Marine heatwaves (MHWs) and ocean acidity extremes (OAXs) are intensifying under anthropogenic climate change, and their compound co-occurrence can amplify ecological impacts. Yet the Agulhas Leakage, a key gateway transferring warm, saline Indian Ocean water into the Atlantic, remains understudied. Here we characterise MHWs over 1982–2024 and OAXs, and their compound events in this region over 1982–2021, comparing analyses of original and linearly detrended data. Under a fixed baseline, MHW cumulative intensity rose from approximately 29.95 to 109.51 °C-year in the original data and 49.4 to 66.7 °C-year after detrending between the first and fourth decades. OAX intensity increased from approximately 0.24 to 4.10 nmol kg–¹-year in the original data and from 0.35 to 0.46 nmol kg–¹-year after detrending. Compound events emerge only after the 2000s. Detrending reveals that most of this increase reflects the long-term warming and acidification trends, while residual variability remains in the dynamically active Agulhas Retroflexion, where anticyclonic eddies trap warm, high [H+] Indian Ocean waters. A likelihood multiplication factor confirms statistically significant positive MHW–OAX dependence that persists after detrending, indicating statistically significant positive co-occurrence between MHW and OAX on interannual timescales, consistent with physical coupling through carbonate chemistry. Baseline choice critically shapes compound-extreme risk assessment.
Continue reading ‘Extreme compound events in the Agulhas Leakage’Posts Tagged 'South Atlantic'
Extreme compound events in the Agulhas Leakage
Published 21 October 2026 Science Leave a CommentTags: chemistry, Indian, methods, South Atlantic
Assessing the projected impacts of climate change on underwater cultural heritage in the Nuevo Gulf, Argentina
Published 19 October 2026 Science Leave a CommentTags: chemistry, communityMF, modeling, multiple factors, oxygen, regionalmodeling, salinity, South Atlantic, temperature
Highlights
- CMIP6 models can quantify future climate threats to UHC sites in Northern Patagonia.
- Projected ∼2.1 °C warming by 2100 will accelerate corrosion and wood-boring activity.
- Ocean pH drop (4.5%) will accelerate corrosion and destabilise calcareous concretions.
- Salinity changes remain negligible across all projected climate change scenarios.
- UHC managers profit locally by integrating in situ data with climate model outputs.
Abstract
Climate change presents a significant and increasing threat to Underwater Cultural Heritage (UCH) worldwide. To better understand the risks that this entails, this study examines the archaeological wreck site of the schooner Emma in the Nuevo Gulf, Northern Patagonia, Argentina. It addresses a geographic research gap and the complex interaction of multiple environmental stressors. Using the information from state-of-the-art climate models, we assess the potential impacts in the near and far future of specific environmental parameters including temperature, salinity, dissolved oxygen, and pH, all relevant at the wreck site’s location, and identified to play a driving role in its conservation.
Results consistently demonstrate a clear trend toward a warmer and more acidic marine environment, with the greatest changes projected under the highest-emission scenario. In that case, sea temperature at the wreck site’s depth increases by approximately 14.5% (∼2.1 °C) by the end of this century, which would accelerate corrosion rates of metals and intensify the activity of wood-boring organisms. In parallel, acidification is projected to increase with pH decreasing by approximately 4.5% (∼0.36 units), contributing to the destabilisation of protective concretions and the intensification of metal corrosion. While dissolved oxygen is projected to decrease (∼3.92%) and salinity remains nearly unchanged, the synergy of warming and acidification suggests the wreck of the Emma will face a more aggressive environment by 2100. The methodology integrates a characterisation of the site’s materials, the main deterioration processes involved and the surrounding environmental context. This study also provides UCH managers with a climate-projection-based assessment of future slow-onset climate-related marine environmental pressures and the likely conservation implications that will inform the development of conservation and monitoring strategies for the Emma and other shipwrecks in the Nuevo Gulf and adjacent coastal areas.
Continue reading ‘Assessing the projected impacts of climate change on underwater cultural heritage in the Nuevo Gulf, Argentina’Developmental and behavioural responses of the non-indigenous amphipod Melita palmata (Montagu, 1804) at individual and population under reduced pH scenarios
Published 19 October 2026 Science Leave a CommentTags: biological response, crustaceans, laboratory, mortality, performance, reproduction, South Atlantic
Highlights
- Reduced pH disrupted early development, causing brood failure and incomplete eggs.
- Broods and cohorts showed high mortality, limited growth and irregular sex traits.
- Reduced pH altered behaviours, with sex-specific substrate use and slower escape.
