Coastal habitats are increasingly affected by climate change and human-driven local pollution. Stressors as ocean warming, declining oxygen and pH levels are significant threats to vulnerable organisms, particularly tropical corals that inhabit narrow environmental ranges. Understanding coral growth and physiological responses to these stressors, along with the interspecific sensitivity among coral species is essential for predicting future coral reef structures. Our research involved experiments conducted under various manipulated conditions using local reef-building coral species collected from the southern Gulf of Thailand. The representative corals were subjected to stress conditions, including elevated temperatures, high light intensities, low oxygen, and pH levels. We quantified physiological parameters such as photosynthetic efficiency, Symbiodiniaceae and chlorophyll content, primary production, respiration, calcification biomass and growth rate. Our findings revealed varying sensitivity among coral species, with physiological responses according to the specific stressors. Temperature and light stress caused significant photoinhibition, resulting in reductions of Symbiodiniaceae density, chlorophyll concentration, and overall coral growth. Low oxygen levels significantly affected coral energy balance whereas and low pH influenced to structural integrity, causing acute impacts on more sensitive coral species. These insights into coral mechanism at biological and cellular levels are crucial for understanding how coral reefs will cope with the challenges posed by climate change.

How to cite: Yucharoen, M., Long, Y., Sinutok, S., Buapet, P., and Chotikarn, P.: Coral physiological trait responses to environmental stress in a changing ocean, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-52, https://doi.org/10.5194/oos2025-52, 2025.

Examining the consequences of worldwide climate change on fisheries is essential as it directly impacts the well-being of marine ecosystems, the sustenance of millions of individuals, and the security of global food supplies. Thus, understanding these impacts is crucial for developing adaptive management strategies for sustainable fisheries. This study aimed a comprehensive analysis on the potential responses of apex pelagic predators inhabiting in the Indian and South Atlantic oceans in response to changing climate conditions. The study analyzed sea surface temperature, salinity, and chlorophyll levels to predict species' impact by the end of the 21st century using a generalized additive model in response to normal and extreme conditions. Significant shifts in the mean temperature of catch (MTC) were forecasted for all species inhabiting the Indian and South Atlantic oceans under extreme climatic conditions (potential adaptation), but no changes in MTC were expected under normal conditions. All the species from both oceans exhibited a tendency to shift their distribution latitudinally (southward) in response to extreme conditions, while shifting longitudinally (wither east or westward) under normal conditions (potential tropicalization). In addition, South Atlantic species were predicted to experience higher latitudinal and longitudinal displacements (33-1125 kms, and 11-724 kms) compared to those in the Indian Oceans (33-679 kms, and 45-468 kms), in normal to extreme conditions. Present study suggests that, tropical Indian ocean species like bigeye, skipjack, yellowfin tuna, swordfish and marlins are less susceptible to climate change due to higher SST preferences, while temperate Indian ocean species like albacore and southern-bluefin tuna are more vulnerable compared to their counterparts in the South Atlantic ocean under changing climatic conditions. The study's results can enhance comprehension of the potential consequences of climate change on marine species, provide guidance for conservation strategies, and assist in the development of adaptive management practices for sustainable fisheries in global oceans.

How to cite: Mondal, S. and Lee, M.-A.: Impact of Global Climate Change on Apex Pelagic Predators of the World's Oceans: Potential Adaptation or Tropicalization , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-74, https://doi.org/10.5194/oos2025-74, 2025.

Ocean acidification (OA) is a global process decreasing seawater pH. It is a direct consequence of the increase in CO₂ emissions due to human activities, with consequences for marine species and ecosystems. The effects of long-term OA exposure (6 months) followed by 2 months of depuration were analyzed. Mortality, shell growth, shell mass, adductor muscle mass and, gonadal mass condition indexes (CI) were measured in the Patagonian scallop Zygochlamys patagonica, an important seafood of the Southwest Atlantic Ocean. The scallops were exposed at three levels of pH_T, (1) high pH_T: 8.004 ± 0.028 (mean annual pH_T at natural beds), (2) medium pH_T: 7.800 ± 0.067 (minimum value of natural variability recorded at the sampling site) and (3) low pH_T level (acidification treatment): 7.520 ± 0.070 (0.3 below minimum pH_T value found at natural beds). Individuals were analyzed at the beginning of the experiment (T0), 3, 6 and 8 months of experimental time. Scallop mortality rates were different between pH levels and experimental time, with no interaction. Mortality was higher at low pH as compared to high pH treatment, it was also significantly lower during the depuration period as compared to the OA exposure times (p<0.05). Shell growths did not show differences between pH treatments. Shell mass condition indexes at high pH did not differ over time. At low pH_, these indexes were significantly lower after 6 and 8 months as compared to other pH treatments and times (p<0.05). The external shell surface showed a gradual dissolution of the external part of the valve between T0 and 3 and 6 months of exposure to low pH. Shell disarticulation due to ligament damage was also observed in 30% of the animals in the low pH treatments after 6 months of OA exposure, as compared to 0% in the high pH treatment, resulting in loss of swimming ability of scallops under OA. Gonadal and adductor muscle condition indices showed no differences between pH treatments. Gonadal CI increased over time regardless of treatments, showing the natural process of gonadal maturation over time. These results show the vulnerability of this species to future OA conditions with the possible implications for the species' biological interactions and the ecosystem services it provides.

