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The continental margin off the southeastern Brazilian coast is punctuated by a series of geological-geomorphological features, such as subsurface saline diapirs and pockmarks at the seafloor interface, which evidence the abundant presence of oil and gas in the region. In several of these sites, hydrocarbons can be naturally released into the water column, areas are cold seep areas. These are marked by the presence of oil- and gas-dependent ecosystems, where specific organisms are able to fix carbon from hydrocarbon chemosynthesis. In addition, light hydrocarbon fluid flow through the sediment may build up authigenic carbonates that can be further colonized by cold-water corals, generating large carbonate mounds over geological time, normally positioned at the border of these pockmark features. The present work reports on a multidisciplinary oceanographic cruise carried out in the Santos Basin, SW Atlantic, to seek, map, and collect geological, chemical, and biological data from different deep-sea habitats. The cruise occurred in November 2019 on the R/V Alpha Crucis of the Oceanographic Institute of the University of São Paulo (IOUSP). We intended to discover and detail different geomorphological features, characterize free-living and symbiotic microorganisms, determine the chemosynthetic rates in relation to heterotrophic microbial production, and characterize the fauna and study their ecological and evolutionary links within and across ocean basins. All discoveries made during the cruise and their respective results will be presented separately in several papers that comprise this special volume.

South Atlantic deep waters provide a huge diversity of habitats, with variations in areas such as geology, macrofauna, microbiology, physics, and chemistry. However, most of the data lacks central organization, important for subsequent deep-sea research, especially considering the multidisciplinary approaches and comparisons of the South Atlantic with other oceanic basins. Given the rising interest in commercial exploration off the deep-sea, especially with respect to hydrocarbon extraction and mining, there is an urgent need for a centralized repository of information with tools to collect and share geospatial data to support the conservation of this important oceanographic region. The main objective of this manuscript is to present an integrative database in WebGIS format for South Atlantic deep waters, open to further development in terms of data input, reliant on researcher collaboration, and with tools for ongoing maintenance and usability improvement driven by user feedback. The WebGIS format provides an open access, cost-free, feature-rich, and easy to use database through any Internet browser to reach the greatest number of researchers and students possible. The ABYSSAL database can be accessed at http://abyssal.io.usp.br.

The SE Brazilian continental margin is rich in geomorphological features that create different seascapes, where diverse benthic communities thrive. The seafloor is composed of a mixture of pockmarks of different sizes and shapes and tall carbonate mounds that may form extensive chains. Mounds are colonized by deep-water corals which are the main responsible organisms promoting growth over geological time. Depressions and mounds affect the benthic ecosystem in multiple ways owing to water flow, sedimentation rates and food availability. This paper presents new data on macrofaunal composition and community structure associated with deep-sea coral habitats and pockmark areas along the upper continental slope of Santos Basin. Ten sites were sampled using a 0.25 m2 box corer on board R/V Alpha-Crucis, totaling 27 sediment samples. A total of 182 taxa were found, including new records for the Southwestern Atlantic, as well as several potential new species to science. In general, we observed an association of the macrobenthic fauna with the geomorphology of the area and the most important variables, mainly substrate composition and water flux. The abundance, taxonomic composition and also the feeding modes varied across the deep-water coral sites and pockmarks, reflecting in a mosaic of benthic habitats. As deep-sea corals and pockmarks are extremely sensitive to anthropogenic influence and natural shifts, in addition to the economic value associated to fisheries, this study provides baseline information on these special habitats in Santos Basin that can be used for future research, monitoring activities, and conservation strategies.

Coral reefs globally are threatened by climate change, but reef assemblages at high latitudes may serve as refugia. Marginal coral communities located in the subtropical Southwestern Atlantic are poorly studied, but were subject to an unprecedented heatwave and associated coral bleaching in 2019. Record values of 18.5 and 20.5 °C-weeks were registered for coastal and insular sites, which are the highest ever documented for a reef in the South Atlantic. As a consequence, approximately 80% and 20% of the population of the reef-building coral Mussismilia hispida (1116 colonies surveyed) underwent bleaching in coastal and insular sites, respectively. However, mortality (2%) was far lower than for episodes of similar magnitude in other regions, particularly in the Indo-Pacific. Therefore, the subtropical Southwestern Atlantic MCC displayed low mortality and remarkable tolerance when exposed to the most intense bleaching episode ever recorded for the region, reinforcing its potential as a refugium.

