Ocean acidification is a major threat to coral reefs worldwide, with reduced growth already reported in the hydrocoral Millepora alcicornis (Linnaeus, 1758) under these conditions. Inhibition of enzymes related to energy metabolism is hypothesized as one of the mechanisms associated with the physiological impacts of ocean acidification. Therefore, a mesocosm experiment was conducted to investigate whether three levels of decreasing seawater pH could alter the activity of key enzymes involved in the energy metabolism in M. alcicornis. Hydrocorals were acclimated to marine mesocosm conditions for 20 days and then exposed to different seawater pH levels [ambient pH (8.1) and experimental pH (7.8, 7.5 and 7.2)] for 16 and 30 days. Endpoints analyzed included the activity of key enzymes involved in the regulation of the glycolytic pathway (hexokinase and pyruvate kinase), aerobic energy production via the Krebs cycle (citrate synthase) and anaerobic energy production via lactate formation (lactate dehydrogenase). The results obtained show that only citrate synthase was affected by seawater acidification, as a marked reduction in its activity was observed at all experimental pH levels tested (7.8, 7.5 and 7.2). This finding indicates that reduced growth previously reported for M. alcicornis under seawater acidification conditions can be explained, at least in part, by a negative impact on the Krebs cycle, a major pathway involved in aerobic energy production.

Anthropogenic climate change combined with the 2023–24 El Niño-Southern Oscillation triggered the fourth global bleaching event, affecting coral reefs worldwide. However, the extent of its impacts on the unique and extensive reef environments in the Southwestern Atlantic remained unquantified. Here, we report results from the first large-scale, standardized bleaching monitoring effort in the Southwestern Atlantic, encompassing 18 reef sites across a broad latitudinal range (3°-27°S). The intensity and duration of the thermal stress experienced were evaluated using the Degree Heating Week metric, obtained through remote-sensing data. Bleaching and coral cover loss were monitored through photoquadrat surveys conducted before, during, and after the event. Our results revealed widespread thermal anomalies that often exceeded 20 °C-weeks and lasted 3–5 months. Bleaching incidence reached 96

Southwestern Atlantic reefs are experiencing increased bleaching-associated mortality, prompting the proposal of active coral restoration as a solution. However, this approach faces challenges such as genetic bottlenecks, cost, scale, survival amidst local and global impacts, and long-term efficacy. Thus, we reviewed the major attributes of Southwestern Atlantic reefs and their coral species to assess the feasibility of active coral restoration in this unique biological and oceanographic setting. We also examined existing restoration techniques and their applicability to Southwestern Atlantic coral species and reef sites. Few species meet both suitability and priority criteria for restoration, with only Millepora alcicornis, Mi. braziliensis, and Mi. nitida, and, to a lesser extent, Mussismilia braziliensis emerging as relevant candidates. In this low-diversity region, suitable species are scarce, and identifying suitable restoration sites is challenging due to widespread local impacts and ineffective policy enforcement. We propose that practitioners (i) master species-specific fragmentation, handling, care, and monitoring techniques; (ii) align restoration practices with scientific knowledge; (iii) avoid combining multiple interventionist techniques; (iv) acknowledge potential conflicts of interest in restoration practices; and that (v) government agencies oversee restoration activities, and that transparency reports be generated. Southwestern Atlantic reefs need custom-designed conservation measures, and baseline data is essential for identifying suitable restoration sites. Although few species are viable candidates for restoration, and its effectiveness in restoring degraded reefs is unproven under current climate conditions, following the proposed ethical and ecological guidelines may help sustain threatened species and ecosystem services in degraded areas until climate change policies take effect.