- Multilevel responses suggest reduced pH may affect population stability and invasion.
Abstract
Non-indigenous species (NIS) and reduced pH conditions are key stressors shaping coastal biodiversity and population performance. We examined how decreased pH influences developmental, demographic, and behavioural traits of the non-indigenous amphipod Melita palmata from the Mar Chiquita coastal lagoon (Argentina). Individuals, broods, and cohorts were reared under current pH (8.07) and a reduced pH scenario (7.5) to assess egg maturation, brood and cohort survival, growth, sexual differentiation, habitat use, and escape responses. Reduced pH disrupted early developmental processes, leading to incomplete egg maturation, brood failure, and the absence of post-breeding moults. Broods and cohorts exhibited low survival, limited growth, and irregular sexual differentiation, and no ovigerous females were detected. Behavioural responses were also altered, with sex-specific shifts in substrate use and slower escape reactions. Together, these multilevel responses indicate that decreased pH induce physiological and behavioural constraints that propagate into demographic instability. Such response at both individual and population levels suggests that reduced pH conditions could limit the capacity of M. palmata to sustain populations and may influence its future invasion dynamics, although field-level consequences remain to be determined. These findings highlight how early acting individual responses can scale up to shape population persistence under projected coastal acidification scenarios.
Continue reading ‘Developmental and behavioural responses of the non-indigenous amphipod Melita palmata (Montagu, 1804) at individual and population under reduced pH scenarios’Long-term exposure to ocean acidification modifies the biochemical composition of the adductor muscle of the commercial scallop Zygochlamys patagonica
Published 7 October 2026 Science ClosedTags: biological response, fisheries, mitigation, mollusks, physiology, South Atlantic
The scallop Zygochlamys patagonica is an ecologically and economically important seafood species in the Southwest Atlantic Ocean that has been shown to be sensitive to ocean acidification (OA), a global process caused by anthropogenic carbon dioxide emissions. This study experimentally evaluated the effects of a long-term exposure to low pH, including an OA scenario on the scallop adductor muscle— the commercially valuable tissue. We tested three levels of pH, two pH values within the present range of natural variability (high pHT= 8.00 and medium pHT= 7.80) and a lower pH level representing a true OA scenario (low pHT: 7.52). We examined biochemical alterations induced by low pH and assessed the potential for reversibility following a depuration period. No significant effects were observed for medium pH exposure. However, after 14 and 28 weeks of exposure to low pH (OA), significant reductions in protein and total lipid content were observed, resulting in decreased overall energy reserves, while glycogen levels remained unchanged. The fatty acid profile shifted under OA with an increased PUFA/ SFA ratio and higher sums of EPA and DHA. No signs of recovery were detected after the 2-month depuration period. These results indicate that OA-driven changes in biochemical composition may reflect altered physiological status, with potential socio-ecological implications for the sustainable exploitation of this valuable resource.
Continue reading ‘Long-term exposure to ocean acidification modifies the biochemical composition of the adductor muscle of the commercial scallop Zygochlamys patagonica’Responses of reef fish populations to similar environmental changes across distant oceanic islands
Published 9 April 2026 Science ClosedTags: abundance, adaptation, biological response, chemistry, field, fish, otherprocess, South Atlantic
Oceanic islands are among the most remote and understudied regions of the planet, yet they harbour unique reef fish communities that are increasingly vulnerable to global environmental change. Because these islands are geographically isolated, their populations are often assumed to respond mainly to local environmental conditions. However, by analysing temporal patterns in oceanographic variables across two distant systems (3204 km apart) in the South Mid-Atlantic Ridge (both encompassed by marine protected areas—MPAs), we found that temporal alignment in environmental conditions was associated with coordinated shifts in counts of nine reef fish populations in each study area. Among the evaluated variables, pH emerged as the most influential factor. Despite the divergent responses among reef fishes, possibly reflecting differences in physiological plasticity, shared temporal patterns in pH appeared central to parallel population patterns observed across assemblages. Increases in sea surface height and chlorophyll-a played secondary roles, potentially benefiting some populations, although such effects may be transient. These results suggest that climate-driven convergence in environmental conditions can override geographic isolation, promoting similar biological responses that may reduce resilience and increase extinction risk. Given that both islands are legally protected, our findings highlight that even MPAs are not insulated from large-scale oceanographic stressors, underscoring the need for long-term monitoring and adaptative conservation strategies for remote reef systems.
