of benthic sessile organisms. Despite differences in the composition of benthic assemblages, the effect of predation was mainly driven by the reduction of the ubiquitous polychaeta Spirorbidae in the three habitats. For the rhodolith bed, which supported a higher taxonomic richness and diversity than the other habitats, predation effects were higher and also driven by the reduction of other taxa. Although we recorded a greater predation effect in more diverse reefs, we attribute this result to small scale traits intrinsic to each habitat instead large-scale oceanographic patterns. Our results add pieces into the debate about how predation affects marine habitats and the importance of small-scale understanding for direct management actions in marine conservation.

Sponge Communities of Submarine Caves and Tunnels on the Fernando de Noronha Archipelago, Northeast Brazil

Submarine caves are important biodiversity reservoirs, but there is little information about the biota of marine caves in the Southwestern Atlantic. Here, we describe three submarine cavities and their sponge communities on the Fernando de Noronha Archipelago, Northeast Brazil. The underwater cavities were explored and collections were made through scuba diving from 5 to 18 m depths. Sapata Cave has a wide semi-dark zone near the entrance, a narrow transition zone, and a dark chimney, which is closed at the top. Ilha do Meio Cave is narrower and shallower than Sapata Cave, but has a long passage that leads to two completely dark rooms. Pedras Secas Tunnel has only a semi-dark zone with high water movement. The sponge communities in the semi-dark zones of the three cavities are rich and dominated by the classes Demospongiae and Homoscleromorpha, but Calcarea are also common. The transition zones of both caves are dominated by a desma-bearing sponge, thinly encrusting spirastrellids, and small Homoscleromopha and Calcarea. The dark zone in Ilha do Meio Cave is almost azoic, with only three species. This study has increased the number of sponge species known in submarine cavities on Fernando de Noronha from 29 to 69, highlighting the great richness of the sponge communities in these cryptic environments.

The Rio Grande Rise circulation: Dynamics of an internal tide conversion hotspot in the Southwestern Atlantic

The Rio Grande Rise (RGR) is a plateau located at 31°S in the Southwestern Atlantic, rising from 5916m up to 161m below the sea level. The RGR is an important site for future mining of Fe-Mn crusts and can lead to an expansion of Brazil’s Exclusive Economic Zone. The Cruzeiro do Sul Rift (CSR) fault cuts through the RGR from southeast to northwest. In this study we characterize the RGR circulation, showing that M2 tides are the main source of variability in the region, with an amplitude that can reach 0.3ms−1, larger than the mean flow. These M2 tides are dominated by the baroclinic component and intensified near the bottom. The generation of M2 internal tides occurs mainly in the CSR slopes, with most energy converted from the barotropic tide being radiated away in the form of tidal beams. In addition, the impingement of the mean southern South Equatorial Current and tidal rectification generates anticyclonic circulations around the RGR peaks, with the latter mechanism being responsible for a bottom intensified anticyclonic circulation of 0.2ms−1. Finally, our results reveal that the RGR is a hotspot of internal tide generation in the Southwestern Atlantic.