How to cite: Lomovasky, B., Yusseppone, M. S., Campodónico, S., Schwartz, M., Metian, M., and Dupont, S.: Impact of ocean acidification on the Patagonian scallop Zygochlamys patagonica, a key seafood species for the Southwest Atlantic Ocean, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-83, https://doi.org/10.5194/oos2025-83, 2025.

Research and investment into marine carbon dioxide removal (mCDR) have grown at a stunning pace in response to the Intergovernmental Panel on Climate Change’s 2022 assertion that removal of atmospheric carbon dioxide will be required to meet Paris Agreement goals for climate mitigation. Many scientific questions remain, including the possible influence of Earth system feedbacks on the efficiency of this technology. To fully explore the uncertainty space surrounding questions of mCDR efficiency, many plausible parameterizations of these feedbacks must be tested, which is an approach currently out of reach for traditional simulations due to computational constraints. As shifts induced in ocean carbon content due to the use of mCDR will generally be smaller than natural variability inherent to these systems and can therefore not be measured directly, developing methods for monitoring, recording, and verification (MRV) of carbon removal is an additional fundamental challenge in implementing gigaton-scale mCDR projects. Key to any MRV protocol will be models that represent physical, chemical, and biological processes with sufficiently small uncertainties and the lowest possible computational cost. In this work, I present an adapted version of the Ocean Circulation Inverse Model (OCIM) that includes biogeochemical processes relevant to mCDR. OCIM is advantageous in that it uses a transport matrix to simplify physical processes in the ocean, reducing computation time by orders of magnitude and requiring only the processing power available on a laptop. With this model, a suite of parameterizations of the CO2-biotic calcification feedback under different forcing scenarios is run to test our mechanistic understanding of this process and more fully constrain the possible inefficiency that this feedback could create in mCDR deployments. 

How to cite: Barrett, R. and Carter, B.: Using Inverse Modeling of Biogeochemical Processes to Constrain Uncertainty in Monitoring, Recording, and Verification for Marine Carbon Dioxide Removal, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-126, https://doi.org/10.5194/oos2025-126, 2025.

The transport of dissolved organic carbon (DOC) into aquatic ecosystems is causing a global darkening of coastal seas, negatively impacting water quality, light penetration, nutrient cycling, and overall ecosystem productivity. Climate change is expected to exacerbate brownification by altering catchment hydrology and increasing run-off, raising DOC levels and accelerating coastal darkening. Habitat-forming benthic macrophytes (e.g. seagrasses, macroalgae, aquatic plants) host high biodiversity and support a wealth of ecosystem service provision, including fishery support, water quality mitigation, coastal protection and blue carbon storage. However, their reliance on sunlight for photosynthesis makes them extremely vulnerable to coastal darkening and brownification. The decline of benthic macrophytes due to brownification would induce a cascade of significant ecological and socio-economic repercussions, so it is essential to understand how these ecosystems may respond. Using the Baltic Sea as a model system for future trends in brownification, we take a multidisciplinary approach to elucidate how the primary production of coastal habitats will change throughout this century. Working along a natural gradient of brownification spanning 10° of latitude, we have characterized underwater light fields, and quantified organismal photobiology and community habitat formation to model primary production under current and future brownification scenarios. By reconciling the organismal-community level effects of brownification on these valuable coastal ecosystems, we provide evidence-based support for coastal conservation and management strategies for both mitigating climate change and land-use change stressors and for maintaining coastal ecosystem services.

How to cite: Gonzalez-Guerrero, L. A., Kratzer, S., Norlund, L. M., and Burdett, H. L.:  Assessing the Impact of Coastal Darkening on Primary Production of Habitat Forming Macrophytes, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-189, https://doi.org/10.5194/oos2025-189, 2025.

The MoNITOR (Mitigation of Natural Incidence Towards an increased Oceanic Resilience) exemplifies the transformative power of international cooperation in building global resilience to coastal ecological disasters. Through a collaborative framework, MoNITOR establish a high-resolution physicalecological coupled operational numerical forecasting system for the ecological environment through multi-scale research and multi-disciplinary data and information cooperation investigations. This international partnership is essential to developing comprehensive ocean ecological forecasting systems, which offer critical insights and predictive products on marine ecosystems, effectively connecting data producers with end-users across nations. By fostering such international synergies, MoNITOR provides a strong scientific foundation to support the conservation and sustainable management of marine resources.

MoNITOR places particular emphasis on understanding the processes and mechanisms driving coastal ecological change, making marine ecological data more accessible and predictable worldwide. This shared knowledge enables the development and implementation of sustainable ocean solutions that contribute to ecosystem health and resilience. Furthermore, MoNITOR’s international collaborations significantly enhance coastal disaster prevention and mitigation capabilities, improving model accuracy and extending applications for ecological forecasting across global coastal areas. Through collaborative research, data sharing, and joint forecasting efforts, participating countries are collectively building a resilient future for coastal ecosystems and communities, underscoring the crucial role of international cooperation in sustainable ocean development and disaster readiness.

How to cite: Wang, Y., Fang, Y., and Sun, Q.: Mitigation of Natural Incidence Towards an increased Oceanic Resilience, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-233, https://doi.org/10.5194/oos2025-233, 2025.

