Benthic reef assemblages of the Fernando de Noronha Archipelago, tropical South-west Atlantic: Effects of depth, wave exposure and cross-shelf positioning

Interannual health status stability of the reef-building coral Montastraea cavernosa in a Southwestern Atlantic marginal reef

Severe coral mortality after bleaching is well documented in the Indo-Pacific and Caribbean, but in the marginal Southwestern Atlantic, corals often exhibit lower post-bleaching mortality and high recovery following temperature anomalies. Understanding how these corals respond to environmental fluctuations can provide insights into their resilience against thermal stress. A seven-year assessment of the dominant reef-building coral Montastraea cavernosa was conducted in the oceanic archipelago of Fernando de Noronha, Southwestern Atlantic (3.86°S 32°42W), using a colony-based approach. We quantified healthy and bleached coral areas, colony area covered by algae, colony's border interactions with benthic organisms, and adjacent benthic cover during austral spring and relate eventual patterns with environmental drivers. Between 2013 and 2019, analyses of 43 colonies across three sites (totaling 167 observations) revealed that they largely remained healthy, with over 70 % of the area exhibiting a vivid dark color, and only small bleached areas (less than 1 %), despite a moderate-strong heatwave in 2018-2019. The adjacent algal cover fluctuated and was positively related to more turbid waters (higher sedimentation and organic matter input), but the monitored colonies were more contacted than expected by chance by algal turfs, a benthic group that does not impose a major competitive threat to corals. While it is unclear if corals bleached between sampling periods, the results suggest that reefs dominated by M. cavernosa may resist/recover thermal stress events, differing from the responses observed in the Indo-Pacific and Caribbean, highlighting the importance of including these marginal reefs in global assessments of coral responses to climate change.

Pollution affects even oceanic marine protected areas in Southwestern Atlantic

Reefs are facing a global decline with sewage pollution emerging as a significant and poorly understood threat. Inadequate wastewater management and disorderly urbanization contribute to water pollution globally. Tropical Southwestern Atlantic comprises a set of oceanic Marine Protected Areas (MPAs) including the Fernando de Noronha Archipelago in Brazil, which has experienced significant population growth without expanding the sewage infrastructure. We mapped and quantified marine pollution in these MPAs, characterizing pollution sources and evaluating their effects on benthic and fish communities in 13 reef sites. We quantified nutrients, metals and metalloid, microplastics, fecal sterols, and Polycyclic Aromatic Hydrocarbons (PAHs) in both water and sediment samples. We also used isotopic tracing on macroalgae to identify the origin of organic matter and characterized benthic and fish communities, and algae biomass at each site. Pollution was more pronounced in the multiple-use area but also affected no-take areas. Effluents from wastewater treatment plants did not meet legislative standards, and reefs in the multiple-use area were enriched in orthophosphate and ammonia compared to those in the no-take area. Nitrogen isotopes in macroalgae revealed sewage-derived nitrogen throughout the multiple-use area. Nutrient enriched sites exhibited higher abundances of fast-growing and opportunistic green macroalgae, and higher biomass of brown macroalgae. The port area, within the multiple-use area, showed high PAHs, coprostanol and metal(loid) concentrations, suggesting untreated sewage and nautical chemical pollution. Microplastics were widespread in sediment and water samples. We documented the pervasive impacts of marine pollution on reef habitats even within marine protected areas in oceanic regions, demonstrating that local pollution control, sewage management and regulating procedures in port areas are critical to protect marine ecosystems. Comparisons with previous studies suggest marine pollution has substantially increased in the Archipelago in the last ten years. This is the first comprehensive assessment of marine pollution in an oceanic environment in Southwestern Atlantic, showing these isolated environments are not immune to pollution impacts.