Marine ornamental aquaculture is a growing industry. Although most species are cultured for aesthetic purposes, there is increasing interest in organisms that provide functional services. Nudibranchs provide an example in which they act as biological controls by consuming aquaria pests. Berghia stephanieae is a commercially relevant nudibranch that feeds on Exaiptasia anemones, which overgrow sessile invertebrates. However, information pertaining to B. stephanieae feeding habits remains unaddressed. Therefore, this study investigated the following: (a) the effect of feeding frequency on fecundity, (b) optimum prey size, (c) the ability to feed on prey fragments, and (d) the influence of intraspecific competition. Distinct feeding frequencies were tested and embryos produced were quantified; growth of nudibranchs offered different anemone sizes was measured; whole and fragmented anemones were offered, with preference recorded; and growth and mortality of juvenile nudibranchs were recorded in the absence and presence of adult conspecifics. Results show that feeding daily produced the highest number of embryos. Juveniles fed on medium‐sized anemones showed the highest growth rate. Smaller juveniles were unable to feed on whole anemones and preferred fragmented anemones. Juvenile growth and survival decreased in the presence of adults. To maximize production, breeders must feed broodstock daily, provide medium‐sized anemones or fragments, and segregate juveniles from adults.

Cassiopea jellyfish have successfully invaded several marine ecosystems worldwide. We investigated if Cassiopea andromeda grows larger (umbrella size) and if their populations are more stable in shrimp farms than in mangroves in the Brazilian coast. Our results show that jellyfish abundance is higher in the shrimp farm during the rainy season and in the mangrove during dry season. The population is stable during both seasons in the shrimp farm, but unstable in the mangroves, as jellyfish are absent during rainy season. Shrimp farm-associated jellyfish are three times larger than those in the mangroves, regardless of season. We recorded the largest (49.2 cm of umbrella diameter) ever C. andromeda individual in the shrimp farm. Unlike the mangroves, the shrimp farm provides environmental intra-annual stability that promotes jellyfish growth and population persistence. Therefore, C. andromeda populations can be seasonally dynamic and artificial environments such as aquaculture facilities may facilitate the invasion process.

Many species of reef-building corals are mixotrophic, relying on both photoautotrophy performed by their dinoflagellate symbionts and heterotrophy from consumption of zooplankton. Autotrophy and heterotrophy supply corals with specific ω3 fatty acids, which can be used as trophic markers and record the contribution of each feeding strategy. This study investigated whether the reef-building coral Mussismilia hispida, endemic to Brazil, is able to shift between predominantly autotrophic and predominantly heterotrophic by monitoring the concentration of fatty acids in the host tissue. We then examined whether shifts are related to changes in temperature and wind stress. For that purpose, M. hispida colonies were monitored for a year with monthly tissue sampling. Symbiont concentration was determined and lipid extraction performed. Four fatty acids were quantitatively analyzed by gas chromatography with flame ionization detector: the autotrophy markers: stearidonic acid (SDA), docosapentaenoic acid (DPA), docosahexaenoic acid (DHA), and a heterotrophy marker: cis-gondoic acid (CGA). Three preliminary experiments confirmed the specificity of SDA, DPA and CGA, but not of DHA. Shifts of predominance occurred multiple times during the year and were associated with minimal temperatures and wind stress. Colonies underwent mild bleaching during summer months, which they seemed to compensate with heterotrophic feeding. Our major findings include the validation of three FATM and a trophic index for coral reef ecology studies and also describing the in situ occurrences of shifts between feeding modes, while highlighting the role of temperature and meteorological events.

Despite the importance of jellyfish in marine ecosystems, many basic biological and ecological aspects remain understudied, especially in tropical regions. Here, we report on scyphozoan jellyfish distribution and ecology to the Amazon coast for the first time, adding the records of Chrysaora lactea, Lychnorhiza lucerna and Stomolophus fritillarius. We also review the records for the three species for the whole Brazilian coastline, describe temporal variability within an Amazon estuary and length–weight relationships. The three species displayed a widespread distribution on the Brazilian coast. In the studied estuary, the species are unevenly distributed throughout the year and their presence was not clearly correlated with environmental factors examined, although L. lucerna is more common during the dry season, as indicated by multivariate and correlation analysis. The length–weight relationships were significant for both L. lucerna (R2 = 0.86, P