Approximately 1,000 km³ of wastewater is generated globally each year, positioning sewage treatment plants as significant sources of dissolved organic carbon (DOC). The carbon sequestration potential of DOC from sewage effluents, particularly its transformation into recalcitrant forms, remains underexplored.Our study used Fourier transform ion cyclotron resonance mass spectrometry to examine the molecular composition of DOC, specifically carboxyl-rich alicyclic molecules (CRAMs), in effluents from sewage treatment plants (eSTP), river discharge outlets (RDO), and estuaries. Results revealed increases in O/C ratios, molecular complexity, and CRAMs as distance from the estuary grew, underscoring estuaries’ role in enhancing organic matter recalcitrance. Dark culture experiments also indicated substantial CRAM formation, though eSTP molecular composition remained stable. Microbial carbon pump (MCP) processes contributed to DOC transformation, underscoring microbial influence.We term the recalcitrant DOC in wastewater “gray carbon,” highlighting its sequestration potential and relevance in carbon trading. Further research on gray carbon’s composition, transformations, and role in blue carbon dynamics will support policies advancing carbon management, technology development, and carbon neutrality goals.

How to cite: Meng, Y., Du, X., and Jiao, N.: Gray Carbon in Effluent: Implications for Marine Carbon Sequestration, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-403, https://doi.org/10.5194/oos2025-403, 2025.

Atolls face risks from rising sea levels and reduced sediment supply from coral reefs, leading to accelerated erosion. This study examines Aldabra, a raised atoll and UNESCO World Heritage Site in the Indian Ocean, tracking shoreline changes against a regional sea level rise of 2–3 mm per year. Using aerial and satellite images from 1960 and 2011, 85% of Aldabra’s shoreline was analyzed. Over 51 years, 61% of the shoreline remained unchanged, while 24% changed at a low average rate of 0.25 ± 0.36 m per year. Erosion and accretion rates were nearly balanced, with significant localized changes, such as a lagoon shoreline transforming into a mangrove habitat. Critical erosion occurred at turtle nesting sites and the research station. The lagoon shoreline experienced more rapid changes than the ocean-facing side. Despite these dynamics, Aldabra's overall shoreline and land area remained stable, similar to other Indo-Pacific atolls, highlighting its adaptive capacity. This research underscores the need to minimize local impacts on sediment availability to preserve the natural dynamics and adaptation potential of reef islands. Continuous shoreline monitoring is essential for developing timely adaptation strategies to conserve Aldabra's unique ecosystem.

How to cite: Constance, A., Bunbury, N., Lack, N., Nebiker, S., Obura, D., Fleischer-Dogley, F., and Schaepman-Strub, G.: Low average shoreline change rate in 51 years on the raised Aldabra Atoll, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-450, https://doi.org/10.5194/oos2025-450, 2025.

The northwest coast of Africa, influenced by the Canary Current, is one of the most productive areas in the world, primarily due to the abundance of small pelagic fish. Upwelling brings high-nutrient sub-surface water to the surface, thus promoting the formation of abundant biomass and considerable fishery resources. Moreover, these upwellings bring sub-surface water high in dissolved inorganic carbon (DIC) with low pH to the surface, reducing the saturation of calcium carbonate and aragonite, making these areas vulnerable to ocean acidification. This can have adverse effects on calcifying marine organisms.  The objective of this study is to explore the links between hydrological parameters, carbonate system characteristics, and upwelling activity along the Moroccan Atlantic marine ecosystem between Cape Blanc (21°N) and Cape Cantin (33°N), a region where studies on ocean acidification remain very limited. Upwelling activity was widely observed throughout the study area during the spring season, while in autumn, it was restricted to specific areas, notably between Cape Cantin and Cape Ghir, Cape Draa, between Cape Boujdour and Dakhla, as well as at Cape Blanc, with latitudinal fluctuations. In terms of carbonate chemistry, they are marked by low pH_T-insitu, relatively low aragonite saturation, and high DIC concentrations. The intensification of the upwelling phenomenon in spring amplifies the negative ocean acidification state in coastal areas, notably by lowering the pH to 7.8 and reducing the aragonite saturation state to 1.2, thereby impacting the Moroccan upwelling ecosystem, with effects particularly pronounced in the Cap Blanc region. This work provides valuable insights into the carbonate system along the Moroccan Atlantic coast, laying a solid foundation for future research. A long-term biogeochemical analysis is essential to quantify acidification and understand its ecological consequences.

How to cite: Jamal, C., Makaoui, A., Chierici, M., Cervantes, D., Idrissi, M., Bouthir, F. Z., Ettahiri, O., Nait Hammou, H., Yousfi, S., and Bouamrani, M. L.: Seasonal Upwelling Effects on Seawater Carbonate Chemistry and Ocean Acidification in Northwest Africa, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-504, https://doi.org/10.5194/oos2025-504, 2025.

Reef-building corals, known for their heightened susceptibility to environmental shifts, are expected to experience deleterious repercussions after escalating climate change impacts. Despite the looming threats, the existing body of knowledge concentrates mainly on specific locations and does not fully explore inter- and intraspecific coral sensitivity across various reefs, leaving a substantial void in our comprehension of the broader ecological landscape. Through the TARA Pacific expedition,900 samples from Pocillopora spp. and Porites spp. were collected on 31 islands across the Pacific from 2016 to 2018 to assess the phenotypic signatures using a multi-biomarker approach. The biomarkers analyzed included biomasses of animals and symbiotic dinoflagellates to study the trophic status of the colonies, copies of mitochondrial DNA, and total carbohydrate content as indicators of metabolism and total antioxidant capacities and protein carbonylation as proxies for redox state and cellular damages. The analysis of the unprecedented wide dataset allows us to answer the following questions: (1) How do biomarker profiles vary within and between different species across the Pacific? (2) Which environmental factors correlate with the biomarker profiles? (3) Which biomarkers can be used to monitor coral reefs? The results revealed a broad plasticity phenotype and correlations to specific environmental parameters. Ultimately, this research seeks to provide conservationists with essential tools and insights to improve coral resilience and restoration efforts, thereby supporting sustainable strategies to safeguard these vital ecosystems against ongoing environmental challenges.