The family Plexauridae Gray, 1859 is characterized by grouping octocorals that have thick branches and coenenchyme. However, due to their relatively simple body plan, the establishment of homologous and, therefore, systematically informative morphological characters is a challenge for the systematics of Octocorallia. During the last decade, molecular studies suggested that Plexauridae is polyphyletic, with representatives grouping with Acanthogorgiidae Gray, 1859 and also Gorgoniidae Lamouroux, 1812. Represented by 22 extant species, mostly of which occur in the Atlantic Ocean, the plexaurid genus Thesea Duchassaing Michelotti, 1860 has also been purported to be polyphyletic, with a Pacific lineage related to the former Paramuriceidae and an Atlantic lineage more closely related to Gorgoniidae. Thus, aiming to further improve our understanding of the evolutionary position of the Southwestern Atlantic Thesea, sequencing of the extended Octocorallia barcode reinforces the need for a re-evaluation of the position of the genus within plexaurids. Molecular and macro and micromorphological analyzes indicate the occurrence of an undescribed species distributed from Rio de Janeiro to Santa Catarina, here named Thesea pyrrha sp. nov. Results presented herein also suggest that T. pyrrha is close related to Adelogorgia and Psammogorgia, both genera exclusive to the Pacific Ocean.

The Southwestern Atlantic harbors unique reef environments with high proportions of endemic species. The most prominent reefs are located in the Abrolhos Bank, a 46,000 km2 extension of the South American continental shelf. However, just 100 km north of Abrolhos is the Royal Charlotte Bank (RCB), an area still poorly investigated. From a biological perspective, the only scientific information available is the historical record of lobster fisheries in the region. Hence, we performed an expedition to investigate what macrohabitats are found in the RCB and perform a preliminary biodiversity assessment. A dropcam was deployed in 67 sites and recorded images of macrohabitats and associated biodiversity. Four different macrohabitats were detected: rhodolith beds, macroalgal forests associated with rhodolith beds, calcareous sand deposits and coral reefs. The former two were the most frequent, and both rhodolith and macroalgae densities were higher on the outer shelf. A total of 83 species of fish, invertebrates and algae were identified, which comprises a comparatively high diversity for visual reef biodiversity assessments in the Southwestern Atlantic. Our findings show that the RCB is a large and diverse ecosystem complex mostly composed of rhodoliths, and also that it may be already undergoing anthropogenic impacts associated with climate change and fisheries. Therefore, further investigations are necessary to understand the extent of biodiversity and its main threats and evaluate the possible need of conservation and management measures.

Terrestrial runoff is a source of sediments and nutrients to coral reefs. Due to runoff, Brazilian reefs are typically turbid, and have coral species that are naturally turbidity-resistant.This study investigated how terrestrial input influences population and physiology for the coral Favia gravida on two reefs with differences in river mouth proximity in eastern Brazil. The population structure and physiological traits of F. gravida colonies were assessed on both reefs, then some colonies selected for a subsequent transplantation experiment. The reef less impacted by terrestrial influence showed higher population density and lower recruitment. At this site, the coral colonies displayed higher calcification and larger larvae. The reproductive effort between coral populations at the two sites showed no significant difference. The transplantation experiment confirmed the high physiological plasticity of F. gravida colonies at the more turbid reef site. Despite being regarded as a more challenging environment, where F. gravida has a lower population density, the reef closer to the river mouth appears to secure more nutrients, which may heterotrophically compensate its coral colonies.

Rivers release freshwater, nutrients and pollutants into reefs. This type of environmental stress reduces coral larvae settlement and alter its energy metabolism. We investigated the tolerance of Favia gravida (Scleractinia) larvae to river discharges. We exposed larvae to (i) different salinities (25, 30, 35 and 40 PSU); and (ii) dilutions of river water containing nutrients and metals (0, 20, 40, 60, 80 and 100% river water) under control salinity of 35 PSU. We then examined settlement and larval enzymatic activity. No differences in settlement were detected among salinities. Settlement was also similar to control for larvae under 100% river water. Enzymatic activity for citrate synthase remained unaltered for all treatments. Lactate dehydrogenase activity was slightly altered under different salinities, suggesting a mild stress response. Findings suggest that F. gravida larvae are tolerant to a wide range of salinity and nutrient conditions and that this is a stress-tolerant species.