Oceans are undergoing successive heatwaves. Several invertebrate taxa associate with dinoflagellates and are susceptible to bleaching caused by heat stress. Although the impacts of a single bleaching event have been well documented, the consequences of successive events are less understood. We investigated the effects of multiple thermal stress events on juvenile Cassiopea andromeda, while also addressing the roles of symbiont concentration and heterotrophic diet regimen. We exposed medusae with two distinct symbiont concentrations (high and low) and under two feeding frequencies (Artemia offered daily and every 3 days) to three thermal stress events and at three temperatures (control of 27 °C, and treatments of 30 and 33 °C) while recording proportional changes in chlorophyll-a and jellyfish growth. Results show that 30 and 33 °C were not enough to trigger bleaching and did not affect growth. Symbiont concentration also did not affect growth, but medusae with higher symbiont concentration displayed higher chlorophyll-a loss. Diet regimen had little impact on chlorophyll-a variation, but had a dramatic effect on growth, as medusae fed daily grew, while those fed every 3 days shrank. These findings show that it is not possible to evaluate if C. andromeda becomes more resilient after successive thermal stress episodes, because even 33 °C did not generate enough stress. Therefore, C. andromeda juveniles are thermotolerant and may not serve as a good model for investigations on the resilience of coral reef zooxanthellate fauna to the current climate change predictions. Finally, at this life stage, the symbiotic relationship seems less important for growth than heterotrophy.

Ocean warming is one of the greatest global threats to coral reef ecosystems, it leads to the disruption of the coral&ndash, dinoflagellate symbiosis (bleaching) and to nutrient starvation, because corals mostly rely on autotrophy (i.e., the supply of photosynthates from the dinoflagellate symbionts) for their energy requirements. Although coral bleaching has been well studied, the early warning signs of bleaching, as well as the capacity of corals to shift from autotrophy to heterotrophy, are still under investigation. In this study, we evaluated the bleaching occurrence of the scleractinian coral Mussismillia harttii and the hydrocoral Millepora alcicornis during a natural thermal stress event, under the 2015&ndash, 2016 El Ni&ntilde, o influence in three reef sites of the South Atlantic. We focused on the link between peroxynitrite (ONOO&minus, ) generation and coral bleaching, as ONOO&minus, has been very poorly investigated in corals and never during a natural bleaching event. We also investigated the natural trophic plasticity of the two corals through the use of new lipid biomarkers. The results obtained first demonstrate that ONOO&minus, is linked to the onset and intensity of bleaching in both scleractinian corals and hydrocorals. Indeed, ONOO&minus, concentrations were correlated with bleaching intensity, with the highest levels preceding the highest bleaching intensity. The time lag between bleaching and ONOO&minus, peak was, however, species-specific. In addition, we observed that elevated temperatures forced heterotrophy in scleractinian corals, as Mu. harttii presented high heterotrophic activity 15 to 30 days prior bleaching occurrence. On the contrary, a lower heterotrophic activity was monitored for the hydrocoral Mi. alicornis, which also experienced higher bleaching levels compared to Mu. hartii. Overall, we showed that the levels of ONOO&minus, in coral tissue, combined to the heterotrophic capacity, are two good proxies explaining the intensity of coral bleaching.

The symbiotic association with Symbiodiniaceae dinoflagellates has been more investigated for reef-building corals than for other metazoan taxa. Nudibranchs are relevant hosts as they present a wide variety of relationships with Symbiodiniaceae that range from predation to mutualistic association. The aeolid Berghia stephanieae is perhaps the best model for ecological studies in the mollusk-dinoflagellate association due to its hardiness, short life cycle and simple aquaculture protocols. However, it remains untested if B. stephanieae and Symbiodiniaceae actually engage in mutualism. Therefore, this study experimentally investigated the following aspects pertaining to the relationship between the two organisms: (i) Symbiodiniaceae retention time in the host tissue, (ii) effect of Symbodiniaceae presence in the prey item on host growth, and (iii) host capability to obtain free-living Symbiodiniaceae. Three experiments were performed: (i) monitoring of Symbiodiniaceae concentration in the cerata of starved B. stephanieae, (ii) offer of different-sized prey with and without symbionts and measuring B. stephanieae growth, and (iii) offer of free-living Symbiodiniaceae to B. stephanieae. Results show that the retention time (3–5 days) is much shorter than for many symbiont-associated nudibranchs. Berghia stephanieae growth is influenced by prey size, and apparently not affected by symbiont presence. Finally, this species is unable to obtain free-living Symbiodiniaceae. These results indicate that B. stephanieae does not meet criteria for a mutualistic relationship with Symbiodiniaceae, such as long-term retention and metabolite or favor exchange. This relationship may be in an evolutionary transitional stage, unlike the fully functional mutualism found in other organisms such as reef-building corals.