How to cite: Plichon, K., Furla, P., Zamoum, T., Arenas, S., Poullet, M., Forcioli, D., and Consortium, T. P.: Characterization of Coral Phenotype Plasticity Across the Pacific Ocean, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-653, https://doi.org/10.5194/oos2025-653, 2025.

Coral reefs face severe vulnerabilities to environmental fluctuations and are poised to endure adverse consequences amid escalating climate change impacts. However, current research remains confined to localized contexts, failing to provide a comprehensive understanding of how various coral species respond to these global stressors across macrogeographic scales. This knowledge gap inhibits a nuanced grasp of the broader ecological and evolutionary dynamics at play. During the TARA Pacific expedition from 2016 to 2018, we conducted an extensive study involving the collection of ~300 samples of Pocillopora spp. from 32 Pacific islands. Employing a multibiomarker methodology, our research delved into diverse phenotypic expressions, including metrics such as animal and symbiotic dinoflagellate biomass, metabolic indicators, and redox status. Furthermore, we amassed comprehensive genome-wide diversity and environmental data, facilitating the identification of genes and genetic regions pivotal to the adaptive response of these organisms to environmental fluctuations throughout the distribution area, as elucidated through Genetic Environment Association (GEA) and Genome-Wide Association Study (GWAS) analyses. Our investigation unveiled genotypes associated with fluctuations in sea surface temperature and unusual environmental conditions or physiological conditions associated to these fluctuations. By exploring the allelic diversity associated with each coral phenotype and its responsiveness to environmental cues, we describe differentiated adaptive responses among Pocillopora species even if they are often found in sympatry, a finding of crucial importance for the tailoring of conservation strategies Pacific Ocean coral reefs.

How to cite: Arenas, S., Poulet, M., Plichon, K., Zamoum, T., Consortium, T. P., Furla, P., and Forcioli, D.: Identifying the genetic basis of local adaptation to sea surface temperature variations in natural populations of Pocillopora spp reef building corals, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-655, https://doi.org/10.5194/oos2025-655, 2025.

Abstract:

Ocean deoxygenation represents one of the most significant alterations currently observed within marine ecosystems. Hypoxic events in the Eastern Boundary Upwelling Ecosystems (EBUE) have been shown to have substantial impacts on ecological and biogeochemical processes. Moreover, it is anticipated that the severity and frequency of oxygen depletion will increase progressively as a result of climate change.

Despite the Mauritanian coast being identified as one of the ‘‘hot spots’’ for coastal hypoxia, it has received less attention compared to other regions such as the Oregon Coast or the Baltic Sea. In this study, we examine a multi-decadal CTD dataset, including measurements of dissolved oxygen, along the north-south latitudinal gradient of the Mauritanian coast.

Climatologies were used to study the spatio-temporal variability (seasonal, interannual) of typical hypoxic events, as well as the less frequent anoxic events, at different depths. Our study reveals both spatial and temporal occurrences of hypoxia across various areas and layers in addition to considerable spatial variation and seasonal fluctuations in the dynamics of dissolved oxygen and temperature.

The outcomes of this study will contribute to a better understanding of this phenomenon and, ultimately, support the sustainable management of fisheries in Mauritania.

How to cite: Bouya, M., Llope, M., Chierici, M., Dall'Olmo, G., Tiedemann, M., and Licandro, P.: Spatio-temporal variability of hypoxic events in the Mauritanian upwelling system, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-753, https://doi.org/10.5194/oos2025-753, 2025.

Ocean acidification and its role in disrupting ecosystem dynamics has been extensively documented in contemporary marine science. Ocean acidification results from the oceans absorbing approximately one-third of all CO₂ released into the atmosphere generating downstream shifts in seawater carbonate chemistry. Governing bodies worldwide are incentivizing marine Carbon Dioxide Removal (mCDR) technologies to mitigate anthropogenic climate change. Among these strategies, Ocean Alkalinity Enhancement (OAE) has been proposed as a dynamic method to remove carbon and offset ocean acidification. However, OAE remains a ‘black box’ with many foundational questions still unanswered. There is growing evidence for potential co-benefits of OAE at the ecosystem level, but further research is needed to capture how OAE integrates at the organismal level. Here we present a novel dataset highlighting how naturally occurring alkalinity enhancement positively modulates coral physiology. Three biogeochemically distinct substrate types were identified in Bocas del Toro, Panama. Ten coral colonies of the branching species, Porites porites (n = 10), were deployed within 50 m x 50 m matrices in dense and sparse T. testudinum meadows (n = 3) as well as in intact coral communities (n = 3; >30% live coral cover). We found that belowground respiration within intact communities of T. testudinum generated an alkalinity-rich environment significantly increasing calcification and fitness. Perhaps most compelling is that this phenomenon persisted despite corals experiencing weak to moderate hypoxia (£ 4.5 mg L^-1) due to nighttime respiration.We believe this research provides critical evidence for how Ocean Alkalinity Enhancement could modulate organismal physiology in at-risk marine communities.