Continue reading ‘Responses of reef fish populations to similar environmental changes across distant oceanic islands’Effects of long-term exposure to ocean acidification on the Patagonian scallop Zygochlamys patagonica (P.P. king, 1832), a strategic fishery resource in the Southwest Atlantic ocean
Published 12 March 2026 Science ClosedTags: biological response, dissolution, fisheries, laboratory, mollusks, morphology, mortality, South Atlantic
Highlights
- Scallops were resilient to low pH within the present range of natural variability.
- Negative impacts were observed under true ocean acidification scenario, including:
- Increased mortality & decreased shell mass condition index
- Dissolution of the external shell surface modifying shell ornamentation
- Shell disarticulation leading to the lost ability to swim
- During depuration time were observed:
- A recovery of the scallops’ vital functions when the stressor (low pH) was not present
- No recovery for shell mass condition index, shell ornamentations and disarticulated scallops
- No new disarticulated scallops
Abstract
Ocean acidification (OA) is a global process leading to a decrease in seawater pH. It is a direct consequence of the increase in CO2 emissions due to human activities with documented impacts on marine species and ecosystems. Effects of a long-term OA exposure (6 months) followed by a 2 months depuration period were evaluated on the Patagonian scallop Zygochlamys patagonica, an important seafood species of the Southwest Atlantic Ocean. Scallops were exposed to three target pHs, (1) pH 7.93, the mean annual pHT at the sampling site, (2) pH 7.83, the minimum value of the natural variability recorded at the sampling site and, (3) pH 7.53, a 0.3 pH unit below the minimum pH. Mortality, shell growth, and shell mass, adductor muscle mass and gonadal mass condition indices were measured at the beginning of the experiment and after 3, 6 and 8 months of exposure. Decreased pH led to a significant increase in mortality and decrease in the shell mass condition index. Shell growth was minimal over the course of the experiment with no effect of pH. The external shell surface showed a gradual dissolution and discolouration over the 6 months exposure to low pH. Shell disarticulation due to ligament damage was also observed in 29% of the animals exposed to low pH after 6 months resulting in loss of swimming ability of scallops, whereas no disarticulated animals were recorded in the high pH treatment. These results show the vulnerability of this species to future OA conditions with implications for the ecosystem services it provides, such as a decline in scallop numbers, greater vulnerability to predation and lower quality of commercial products.
Continue reading ‘Effects of long-term exposure to ocean acidification on the Patagonian scallop Zygochlamys patagonica (P.P. king, 1832), a strategic fishery resource in the Southwest Atlantic ocean’Linking surface pCO2 variability to physical processes along a continental shelf–ocean transect in the southwestern Atlantic Ocean during austral autumn and winter
Published 17 February 2026 Science ClosedTags: chemistry, field, South Atlantic
The southwestern South Atlantic Ocean is an important global sink of atmospheric carbon dioxide (CO2), driven by increased primary productivity in a nearby region where oligotrophic warm currents converge with nutrient-rich cold waters. However, uncertainties remain regarding CO2 dynamics and the role of physical processes in CO2 uptake across this region. Here, we assess variations in surface partial pressure of CO2 (pCO2) and air–sea CO2 fluxes in the Southwest Atlantic, along a transect from the continental shelf to the open ocean at 34.5°S during austral autumn 2018 and winter 2019. High-resolution spatial measurements of the temperature, salinity, and molar fraction of surface CO2 were conducted. In autumn 2018, the shelf region acted as a source of CO2 to the atmosphere (median of 3.2 mmol CO2 m-2 d-1), which was partially offset by a sink (median of –2.5 mmol CO2 m-2 d-1) in the open ocean. In contrast, the entire transect in winter 2019 presented median CO2 emissions of ~1.5 mmol CO2 m-2 d-1, which differs from climatological estimates. The spatial and seasonal variations in surface ocean pCO2 were linked to variable hydrodynamic processes, including water masses and mesoscale structures. Our findings reveal that, in one of the most productive oceanic waters worldwide, pCO2 may be influenced by distinct continental inputs (e.g., rivers, runoff, and groundwater discharge) and water masses (e.g., Tropical Water, Plata Plume Water and Subtropical Shelf Water). Therefore, the local hydrodynamic processes can modulate high spatial and seasonal variability in CO2 exchange at the ocean–atmosphere interface, with potential implications for regional and global carbon budgets. General results, such as climatological, cannot fully capture the influence of regional upwelling and continental water input, which highlights the importance of high-resolution regional observations.