Proxies to detect hotspots of invertebrate biodiversity on rhodolith beds across the Southwestern Atlantic

Rhodolith beds are known worldwide to host high biodiversity to several taxa. Despite their importance, few ecological data explored the influence of rhodolith features and environmental variables on associated biodiversity, a gap that has been hampering the mapping of diversity hotspots and priority areas for conservation. In this study, we investigated large-scale spatial variations of rhodolith beds and their associated fauna, using annelid polychaetes as a biological model. We aimed to identify proxies, based on rhodolith features and environmental variables, to detect biodiversity hotspots across Southwestern Atlantic beds, laying the groundwork for mapping priority areas for conservation. With this goal, we sampled a total of 136 rhodolith nodules across seven sites with beds under distinct latitudes, depths, distances from the mainland coast of Brazil, and rhodolith densities. For each nodule sampled, we measured the volume, diameter, and mass of sediment trapped, as well as the attributes of the associated polychaetes (abundance, richness, diversity, and composition). Our results revealed a complex network of collinearities and synergisms between the rhodolith features and the majority of the polychaetes attributes (i.e., abundance, diversity, and composition). Polychaete richness, in contrast, can be explained by the combination of two proxies: (1) rhodolith nodule diameter and (2) distance of the rhodolith bed from the mainland coast. Nearshore rhodolith beds and larger nodules were associated with higher values of richness. Additionally, rhodoliths with a hollow morphology were also associated with higher values of polychaete richness. These results suggest that nearshore rhodolith beds with large and hollow nodules could be priority areas for conservation. However, further multi-taxa studies using our framework are still needed to explore other regions and scales, delineating more comprehensive proxies for predicting ecological patterns of the rhodoliths associated fauna and to identify priorities for conservation across Southwestern Atlantic beds.

Modeling risks in marine protected areas: Mapping of habitats, biodiversity, and cultural ecosystem services in the southernmost atlantic coral reef

Marine Protected Area (MPA) is a fundamental strategy for the maintenance of ocean ecological processes worldwide and, consequently, their associated ecosystem services. Nevertheless, the quality of the services provided by MPAs, including cultural services such as recreational activities, depends on the effective management of marine habitats and biodiversity. Here, we performed an ecosystemic assessment in reef environments within a subtropical MPA, modeling the potential risks for their habitats and their recreational activities. The Queimada Grande Island (QGI), southeastern Brazil, was used as the model area since this island encompasses a unique and irreplaceable marine habitat, the Southernmost Atlantic coral reef. We firstly assessed and mapped the habitats, the biodiversity, and the recreational activities associated with QGI reefs. Next, we considered different scenarios of management for the modeling risks across the study area. We found that the coral reef and its adjacent habitats, such as the rhodolith bed, make the sheltered face of the island an important area for the provision of the cultural ecosystem services and overlapping uses such as onboard recreational fishing, spearfishing, and recreational diving. This area was also evaluated as the one under the highest risk of impact, considering the current scenario of management. The most successful scenario modeling to reduce these risks was the hypothetical implementation of a 66% reduction of all activities over all QGI habitats. Despite that, the scenario simulating the application of the regulations present in the MPA management plan was enough to reduce almost half the maximum risk value. Therefore, we concluded that to provide a balance among conservation, uses, and the local economy, the application of these regulations is the better management scenario modeled for the study area. Such results provided useful information and tools for local management and decision-making in this singular marine environment, also being an example for mapping ecosystem services and modeling risks in MPAs worldwide.

First acoustic evidence of signature whistle production by spinner dolphins (Stenella longirostris)

A dolphin's signature whistle (SW) is a distinctive acoustic signal, issued in a bout pattern of unique frequency modulation contours; it allows individuals belonging to a given group to recognize each other and, consequently, to maintain contact and cohesion. The current study is the first scientific evidence that spinner dolphins (Stenella longirostris) produce SWs. Acoustic data were recorded at a shallow rest bay called "Biboca", in Fernando de Noronha Archipelago, Brazil. In total, 1902 whistles were analyzed; 40% (753/1,902) of them were classified as stereotyped whistles (STW). Based on the SIGID method, 63% (472/753) of all STWs were identified as SWs; subsequently, they were categorized into one of 18 SW types. SWs accounted for 25% (472/1,902) of the acoustic repertoire. External observers have shown near perfect agreement to classify whistles into the adopted SW categorization. Most acoustic and temporal variables measured for SWs showed mean values similar to those recorded in other studies with spinner dolphins, whose authors did not differentiate SWs from non-SWs. Principal component analysis has explained 78% of total SW variance, and it emphasized the relevance of shape/contour and frequency variables to SW variance. This scientific discovery helps improving bioacoustics knowledge about the investigated species. Future studies to be conducted in Fernando de Noronha Archipelago should focus on continuous investigations about SW development and use by S. longirostris, expanding individuals' identifications (Photo ID and SW Noronha Catalog), assessing long-term whistle stability and emission rates, and making mother-offspring comparisons with sex-based differences.