The third global-scale coral bleaching event, triggered by the 2015-2016 El Nino, presented unprecedented levels of thermal stress and bleaching occurrence. Identification of potential cellular biomarkers in key reef species can greatly improve coral reef resource manager's ability to make ecological forecasts and develop efficient mitigation strategies. In this context, the present study evaluated ecologically relevant biochemical parameters involved in thermal-stress response in two important reef building species of southwestern Atlantic Reefs - the scleractinian coral Mussismilia harttii and the hydrocoral Millepora alcicornis - aiming to assess their potential to forecast bleaching occurrence in corals/hydrocorals. Bleaching frequency, lipid peroxidation (LPO) and total antioxidant capacity (TAC), as well as thermal stress parameters (Degree Heating Weeks, DHW), were monitored during a six-month period in a reef area under influence of the 2015-2016 El Nino event. LPO is suggested as an informative, cost-effective and logical complement to reef monitoring programs; and TAC basal level as a potential measurement for predicting corals/hydrocorals susceptibility to bleaching. Further, results indicate M. alcicornis as a promising bioindicator in South Atlantic reefs. Findings presented here are expected to improve South Atlantic coral reef monitoring programs, as well as to contribute with potential biomarker-monitoring techniques to be used as additional tools in traditional reef monitoring programs worldwide. Further, observations on oxidative stress responses of a hydrocoral undergoing thermal stress conditions in the field are reported here for the first time.

Aim Our aim was to uncover patterns of distribution of marine subtidal rocky reef communities across six taxonomic groups and decompose the relative roles of species loss and turnover in total community variation. Additionally, we propose an easily calculated index that can be used to highlight areas with unique species composition for conservation planning. We estimated the strengths of associations between environmental factors and species richness and rarity. Location Ilha Grande Bay, Brazil, covering about 150,000 ha harbouring different marine habitats. Methods We used the Marine Rapid Assessment Protocol at 42 sites to gather information on environmental variables and species in six subtidal marine groups. We determined "singular" sites as the regions harbouring higher numbers of rare species. Then, we estimated the roles of species loss and turnover on the observed total variation among sites. We used Generalized Linear Model to partition the relative importance of the selected environmental factors in driving variation in species richness and singularity. Results The singularity index and richness showed that the bay could be divided into three subregions for subtidal communities. Richness and rarity were structured at different spatial scales and associated with environmental variables related to water productivity and nutrients but varied among taxonomic groups. Community variation over space was largely associated with turnover of species. Main conclusions Higher singularity and richness on the western side of the bay and around the main island suggested that these regions should be conservation priorities, but high species turnover across the whole bay indicated that portions of the central channel should be included in conservation strategies. This draws attention to the importance of community variation rather than just species numbers in conservation and management planning. The high species turnover indicated that these rocky reefs have high beta diversity when compared to other studied biological systems.

Coastal areas face high variability of seawater pH. Ocean acidification (OA) and local stressors are enhancing this variability, which poses a threat to marine life. However, these organisms present potential phenotypic plasticity that can offer physiological and structural tools to survive in these extreme conditions. In this study, we evaluated the effects of elevated CO2 levels and consequent pH reduction on the physiology, anatomy and ultrastructure of the seagrass Halodule wrightii. A mesocosm study was conducted in an open system during a 30-day experiment, where different concentrations of CO2 were simulated following the natural variability observed in coastal reef systems. This resulted in four experimental conditions simulating the (i) environmental pH (control condition, without CO2 addition) and (ii) reduced pH by − 0.3 units, (iii) − 0.6 units and (iv) − 0.9 units, in relation to the field condition. The evaluated population only suffered reduced optimum quantum yield (Y(II)), leaf width and cross-section area under the lowest CO2 addition (− 0.3 pH units) after 30 days of experiment. This fitness commitment should be related to carbon concentration mechanisms present in the evaluated species. For the highest CO2 level, H. wrightii demonstrated a capacity to compensate any negative effect of the lowest pH. Our results suggest that the physiological behaviour of this primary producer is driven by the interactions among OA and environmental factors, like irradiance and nutrient availability. The observed behaviour highlights that high-frequency pH variability and multifactorial approaches should be applied, and when investigating the impact of OA, factors like irradiance, nutrient availability and temperature must be considered as well.