Continue reading ‘Linking surface pCO2 variability to physical processes along a continental shelf–ocean transect in the southwestern Atlantic Ocean during austral autumn and winter’Resilience of pH to seasonal change in a large subtropical lagoonal estuary
Published 5 December 2025 Science ClosedTags: biogeochemistry, chemistry, field, South Atlantic
Highlights
- The lower Patos Lagoon Estuary displays a broad range of alkalinity and pH values, with riverine inputs marked by low buffering capacity.
- A critical period of corrosive conditions occurs from winter to mid-spring, likely driven by enhanced respiration and/or external CO₂ inputs.
- The estuary operates as a moderate to weakly buffered system, exhibiting aragonite undersaturation even under medium to high salinity conditions.
- pH sensitivity to environmental drivers is highest in summer and winter, whereas autumn presents the most uniform seasonal response.
Abstract
Coastal ecosystems exhibit a wide range of pH trends, from −0.023 to 0.023 pH units yr−1, making them particularly susceptible to acidification or basification. These variations are primarily driven by ecosystem metabolism and the influence of oceanic and riverine endmembers, as observed in the subtropical system of the Patos Lagoon Estuary (PLE, southern Brazil), where biogeochemical variability is largely governed by mixing of water masses with different properties. This study provides the first quantification of the seasonal variability of pH buffering capacity in the inner and outer zones of PLE. From May 2017 to September 2023, we assessed temporal variability using multiple approaches: (i) carbonate system parameters, (ii) sensitivity factors, (iii) buffering capacity of pH to fractional change of dissolved inorganic carbon (βDIC), (iv) metabolic effects on pH, and (v) environmental drivers of pH. The results revealed a distinct seasonal pH pattern, especially between summer with winter and spring, with consistently higher values at the outer station compared to the inner station, though spatial differences were not statistically significant. In winter and particularly in early spring, calcium carbonate (CaCO3) dissolution prevailed due to riverine input characterized by low buffering capacity. Along the salinity gradient, pH exhibited a pronounced difference, particularly between low and high salinity conditions. However, the persistent negative deviation of the metabolic effect on pH throughout the year and in salinity ranges, even under seawater conditions, supports the characterization of this coastal ecosystem as a net CO2 source, with especially high variability at mid-salinity conditions. Although the salinity gradient was comparable between stations, they exhibited differences in the magnitude of pH sensitivity to seasonal biogeochemical changes. These findings indicate that PLE functions as a system with moderate to low buffering capacity, with the outer zone showing greater resilience to pH fluctuations.
Continue reading ‘Resilience of pH to seasonal change in a large subtropical lagoonal estuary’Microplastic exposure under future oceanic conditions further threatens an endangered coral, Acropora cervicornis
Published 22 September 2025 Science ClosedTags: biological response, BRcommunity, corals, laboratory, morphology, multiple factors, photosynthesis, physiology, phytoplankton, plastics, South Atlantic, temperature
Microplastic pollution is ubiquitous in the oceans. However, little is known about the physiological impact of microplastics on corals, particularly under predicted future ocean conditions. This study investigated the individual impacts of microplastic exposure (MP) and predicted future ocean conditions [ocean acidification and warming (OAW)] as well as the combination of these stressors (OAW+MP) on the growth and physiology of Acropora cervicornis, a threatened Caribbean coral and its associated symbiont, Symbiodiniaceae. After 22 days, the OAW+MP treatment resulted in more pronounced physiological changes than either stressor individually or the control. OAW conditions alone had minimal impacts, despite A. cervicornis generally being sensitive to thermal stress. The OAW+MP treatment and the MP treatment also disrupted the host-symbiont relationship evidenced by the higher symbiont densities relative to the control and the OAW treatments. Additionally, the OAW+MP treatment resulted in lower chlorophyll a per symbiont cell. Microplastic handling is energetically costly, possibly leading to changes in host-symbiont signaling. Photosynthetic efficiency was only marginally lower in the OAW+MP treatment, and values did not indicate photosystem damage. Negative host health impacts were found with the OAW+MP treatment exhibiting lower skeletal growth compared to the control and lower host protein concentrations compared to the OAW treatment. These results indicate that although short term microplastic exposure alone may not pose a significant threat to coral health, when adding additional stressors, it can further threaten the health and recovery of this already vulnerable species.