Turbidity shapes shallow Southwestern Atlantic benthic reef communities

Southwestern Atlantic reefs (Brazilian Province) occur along a broad latitudinal range (∼5°N-27°S) and under varied environmental conditions. We combined large-scale benthic cover and environmental data into uni- and multivariate regression tree analyses to identify unique shallow (<30 m) benthic reef communities and their environmental drivers along the Brazilian Province. Turbidity was the leading environmental driver of benthic reef communities, with the occurrence of two main groups: clear-water (dominated by fleshy macroalgae) and turbid (dominated by turf algae). Seven out of 14 scleractinian coral species were more abundant in the turbid group, thus corroborating the photophobic nature of some Brazilian corals. The most abundant scleractinian in Brazil (Montastraea cavernosa), largely dominated (71-93% of total coral cover) both, the shallow turbid and deeper clear-water reefs. Because these habitat types are widely recognized as potential climate refuges, local threats (e.g. pollution, overfishing) should be averted.

Low functional vulnerability of fish assemblages to coral loss in Southwestern Atlantic marginal reefs

Marginal reefs sustain coral assemblages under conditions considered suboptimal for most corals, resulting in low coral abundance. These reefs are inhabited by numerous fishes with a generally unknown degree of association with corals that might lead to the assumption that corals play minor roles in determining fish occurrence, when corals could be actually sustaining diverse and resilient assemblages. Using site-occupancy models fitted to data of 113 reef fish species of different life stages (adults and juveniles) from 36 reefs distributed across the Southwestern Atlantic (0.87-27.6°S) we first assessed fish assemblage's response to coral and turf algal cover, and identified coral-associated fish. Then, we simulated the loss of coral-associated fishes and contrasted it with random losses, providing inferences on the resilience of fish assemblage's functional trait space to species loss. The entire fish assemblage responded more positively to coral than to turf algae, with 42 (37%) species being identified as coral-associated fish. The simulated loss of coral-associated fish reduced up to 5% the functional trait space and was not different from the random loss. These results reveal that marginal reefs of Southwestern Atlantic reefs host resilient fish assemblages that might preserve fundamental ecological functions and ecosystem services even with coral declines.

Ecosystem engineer morphological traits and taxon identity shape biodiversity across the euphotic-mesophotic transition

The euphotic-mesophotic transition is characterized by dramatic changes in environmental conditions, which can significantly alter the functioning of ecosystem engineers and the structure of their associated communities. However, the drivers of biodiversity change across the euphotic-mesophotic transition remain unclear. Here, we investigated the mechanisms affecting the biodiversity-supporting potential of free-living red coralline algae-globally important habitat creators-towards mesophotic depths. Across a 73 m depth gradient, we observed a general decline in macrofaunal biodiversity (fauna abundance, taxon richness and alpha diversity), but an increase in beta-diversity (i.e. variation between assemblages) at the deepest site (86 m depth, where light levels were less than 1% surface irradiance). We identified a gradient in abundance decline rather than distinct ecological shifts, driven by a complex interaction between declining light availability, declining size of the coralline algal host individuals and a changing host taxonomy. However, despite abundance declines, high between-assemblage variability at deeper depths allowed biodiversity-supporting potential to be maintained, highlighting their importance as coastal refugia.