Acclimatization via changes in the stable (core) or the variable microbial diversity and/or abundance is an important element in the adaptation of coral species to environmental changes. Here, we explored the spatial-temporal dynamics, diversity and interactions of variable and core bacterial populations associated with the coral Mussismilia hispida and the surrounding water. This survey was performed on five reefs along a transect from the coast (Reef 1) to offshore (Reef 5), representing a gradient of influence of the river mouth, for almost 12 months (4 sampling times), in the dry and rainy seasons. A clear increasing gradient of organic-pollution proxies (nitrogen content and fecal coliforms) was observed from Reef 1 to Reef 5, during both seasons, and was highest at the Buranhém River mouth (Reef 1). Conversely, a clear inverse gradient of the network analysis of the whole bacterial communities also revealed more-complex network relationships at Reef 5. Our data also indicated a higher relative abundance of members of the bacterial core, dominated by Acinetobacter sp., at Reef 5, and higher diversity of site-stable bacterial populations, likely related to the higher abundance of total coliforms and N content (proxies of sewage or organic pollution) at Reef 1, during the rainy season. Thus, the less “polluted” areas may show a more-complex network and a high relative abundance of members of the bacterial core (almost 97% in some cases), resulting in a more-homogeneous and well-established bacteriome among sites/samples, when the influence of the river is stronger (rainy seasons).

Climate change, pollution and increased runoff are some of the main drivers of coral reefs degradation worldwide. However, the occurrence of runoff and marine pollution, as well as its ecological effects in South Atlantic coral reefs are still poorly understood. The aim of the present work is to characterize the terrigenous influence and contamination impact on the environmental health of five reefs located along a gradient of distance from a river source, using geochemical, water quality, and ecological indicators. Stable isotopes and sterols were used as geochemical indicators of sewage and terrigenous organic matter. Dissolved metal concentrations (Cu, Zn, Cd, and Pb) were used as indicators of water quality. Population density, bleaching and chlorophyll α content of the symbiont-bearing foraminifer Amphistegina gibbosa, were used as indicators of ecological effects. Sampling was performed four times during the year to assess temporal variability. Sediment and water quality indicators showed that reefs close to the river discharge experience nutrient enrichment and sewage contamination, and metals concentrations above international environmental quality guidelines. Higher levels of contamination were strongly related to the higher frequency of bleaching and lower density in A. gibbosa populations. The integrated evaluation of stable isotopes, sterols and metals provided a consistent diagnostic about sewage influence on the studied reefs. Additionally, the observed bioindicator responses evidenced relevant ecological effects. The water quality, geochemical and ecological indicators employed in the present study were effective as biomonitoring tools to be applied in reefs worldwide.

Global impacts are affecting negatively coral reefs’ health worldwide. Ocean acidification associated with the increasing CO 2 partial pressure in the atmosphere can potentially induce oxidative stress with consequent cellular damage in corals and hydrocorals. In the present study, parameters related to oxidative status were evaluated in the hydrocoral Millepora alcicornis exposed to three different levels of seawater acidification using a mesocosm system. CO 2 -driven acidification of seawater was performed until reaching 0.3, 0.6 and 0.9 pH units below the current pH of seawater pumped from the coral reef adjacent to the mesocosm. Therefore, treatments corresponded to control (pH 8.1), mild (pH 7.8), intermediate (pH 7.5) and severe (pH 7.2) seawater acidification. After 0, 16 and 30 d of exposure, hydrocorals were collected and the following parameters were analyzed in the holobiont: antioxidant capacity against peroxyl radicals (ACAP), total glutathione (GSHt) concentration, reduced (GSH) and oxidized (GSSG) glutathione ratio (GSH/GSSG), lipid peroxidation (LPO) and protein carbonyl group (PC) levels. ACAP was increased in hydrocorals after 16 d of exposure to intermediate levels of seawater acidification. GSHt and GSH/GSSG did not change over the experimental period. LPO was increased at any level of seawater acidification, while PC content was increased in hydrocorals exposed to intermediate and severe seawater acidification for 30 d. These findings indicate that the antioxidant defense system of M. alcicornis is capable of coping with acidic conditions for a short period of time (16 d). Additionally, they clearly show that a long-term (30 d) exposure to seawater acidification induces oxidative stress with consequent oxidative damage to lipids and proteins, which could compromise hydrocoral health.