Continue reading ‘Microplastic exposure under future oceanic conditions further threatens an endangered coral, Acropora cervicornis’Effect of short-term exposure to ocean acidification on antioxidant response in the Patagonian scallop Zygochlamys patagonica (P.P. King, 1832) from the Southwest Atlantic Ocean
Published 19 September 2025 Science ClosedTags: biological response, laboratory, mollusks, physiology, South Atlantic
Ocean acidification (OA) can impair antioxidant responses in bivalves altering their capacity to cope with environmental changes. Here, we analyzed the effects of short-term OA exposure on antioxidant responses of an important commercial Patagonian scallop Zygochlamys patagonica (P.P. King, 1832), considering present pH variability at natural beds of scallops and OA conditions. The scallops were exposed at three levels of pH, (1) high pHT = 8.10 (mean annual pH at the sampling site), (2) medium pHT = 7.80 (minimum value of natural variability recorded at scallops’ bed close to the sampling site), and (3) low pHT = 7.50 (0.30 below medium pH value) for 4 and 17 days of experimental time. Oxidative damage and antioxidants were measured in hemolymph, gill, and mantle. Hemolymph did not show signs of oxidative damage thus, antioxidant response induction was not detected under OA exposure. Gills showed antioxidant activation at 4 days under OA which decreased by the end of the experiment, with no signs of oxidative damage. Non-enzymatic antioxidant decreased under OA in the mantle. This study supports previous evidence of bivalves’ capacity to maintain their redox homeostasis under experimental OA conditions and constitutes a cornerstone to continue elucidating this species’ strategies to cope with environmental changes.
Continue reading ‘Effect of short-term exposure to ocean acidification on antioxidant response in the Patagonian scallop Zygochlamys patagonica (P.P. King, 1832) from the Southwest Atlantic Ocean’Impacts of ocean acidification on survival of the brown mussel (Perna perna) in Brazil
Published 27 August 2025 Science ClosedTags: adaptation, biological response, fisheries, growth, laboratory, mollusks, morphology, mortality, otherprocess, South Atlantic
The impacts of ocean acidification (OA) on seafood are recognized globally as a major threat, and OA is explicitly mentioned in the United Nations 2030 Agenda for Sustainable Development. One target of Goal 14 (SDG 14.3), life below water, is to minimize and address the impacts of OA using all levels of scientific cooperation. In 2018, the International Atomic Energy Agency launched a Coordinated Research Project (CRP), which gathered researchers from 13 different countries and aimed to evaluate the quantitative and qualitative impacts of OA on seafood. The Brazilian brown mussel Perna perna (Linné, 1858) was selected as the target species for these experiments. Low pH can disrupt the life cycle, affect survival and growth rates, and lead to a decline in mussel populations over time. Based on an agreed protocol within the CRP network, brown mussels were exposed to pH scenarios covering the present and future range of pH variability at the sampling site. The impacts on mortality, growth rate, and morphological parameters of juvenile mussels (seed) were evaluated after a 15-wk exposure in the laboratory, followed by an 8-wk recovery period in situ. Although no effect was detected for growth rate and allometric relationships during the laboratory experiment, mussel mortality was significantly higher at low pH. This effect on mortality disappeared when mussels were transferred to the field for a recovery period, and the acclimation to low pH had no carry-over effect on growth, allometric relationships, or sensory quality. Evidence of impacts from chronic lowering of pH is still needed to address species adaptation for long-term changes, which limit the prognostic power of short-term experiments.
Continue reading ‘Impacts of ocean acidification on survival of the brown mussel (Perna perna) in Brazil’Ocean acidification impairs growth and induces oxidative stress in the macroalgae Ulva fasciata and Petalonia fascia
Published 22 July 2025 Science ClosedTags: algae, biological response, growth, laboratory, photosynthesis, physiology, South Atlantic
Ocean acidification (OA), driven by increasing anthropogenic CO2 uptake, poses a significant threat to marine ecosystems; understanding the physiological responses of key primary producers like macroalgae is crucial for predicting ecological consequences. This study investigated the impacts of OA on two common intertidal macroalgae, the green alga Ulva fasciata and the brown alga Petalonia fascia, aiming to determine the effects of decreased seawater pH on their relative growth, photosynthetic performance, biochemical composition, and oxidative stress responses. Algae were exposed for 15 days to three pH levels (8.2, 7.4, and 6.5), and measurements included relative growth rate, membrane damage, total chlorophyll, soluble protein and sugar content, chlorophyll a fluorescence parameters, H2O2 content, lipid peroxidation, and activities of superoxide dismutase and catalase. Results showed that decreasing pH significantly reduced RGR in both species, particularly at pH 6.5, with U. fasciata generally exhibiting higher growth. Photosynthetic efficiency and total chlorophyll content declined under lower pH, while non-photochemical quenching generally increased. Both species exhibited increased membrane damage, H2O2 content, and TBARS levels at lower pH, indicative of oxidative stress. Antioxidant enzyme activities were significantly modulated by pH and showed species-specific patterns, with significant interactions between pH and species observed for most parameters. For instance, U. fasciata maintained higher Fv/Fm at pH 6.5, whereas P. fasciata often showed higher antioxidant enzyme activity; soluble protein and sugar contents were also significantly altered. These findings indicate that both Ulva fasciata and Petalonia fascia are susceptible to detrimental effects from simulated OA, suggesting potential shifts in the competitive balance and structure of intertidal macroalgal communities.