How to cite: Lowell, A., Kline, D., Lucey, N., Finelli, C., Altieri, A., Thacker, R., and Peterson, B.: Natural alkalinity enhances coral physiology and what this means for restoration, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-774, https://doi.org/10.5194/oos2025-774, 2025.

This paper examines the coastal vulnerability of the West African coasts. Coastal vulnerability is a significant concern in this region, where areas are increasingly exposed to the impacts of climate change. However, the factors contributing to this heightened vulnerability are varied and extend beyond just climate change. Key drivers include population growth, rapid urbanization, weak governance, and inadequate coastal management practices. The paper introduces the Coastal Vulnerability Index (CVI) as a useful tool for assessing and comparing coastal vulnerability across West Africa that can help identify the most vulnerable regions and the factors influencing their susceptibility. The Gulf of Guinea coast corridor, extending from eastern Côte d'Ivoire to northern Cameroon, is very vulnerable. In contrast, the region from eastern Sierra Leone to western Côte d'Ivoire is classified as having moderate to low vulnerability. It concludes that to protect the future West and Central African coasts, governments must develop and implement action plans, which should include strategies for relocation, adaptation to flood risks, restrictions on development in high-risk areas, and community initiatives aimed at reducing the impacts of coastal hazards. Additionally, socioeconomic growth and coastal migration should be monitored and managed sustainably. Immediate action is necessary to limit future coastal threats through effective adaptation measures.

How to cite: Dada, O. and Almar, R.: Coastal Vulnerability of West African Coasts under the Changing Climate and Human Development, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-995, https://doi.org/10.5194/oos2025-995, 2025.

Harmful phytoplankton blooms have growing impacts on ecosystems and human populations. In the context of warming waters and oceans, they are one of the main issues linking environmental, animal and human health.  We studied the toxic microalga Vulcanodinium rugosum, which produces pinnatoxins (PnTX) and portimines (Prtn). These toxins accumulate in marine organisms and are frequently detected worldwide. We characterized morphologically, genetically and on toxins level this dinoflagellate and studied its ecophysiology. Our results demonstrated its thermophilic and euryhaline features and its growth ranges between 20 and 30°C. Its ability to grow on an organic nitrogen source was showed. Its expansion in French Mediterranean lagoons was confirmed by the contamination of the mussels. The survival of this organism in the digestive tract of mollusks proves that the transfer of shellfish is potentially a source of contamination of new ecosystems. We also determined the distribution in relationship with environmental conditions in four French Mediterranean lagoons, the contamination by PnTX G and Prtn A of various marine organisms, the ecological impacts and the health risks. We showed that Vulcanodinium and toxins could contaminate a wide variety of marine species including bivalve mollusks, fish, gastropods and echinoderms. The kinetics of contamination and elimination in oysters showed that PnTX G persisted for a long time in bivalve mollusks’ tissues. The information and tools we developed should be of great interest to environmental and health monitoring managers. This study also led to questions concerning the general expansion of V. rugosum area, other species that could possibly be contaminated, sub-lethal impacts on marine organisms, and the chronic risks to humans inherent in persistent contamination in seafood products. Studies focusing on this dinoflagellate and its toxins are important, particularly in the context of warming waters favoring blooms on a global scale.

How to cite: Abadie, E., Bouquet, A., Rolland, J. L., Masseret, E., Felix, C., Chomerat, N., and Laabir, M.: Study of the neurotoxic  thermophilic dinoflagellate Vulcanodinium rugosum in French Mediterranean lagoons facing global change : morphogenetic and toxinic characterization, ecology and toxins transfer in trophic levels, risk to human health., One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1172, https://doi.org/10.5194/oos2025-1172, 2025.

This paper examines the integration of ocean acidification (OA) considerations into the European Union's Marine Strategy Framework Directive (MSFD). Ocean acidification, driven by the increase of CO₂ in ocean water, threatens marine biodiversity, fisheries, and economies across European waters, affecting ecosystems in the North-East Atlantic, Baltic, Black, and Mediterranean seas. This study identifies opportunities within MSFD descriptors, particularly Descriptor 5 (eutrophication) and Descriptor 7 (hydrographical conditions), to integrate OA parameters in ways that strengthen the EU’s goal of achieving Good Environmental Status (GES). The study further highlights the role of Regional Seas Conventions, such as OSPAR and HELCOM, as key platforms for coordinating OA monitoring and data-sharing across borders, promoting harmonized efforts to address OA impacts on marine ecosystems. By leveraging these collaborative networks, EU Member States can ensure that OA indicators and best practices are consistently applied, fostering more regionally coordinated responses to the challenges of OA. This paper also demonstrates that scientific data on OA can be effectively translated into policy actions through strategic MSFD integration, providing a valuable model for adapting marine policy to emerging environmental threats. By embedding OA-specific monitoring and mitigation within the MSFD framework, this research underscores how European nations can support ecosystem resilience, advancing sustainable marine management in a changing climate.

How to cite: Turner, J., Frosch, A., and Dressler, I.: Taking a regional ocean-based approach - Integrating Ocean Acidification into the European Union's Marine Strategy Framework Directive, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1261, https://doi.org/10.5194/oos2025-1261, 2025.