Understanding connectivity patterns has implications for evolutionary and ecological processes, as well as for proper conservation strategies. This study examined population genetic structure and migration patterns of the coral Mussismilia hispida , one of the main reef builders in the Southwestern Atlantic Ocean. For this, 15 sites were sampled along its entire distributional range employing 10 microsatellite loci . M . hispida was divided into five genetically differentiated populations by Structure analysis. Population structure and migration estimates are consistent with present-day oceanographic current patterns, zones of upwelling and historical sea-level changes. The Central Region and Oceanic Islands populations had the highest genetic diversity, were possibly the main sources of migrants for other populations and presented mutual migrant exchange. This mutual exchange and the high diversity of Oceanic Islands, a peripherical population, is highly interesting and unexpected, but can be explained if these sites acted as refugia in past low sea-level stance. This is the first connectivity study in the region using hyper-variable markers and a fine sampling scale along 3,500 km. These results enlighten the population dynamics of an important reef building species and shows how oceanographic processes may act as barriers to dispersal for marine species, providing valuable information for management strategies.

Symbiodinium are responsible for the majority of primary production in coral reefs and found in a mutualistic symbiosis with multiple animal phyla. However, little is known about the molecular signals involved in the establishment of this symbiosis and whether it initiates during host larval development. To address this question, we monitored the expression of a putative symbiosis-specific gene (H+-ATPase) in Symbiodinium A1 ex hospite and in association with larvae of a scleractinian coral (Mussismilia hispida), a nudibranch (Berghia stephanieae) and a giant clam (Tridacna crocea). We acquired broodstock for each host, induced spawning and cultured the larvae. Symbiodinium cells were offered and larval samples taken for each host during the first 72 h after symbiont addition. In addition, control samples including free-living Symbiodinium and broodstock tissue containing symbionts for each host were collected. RNA extraction and RT-PCR were performed and amplified products cloned and sequenced. Our results show that H+-ATPase was expressed in Symbiodinium associated with coral and giant clam larvae, but not with nudibranch larvae, which digested the symbionts. Broodstock tissue for coral and giant clam also expressed H+-ATPase, but not the nudibranch tissue sample. Our results of the expression of H+-ATPase as a marker gene suggest that symbiosis between Symbiodinium and M. hispida and T. crocea is established during host larval development. Conversely, in the case of B. stephanieae larvae, evidence does not support a mutualistic relationship. Our study supports the utilization of H+-ATPase expression as a marker for assessing Symbiodinium–invertebrate relationships with applications for the differentiation of symbiotic and non-symbiotic associations. At the same time, insights from a single marker gene approach are limited and future studies should direct the identification of additional symbiosis-specific genes, ideally from both symbiont and host.

Ocean acidification is expected to intensify due to increasing levels in the partial pressure of atmospheric CO2 (pCO2). This could negatively affect major calcifying reef organisms. In this study, the effects of different levels of CO2-driven acidification of seawater (control: pH 8.1; moderate: pH 7.8; intermediate: pH 7.5; and severe: pH 7.2) on the net calcification rate and activity of enzymes related to the calcification process (Ca-ATPase and carbonic anhydrase) were evaluated in the calcareous hydrozoan Millepora alcicornis. The experiment was run for 30 d using a marine mesocosm system. Net calcification ratio was significantly reduced in hydrocorals exposed to intermediate seawater acidification for 16 d and to severe seawater acidification for 16 d or 30 d, compared to animals at control conditions. However, only hydrocorals exposed to severe seawater acidification showed lower net calcification rates than those exposed to control conditions for 30 d. In accordance, the activities of enzymes involved in the calcification process markedly increased in hydrocorals exposed to reduced pH. Ca-ATPase seemed to be more sensitive to seawater acidification than carbonic anhydrase as it increased in hydrocorals exposed to intermediate and severe seawater acidification for 30 d, while carbonic anhydrase activity was only stimulated under severe seawater acidification. Therefore, our findings clearly show that the hydrocoral M. alcicornis is able to cope, to some extent, with long-term CO2-driven acidification of seawater (pH ≥ 7.5). In addition, they show that Ca-ATPase plays a key role in the maintenance of calcification rate under scenarios of moderate and intermediate levels of seawater acidification. However, the observed increase in Ca-ATPase and carbonic anhydrase activity was not enough to compensate for the effects of CO2-driven reduction in seawater pH on the net calcification rate of the hydrocoral M. alcicornis under a scenario of severe ocean acidification (pH 7.2).