Continue reading ‘Ocean acidification impairs growth and induces oxidative stress in the macroalgae Ulva fasciata and Petalonia fascia’Stage-dependent life-history, physiological, and behavioral responses to low pH in an estuarine crab
Published 18 July 2025 Science ClosedTags: adaptation, biological response, crustaceans, laboratory, mortality, otherprocess, performance, physiology, reproduction, South Atlantic
Highlights
- We assessed the effects of low pH on larval stages of the crab Neohelice granulata.
- Low pH affects intermolt period, mortality, and oxygen consumption.
- Low pH also impacts swimming velocity and distance traveled.
- Marine larval stages were more adversely affected than the exported (first) larval stage.
Abstract
Early stages of marine invertebrates are vulnerable to ocean acidification. We investigated low pH effects on larval stages of the crab Neohelice granulata. We hypothesized that Zoea I, adapted to fluctuating environments, would show greater resilience than Zoea II and III, which develop in stable nearshore areas. We assessed pH 8 -control-, pH 7.5, and pH 6.9 effects on intermolt duration, mortality, oxygen consumption, and swimming behavior. Zoea I tolerated low pH with no changes in development or mortality, though oxygen consumption decreased at pH 6.9. In contrast, Zoea II and III showed delayed development, higher mortality, and reduced oxygen consumption at pH 6.9. While Zoea I showed no changes in swimming, Zoea II and III exhibited reduced swimming velocity and distance traveled under acidified conditions. These findings show that Zoea II and III are more sensitive to low pH, while Zoea I is more resilient.
Continue reading ‘Stage-dependent life-history, physiological, and behavioral responses to low pH in an estuarine crab’Biogeochemical parameters collected and analysed during the French cruises of the PIRATA programme in the Guinea Gulf, 1997–2024
Published 23 June 2025 Science ClosedTags: biogeochemistry, chemistry, field, South Atlantic
This paper presents a biogeochemistry dataset derived from the French component of the PIRATA (Prediction and Research Moored Array in the Tropical Atlantic) program in the Gulf of Guinea. This program, which started in 1997 with the deployment of a buoy network, has offered the opportunity to collect seawater biogeochemistry parameters since 2004. The measured parameters include salinity, dissolved oxygen, nutrients (since 2004), phytoplankton pigments (since 2011), marine pH (since 2021) and total alkalinity (since 2023). Following rigorous procedures, we provide high-quality data for studying the spatial and temporal variability of these parameters, with the aim of gaining a better understanding of the underlying processes that drive the ocean’s biogeochemical cycles in the Tropical Atlantic. The data are available in the SEANOE repository, which is accessible for scientific data in the marine sciences.
Continue reading ‘Biogeochemical parameters collected and analysed during the French cruises of the PIRATA programme in the Guinea Gulf, 1997–2024’Extreme compound events in the equatorial and South Atlantic
Published 24 April 2025 Science ClosedTags: chemistry, field, review, South Atlantic
The impacts of marine heatwaves (MHWs) on marine ecosystems can be amplified when combined with other extreme events. Here, we investigate the spatiotemporal evolution of compound events of MHW, high acidity and low chlorophyll in the equatorial and South Atlantic, using observation-based datasets and reanalysis products. We show that the frequency and intensity of these triple compound events under a fixed baseline have increased dramatically over the past two decades, peaking in the most recent years. We analyse the drivers of triple compound events for six regions and find that, for the Angola Front and Brazil-Malvinas Confluence regions, these events are associated with a poleward shift of the fronts. In the Agulhas Leakage region, an increase in warmer waters entering from the Indian Ocean leads to compound extremes. In the western equatorial and subtropical Atlantic, they are caused by changes in the air-sea heat fluxes, while in the eastern equatorial by a weakening of upwelling. In addition, triple compound events are widespread over the South Atlantic during El Niño events, which is important because MHWs can be predicted when associated with ENSO.