Since 2011 unprecedented quantities of holopelagic Sargassum morphotypes have been observed in the tropical Atlantic, resulting in economic, health, and ecological consequences. These events, characterized by large biomass aggregation spreading across the tropical Atlantic and later stranding along coastline, have been studied to understand the spatio-temporal variability of Sargassum morphotypes. While current models provide insights into the advection, there is little understanding on the mechanisms behind the response to current environmental conditions. In order to identify and explicitly quantify Sargassum’s trade offs between the changing ocean conditions, we developed a multi reserves DEB (Dynamic Energy Budget) model. Using the DEB framework, we simulate Sargassum’s nutrient uptake and thermal response under different environmental scenarios representing the conditions encountered by Sargassum along their drift. Parameters for the model are estimated and validated through comparison with experimental data.

As a part of the BIOMAS project (BIOenergetic Modeling Approach for Sargassum dynamics), this DEB model will be integrated into a drift model to simulate Sargassum sp. proliferation on a seasonal scale and across multiple years. This approach aims to improve our understanding of the interplay between the biological and physical factors driving Sargassum morphotypes dispersal and biomass proliferation. In such a manner, improving bloom predictions will support local communities by understanding Sargassum occurrences therefore mitigating the impacts of these events. 

How to cite: Lagunes, M. J., Lett, C., Berline, L., Salas-Acosta, E. R., Robledo, D., Vásquez-Elizondo, R. M., Thibaut, T., and Pecquerie, L.: Predicting growth and survival of holopelagic Sargassum using a mechanistic model under different environmental scenarios, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1269, https://doi.org/10.5194/oos2025-1269, 2025.

The frequency of tropical cyclones emerging from the Bay of Bengal and Arabian Sea has increased in the last ten years. In the Bay of Bengal, compared to 1990-2010 and 2010-2023, there is an increased occurrence of depression, inducing more cyclones of the “red alert” category than orange or yellow, which were more frequent in the past decade. Whereas in the Arabian Sea, comparing 1982-2002 and 2001-2019, the severe category of cyclones has increased by 150 per cent. The Arabian Sea is not prone to frequent tropical cyclones like the Bay of Bengal. However, this trend is changing with increased cyclone activity in the past five years. The cyclones are seen as an oceanic response to rapid warming and climate change. Another concerning hazard is the sea-level rise, which is predicted to be 19.2 centimetres or 0.64 feet by 2050 in the three most vulnerable coastal districts of Tamil Nadu. This was traced in the draft report prepared by the Centre for Climate Change and Disaster Management (CCCDM). Whereas between 1916 and 2015 the rise was 0.18 feet on the Chennai coast. A study by the Centre for Study of Science, Technology, and Policy (CSTEP) found that if CO2 emissions continued till 2050 followed by a fall till 2100, it would still lead to a rise of sea level to 74.9 centimetres or 2.45 feet in Kochi by 2100. In these two circumstances, the most impact has been on the coastal communities that rely on fishing, aquaculture, and agriculture face critical challenges such as displacement, livelihood threats, and health risks. To address this, the governments of Tamil Nadu and Kerala have taken measures. This includes disaster management plans, cyclone shelters, monsoon preparedness and response, early warning systems and relief activities. The coastal infrastructure and monsoon preparedness have been honed. However, in the relief and mitigation of coastal health, both lack measures. The major part of the relief has been played by civil society organisations in Tamil Nadu and individuals in Kerala. At the policy level, disaster management plans are present in both states; however, steps to reduce rapid urbanisation, ocean-based approaches for sustainable fishing and protection of coastal ecosystems are absent. For two reasons, I chose Tamil Nadu and Kerala as case studies. First, to analyse the impact of coastal issues and the impact of anomalies on society in both the east and west coasts. Second, to compare the coastal governance measures of governments on two coasts where Tamil Nadu in the east with the longest coastline is observed to be better in managing weather calamities along with other east coast states. I will analyse the major coastal issues of Tamil Nadu and Kerala. Second, the responses by the government and society to draw lessons from other regions (South Asia, Europe, and the Caribbean) within India (Gujarat) to better the coastal management. The study will lead to policy recommendations on the relevance of the ocean-based approach for healthy coasts. 

How to cite: Anandhan, P.: The challenge of disasters and sea level rise to the coastal communities: A case study of two states in India, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1404, https://doi.org/10.5194/oos2025-1404, 2025.

The number of studies investigating the effects of ocean acidification on marine organisms and communities increases every year. Results are not easily comparable since the carbonate chemistry and ancillary data are not always reported in similar units and scales and are not calculated using similar sets of constants. To facilitate data comparison, a data compilation hosted by the PANGAEA Data Publisher was initiated by the European Network of Excellence for Ocean Ecosystems Analysis (EUR-OCEANS) and the first large-scale European Project on Ocean Acidification (EPOCA) in 2008. It has been maintained within the framework of the International Atomic Energy Agency (IAEA) Ocean Acidification International Coordination Centre (OA-ICC) in collaboration with Xiamen University and the Laboratoire d'Océanographie de Villefranche (LOV), France, since 2013. By November 2023, a total of 1501 datasets (over 25 million data points) from 1554 papers had been archived. To easily filter and access relevant biological response data from this compilation, a user-friendly portal (https://oa-icc.ipsl.fr) was launched in 2018. Most of the study sites from which data have been archived are in the North Atlantic Ocean, North Pacific Ocean, South Pacific Ocean, and Mediterranean Sea, while polar oceans are still relatively poorly represented. Mollusca and Cnidaria are still the best-represented taxonomic groups. The biological processes most reported in the datasets are growth and morphology. Other variables that can potentially be affected by ocean acidification and are often reported include calcification/dissolution, primary production/photosynthesis, and biomass/abundance. The majority of the compiled datasets have considered ocean acidification as a single stressor, but their relative contribution has decreased from 68 % before 2015 to 57 % today, showing a clear tendency towards more data archived from multifactorial studies.