Learning from differences: Abiotic determinism of benthic communities in Northern Taiwan

Differences in the initial configuration of ecological communities may lead to contrasting trajectories when facing environmental changes. Here, we propose to uncover the determinism of benthic communities by carrying out a detailed investigation of their response to small-scale modification of environmental conditions, including physical, chemical, and geological factors. At ten locations (confounding site and depth) in Northern Taiwan, communities were delineated using a morpho-functional classification of the organisms. A k-means clustering was used to identify k homogenous groups among transects. Their environmental determinism was examined by combining this result with 16 environmental variables of transect conditions into a regression tree framework. Biotic and abiotic data were further analyzed with a Multivariate Regression Tree (MRT) to ascertain the hierarchical environmental determinism. The classifications produced by both approaches were compared using the Adjusted Rand index (ARI) to assess the predictive power of unsupervised clustering on its missing explanatory components (abiotic variables). k-means and MRT produced five clusters, respectively, with a similarity of 0.82 in ARI. Wave motion, followed by substrate types resolved most of the variance, while chemical factors in this study were uniform throughout the region. Comparable structures for both methods (clustering groups) demonstrated that the delineated clusters matched with contrasting environmental conditions which could be explained by the existence of various benthic communities. Further consideration of these different communities and their environmental context will be important in determining their trajectories under global changes and may help in the interpretation of community modifications with changing environmental conditions.

Marine debris in the Fernando de Noronha Archipelago, a remote oceanic marine protected area in tropical SW Atlantic

Marine debris is widespread worldwide, from coastal areas to remote protected oceanic islands. We assessed marine macro-debris on the shores of Fernando de Noronha, an archipelago 360 km off Brazil that encompasses no-take and multiple-use areas. The windward uninhabited coast, more exposed to oceanic currents and winds and inside a no-take area, presented higher abundance of plastic debris. The leeward coast, within the multiple-use urban area, presented more disposable plastics and cigarette butts. These patterns may be explained by the marine debris transportation by ocean currents to the windward side and by locally generated debris by the high quantity of beach users in the leeward coast. These results indicate that oceanographic characteristics and tourism infrastructure play important roles in the accumulation of marine debris in a protected archipelago. They also serve as a baseline for future monitoring initiatives and to improve strategies to tackle plastic pollution within this remote archipelago.

Reef fishes biodiversity and conservation at the largest Brazilian coastal Marine Protected Area (MPA Costa dos Corais)

Abstract Coral reefs harbor one of the largest fish biodiversity on earth; yet information on reef fishes is still absent for many regions. We analyzed reef fish richness, distribution, and conservation on the largest Brazilian multiple use coastal MPA; which cover a large extent of coral reefs at the SWA. A total of 325 fish species have been listed for MPA Costa dos Corais, including Chondrichthyes (28 species) and Actinopterygii (297). Fish species were represented by 81 families and the most representative families were Carangidae (23 species), Labridae (21) and Gobiidae (15). The MPA fish richness represented 44% of all recorded fish species of the Southwestern Atlantic Ocean (SWA) highlighting the large-scale importance of this MPA. A total of 40 species (12%) are registered at Near Threatened (NT), Vulnerable (VU), Endangered (EN) or Critically Endangered (CR). This study reinforces the importance of MPA Costa dos Corais on reef fish biodiversity and conservation and emphasize the urgent need of conservation strategies.

Mesophotic ecosystems at Fernando de Noronha Archipelago, Brazil (South-western Atlantic), reveal unique ichthyofauna and need for conservation

Abstract Although several studies on the ichthyofauna of the Fernando de Noronha Archipelago have been carried out, its mesophotic fish diversity has never been surveyed before. Here we used SCUBA and technical rebreather diving, baited remote underwater videos and remotely operated vehicle to record shallow (≤ 30 m depth) and mesophotic (31 to 150 m depth) fishes. Nineteen fish species belonging to 14 families are reported here as new records, representing an increase of 8.2% in marine fish richness for the region, which now has a total of 250 species and 77 families. These new records include four potential new species and highlight the importance of surveying mesophotic ecosystems, even in well studied sites. Our results also emphasize the need for protection and attention to the unique ichthyofauna found at mesophotic depths.