Continue reading ‘Extreme compound events in the equatorial and South Atlantic’Between shells and seas: effects of ocean acidification on calcification and osmoregulation in yellow clam (Amarilladesma mactroides)
Published 14 March 2025 Science ClosedTags: biological response, laboratory, mollusks, multiple factors, physiology, salinity, South Atlantic
Highlights
- Decline in ocean pH due to increased CO2 is threatening the physiology of marine organisms.
- Yellow clams (Amarilladesma mactroides) were exposed to ocean acidification and hypersaline stress for 96 hours to assess biomarkers of calcification and osmotic balance.
- OA reduced Ca2+-ATPase activity in the mantle, damaging mineralized structures.
- Elevated salinity increases carbonic anhydrase and Na+/K+-ATPase activity in the gills.
- Increased carbonic anhydrase activity in the mantle may help maintain acid-base balance in the species.
Abstract
The decline in ocean pH due to rising CO2 levels is a critical factor impacting marine ecosystems. Ocean acidification (OA) is expected to negatively affect various organisms, particularly those with mineralized structures. While the effects of OA on the calcification of shells and exoskeletons are documented, the impact on homeostatic processes, such as osmoregulation, is less understood. Osmoregulation is vital for maintaining water and salt balance within marine organisms, crucial for their survival and physiological functions. Acidification may alter ion exchange mechanisms, affecting the regulation of ions. In this study, we evaluated the effects of intermediate OA (pH 7.6) with or without hypersaline stress (35‰) on calcification and osmotic balance biomarkers in the bivalve Amarilladesma mactroides after 96 hours of acute exposure. We found that pH did not affect hemolymph osmolality or extracellular Ca2+ concentration. However, OA impaired the bivalve’s ability to maintain its mineralized structures by decreasing Ca2+-ATPase enzyme activity in the mantle. The increase in carbonic anhydrase activity indicated a specific response to maintain acid-base balance in the tissue, i.e., compensating for the effects of acidification by neutralizing CO2 accumulation and stabilizing internal pH. In the gills, both enzymes showed increased performance under higher salinity and reduced pH. Exposure to less alkaline pH inhibited carbonic anhydrase and Na+/K+-ATPase activity, potentially affecting the regulation of essential inorganic osmolytes.
Continue reading ‘Between shells and seas: effects of ocean acidification on calcification and osmoregulation in yellow clam (Amarilladesma mactroides)’Biomarkers responses in the amphipod Tiburonella viscana exposed to the biocide DCOIT and CO2-induced ocean acidification
Published 10 March 2025 Science ClosedTags: biological response, crustaceans, laboratory, multiple factors, physiology, South Atlantic, toxicants, zooplankton
Highlights
- Biomarkers responses in amphipods assessed in sediment testing with the biocide DCOIT;
- Environmentally relevant concentrations of DCOIT produced biomarker responses;
- Enzymatic activities of GST and AChe were reported, including LPO and DNA damage;
- Biomarkers responses were observed in CO2-induced acidification conditions.
Abstract
Anthropogenic carbon dioxide emissions (CO2) have led to climate change and marine acidification, with an estimated decrease in ocean surface pH of 0.3-0.4 units by the end of the current century. Chemical pollution also contributes to biodiversity loss in marine environments. This issue is particularly critical in areas under pressure from shipping activities, where the introduction of new antifouling system formulations poses a major threat to non-target species. The biocide DCOIT is the most widely used alternative to organotin compounds due to its rapid degradation in seawater. The toxicity of waterborne DCOIT to marine organisms has been documented, but sediment-bound effects are limited to apical responses and pH scenarios corresponding to current levels. In this study, we determine in a combined way, the toxicity of DCOIT under marine acidification scenarios assessing biomarker responses in the burrowing amphipod Tiburonella viscana as a parameter of sublethal effects in solid phase exposures. Environmental relevant concentrations of DCOIT caused inhibition of the enzyme glutathione S-transferases (GST), changed acetylcholinesterase-like activity (AChE), and increased DNA damage at pHs of 7.7 and 7.4. For lipid peroxidation (LPO), increased levels caused by DCOIT were found for both control (8.1) and intermediate (7.7) conditions of pH. Our data provides evidence of oxidative and genotoxic effects induced by DCOIT, with activation of detoxification and defense mechanisms in T. viscana. These results are important for ecological risk assessment and managing of antifouling paint biocides in multiple stressors scenarios.