How to cite: Gazeau, F., Yang, Y., Brockmann, P., Galdino, C., Hansson, L., and Schindler, U.: OA-ICC data compilation and portal on the biological response to ocean acidification , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1408, https://doi.org/10.5194/oos2025-1408, 2025.

This presentation is a call for regional and international action. It focuses on a climate-driven situation in Africa that will evolve into a humanitarian crisis if little is done. Much of the Africa population is on the eastern side of the continent. Here some 60 M people live on the shoreline of the western Indian Ocean (WIO). These communities are highly dependent on the ocean for their food security, livelihoods and culture. The bulk of the WIO countries are considered the poorest of the poor and the least developed globally. The main food source comes from artisanal fisheries. Gears and fishing techniques are simple comprising canoes, fishing lines and nets. Nearly all fisheries in WIO are in decline from overfishing.

Added to this, significant scientific observations and data indicate WIO is warming, being one of the fastest developing hotspots in the global ocean. This knowledge has come from some 10 years of focused research producing 100s of publications using state-of-the-art techniques including ship surveys, marine robotics, satellites and models — as well as on the ground coastal community observations. Startling outputs indicate the tropical region of WIO will warm some 5°C by 2100 and suffer declines in biodiversity richness and fisheries of up to 70%. Moreover, marine heat waves are set to dominate almost 12 months of the year by 2035, and consequently, coral reefs that support artisanal fisheries, will be decimated. Together with the rapidly expanding human populations of 3% per annum and decline in ecosystems and fisheries — WIO faces a daunting challenge for coastal community survival.

Our new science is now focused on producing a more accurate climate-driven ‘road map’ of the future of WIO — the ocean, ecosystems, fisheries and impacts on people (food security) — using the latest computer technologies and models. These highlight tipping points that serve as vital targets for action.

But according to our first generation of models, the first big tipping point is soon (2035). Whilst we still need to pursue excellent science to produce the WIO climate road map, we also need to urgently begin thinking of mitigation strategies. We have enough understanding to respond. We clearly must work with conventional frameworks for action, i.e. get the WIO climate crisis on national and UN agendas. However, we also need to recognise that this framework is slow and cumbersome to respond. Because of the urgency of the WIO climate crisis — we suggest the assistance of a faster parallel-coupled framework. Motivated by the recently released statement from Ban Ki-moon "We need an urgent change of direction in global decision-making, with a bold new approach rooted in justice and dignity. We need ‘long-view leadership", we suggest this parallel-coupled approach includes: (1) scientists actively driving the regional and international agenda, (2) a fresh dynamic Science-to-Policy mediator such as IPOS (International Panel for Ocean Sustainability) to intervene, (3) our project organizes two UN-AU Summits on the WIO climate crisis, and (4) we work on the ground with communities to find solutions and mitigations.

How to cite: Roberts, M.: The (hidden) Western Indian Ocean Climate Crisis — A need for urgent action, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1162, https://doi.org/10.5194/oos2025-1162, 2025.

Pelagic ecosystems span the world's oceans and support a wide range of species, from iconic predators such as sharks and rays to essential fisheries resources, including offshore top predators such as tuna and swordfish, as well as small coastal forage fish such as anchovies and sardines. Equally important, though less visible, are mesopelagic organisms, which contribute to carbon export and regulate the entire pelagic ecosystem. Characterised by a strong vertical structure, horizontal variability, and temporal changes, pelagic ecosystems pose significant challenges for global-scale modelling, further complicated by the lack of comprehensive, synoptic observations to calibrate these models.

As climate change rapidly alters ocean conditions, its impacts on pelagic ecosystems are becoming more pronounced, highlighting the urgent need to deepen our understanding of their response to environmental changes and human pressures. While current ecosystem models have predicted shifts in the spatial distribution of fish and declines in their global biomass, many uncertainties remain regarding the mechanisms that actually drive ecosystem structure and trophic interactions.

Here, we use the mechanistic model APECOSM to simulate six generic pelagic communities spanning from the surface to 1,000 metres depth: small and medium-sized epipelagic, tropical tuna, mesopelagic migrant, mesopelagic resident, mesopelagic feeding tuna, and small coastal pelagic. We study how climate change could alter their three-dimensional spatial distribution, size structure, and trophic interactions by the end of the century. A set of sensitivity experiments further reveals the most influential environmental factors (e.g. primary production, temperature) driving these changes and how their importance may evolve over time. The results provide insights into the three-dimensional spatial structure of pelagic ecosystems, offering a clearer picture of their functioning and resilience in a changing climate. 

How to cite: Dalaut, L., Maury, O., Lengaigne, M., and Barrier, N.: Modelling the future of pelagic ecosystems in a changing climate, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-451, https://doi.org/10.5194/oos2025-451, 2025.