Continue reading ‘Biomarkers responses in the amphipod Tiburonella viscana exposed to the biocide DCOIT and CO2-induced ocean acidification’Carbon dioxide–induced acidification enhances short-lived brominated hydrocarbons production in oligotrophic oceans
Published 18 February 2025 Science ClosedTags: biogeochemistry, biological response, community composition, field, Indian, multiple factors, nutrients, otherprocess, physiology, phytoplankton, South Atlantic
Oceanic emission is a primary source of brominated very short-lived substances (BrVSLs) to the atmosphere, which have important effects on stratospheric ozone chemistry. Marine biogeochemical processes regulating BrVSLs are often sensitive to ocean acidification. Yet, the response of BrVSLs production to acidification remains poorly understood. Herein, the effects of acidification on the production of two main BrVSLs, dibromomethane (CH2Br2) and tribromomethane (CHBr3), were studied by ship-based incubation experiments at three stations in the South Atlantic and Indian Oceans. The average CH2Br2 and CHBr3 concentrations increased by 17.2–58.7% and 14.3–80.3% due to acidification under the in situ nutrient conditions with nutrient and/or iron limitation at the three stations, but the mechanisms driving these increases varied among different regions. The increased bromoperoxidase (BrPO) activity caused by acidification facilitated BrVSLs release in the Eastern Tropical Indian Ocean, where diatoms were dominant. CHBr3 increased due to acidification as a result of enhanced reactivity of dissolved organic matter (DOM) in the Eastern Tropical Atlantic, where dinoflagellates were dominant. Brominated very short-lived substances increased due to acidification as a result of a combined effect of the above two mechanisms in the Benguela Current Coastal with high phytoplankton abundance. Under the nutrient and/or iron addition conditions with nutrient and iron sufficiency, however, acidification did not promote BrVSLs production due to its only minor effect on the BrPO activity and reactivity of DOM, partly because the effect of increased oxidative stress was offset by that of changed phytoplankton composition. Our study provided a basis for future modeling on the impact of acidification on global BrVSLs emissions.
Continue reading ‘Carbon dioxide–induced acidification enhances short-lived brominated hydrocarbons production in oligotrophic oceans’Effect of seawater acidification on energy metabolism in the hydrocoral Millepora alcicornis: inhibition of citrate synthase activity indicates disruption in aerobic pathways
Published 10 February 2025 Science ClosedTags: biological response, cnidaria, laboratory, mesocosms, physiology, South Atlantic
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.
Continue reading ‘Effect of seawater acidification on energy metabolism in the hydrocoral Millepora alcicornis: inhibition of citrate synthase activity indicates disruption in aerobic pathways’Short-term negative effects of seawater acidification on the rhodolith holobionts metatranscriptome
Published 7 February 2025 Science ClosedTags: algae, biological response, BRcommunity, community composition, laboratory, molecular biology, otherprocess, prokaryotes, South Atlantic
Highlights
- Cyanobacteria dominate the microbial community in living rhodoliths.
- Vibrionales dominate dead rhodolith skeletons.
- Short-term (1 h) acidification affects the microbial community structure.
- Diverse functional genes modulate microbe-host interactions.
Abstract
Rhodolith holobionts are formed by calcareous coralline algae (e.g., Corallinales) and associated microbiomes. The largest rhodolith bank in the South Atlantic is located in the Abrolhos Bank, in southwestern Brazil, covering an area of 22,000 km2. Rhodoliths serve as nurseries for marine life. However, ocean acidification threatens them with extinction. The acute effects of high pCO₂ levels on rhodolith metatranscriptomes remain unknown. This study investigates the transcriptomic profiles of rhodoliths exposed to short-term (96-h) high pCO₂ levels (up to 1638 ppm). Metatranscriptomes were generated for both dead and alive rhodoliths (15.48 million Illumina reads in total). Alive rhodoliths showed an enrichment of gene transcripts related to environmental stress responses and photosynthesis (Cyanobacteria). In contrast, the metatranscriptomes of dead rhodoliths were dominated by heterotrophic (Proteobacteria and Bacteroidetes) metabolism and virulence factors. The rhodolith holobiont metatranscriptomes respond rapidly to short-term acidification (within 1 h), suggesting that these holobionts may have some capacity to cope with acute acidification effects. However, the negative impacts of prolonged ocean acidification on rhodolith health cannot be overlooked. Rhodoliths exposed to low pH (7.5) for 96 h exhibited a completely altered transcriptomic profile compared to controls. This study highlights the plasticity of rhodolith transcriptomes in the face of ocean acidification and climate change.
Continue reading ‘Short-term negative effects of seawater acidification on the rhodolith holobionts metatranscriptome’