Surfing, sailing, aquatic marathons, and beach sprint rowing are widely practiced sports with passionate supporters across various regions. Ocean-based sports (OBS) events generate significant societal benefits, attract a variety of sponsors, and drive positive outcomes for the tourism industry. Alongside their substantial economic impact and the elevated prestige of these four Olympic sports, they all critically depend on the health and stability of marine ecosystems. Key factors such as wind direction, wave patterns, and water temperature are not merely environmental variables - they are fundamental to the performance and success of OBS athletes. For these practitioners, the ocean is not only a stage but also an indispensable tool. However, recent extreme weather events have validated climate projections, casting doubt on the stability of oceanic conditions and exposing the potential for devastating consequences. The future of these sports grows increasingly uncertain as ocean warming, coastal erosion, and rising sea levels threaten the conditions essential for their practice. This article adopts an interdisciplinary approach—bridging law and economics—to analyze these impacts, shedding light on the risks to OBS and offering recommendations for adaptation.

How to cite: Flores PhD, M., Lasmar, G., and Massimiliani, M.: Navigating Uncertainty: The Impact of Climate Change on Ocean-Based Sports and Pathways for Adaptation  , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-944, https://doi.org/10.5194/oos2025-944, 2025.

Increasing anthropogenic CO₂ emissions underscore the urgent need to advance our understanding of Earth's marine carbon cycle to more accurately predict future climate conditions. Climate change is driving rapid alterations in the marine carbonate system, notably resulting in declines in both pH and the saturation state of carbonate minerals like aragonite and calcite. Marine teleost fish, which are known to be part of the biological pump, also produce magnesium rich carbonate minerals (“ichthyocarbonate”) in their intestines which are excreted to the marine environment. Therefore, marine teleost fish serve as a critical link between the biological and carbonate pumps in the ocean. All~13,000 species of marine teleost fish species likely produce CaCO₃, and the group is estimated to be one of the largest CaCO₃ producers in the ocean. Even though fish are strong acid-base regulators, it has been shown that an increase in temperature and in partial pressure of CO₂ results in higher production rate of ichthyocarbonate. Because marine teleosts contribute to both the biological pump and the marine inorganic carbon cycle, understanding the physiological responses of fish to a changing ocean environment of ichthyocarbonate is pivotal to accurate predictions of ichthyocarbonate production in the face of climate change. Prior work suggests that ichthyocarbonates are unusual with regards to chemistry and morphology, both characteristics which affect their fate post excretion. The aim of this study was to understand how ichthyocarbonates change elementally and morphologically as they move through the 4 regions of the marine fish intestine – anterior, mid, posterior, and rectal segments and compare these results with complementary measurements conducted on excreted ichthyocarbonates.  We assessed the mol%MgCO₃ content, dissolution rate, organic matter content, and morphology of ichthyocarbonate from all 4 regions of the intestine and excreted ichthyocarbonates. We found that the mol%MgCO₃ is overall high, ranging from 74 to 56%, and decreases significantly as the ichthyocarbonate moves through the intestine, a trend opposite to previously documented Mg²⁺ concentrations in intestinal fluid. Also unexpectedly, the dissolution rate of ichthyocarbonate from the more distal regions was higher than anterior ichthyocarbonate, despite having lower mol%MgCO₃. Previous investigation of inorganic magnesium-rich carbonate minerals indicates that with increasing mol%MgCO_3, dissolution rate increases. However, mol%MgCO₃ is not an overarching control on dissolution rate of ichthyocarbonate, and increased organic matter content has been shown to strongly reduce dissolution rates, a plausible explanation for our observed relationship. To test this, organic matter content was assessed on ichthyocarbonate from all intestinal regions, and indeed, ichthyocarbonate collected from the rectal segments contained lower amounts of organic matter than ichthyocarbonate in more proximal segments, however it evaded significance. Finally, the morphology of ichthyocarbonate crystallites was heterogenous throughout all intestinal regions, but heterogeneity decreased as the ichthyocarbonate progressed through the regions of the intestine.

How to cite: Walls, S., Grosell, M., Oehlert, A., Marek, B., and Pope, C.: Ichthyocarbonates collected from the intestine differ in composition, morphology, and dissolution rate among regions and from post-excretion ichthyocarbonate, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1476, https://doi.org/10.5194/oos2025-1476, 2025.

On-going climate change is now recognized to yield physiological stresses on marine species, with potentially detrimental effects on ecosystems. Here, we  se metbaolic constraints to assess potential changes in suitable aerobic habitat in the South East Pacific. Our approach uses physiological traits (critical  xygen thresholds and metabolic indices) and climate velocities indicating the level of exposure to environmental changes simulated (CESM-LE) under a  RCP 8.5 scenario. The SEP is chosen as a case study as it hosts an Oxygen Minimum Zone and seamounts systems sustaining local communities through  artisanal fisheries relying on a number of endemic species. Our results reveal that changes in aerobic habitat are constrained by the oxygen distribution and by contrasting oxygen trends (including a re-oxygenation in the upper OMZ) and warming trends. Hence, while climate change highly impacts seamount systems, the OMZ ans its vicinity can be considered a “safe” area as it also experience the slowest changes. Contrasted latitudinal and vertical changes would likely result in altered trophic interactions. As the SEP also experiences the consequences of the El Nino Southern Oscillation (ENSO), we compare the impacts of climate change to ENSO events at the 2100 horizon.

How to cite: Parouffe, A., Paulmier, A., Garçon, V., and Dewitte, B.: Impact of climate change and ENSO on marine aerobic habitat in the South East Pacifc, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-509, https://doi.org/10.5194/oos2025-509, 2025.

Seagrass meadows play a crucial ecological role, with Nanozostera japonica being the most widely distributed seagrass species in China. However, it faces severe degradation. In the Yellow River Delta, Shandong, China, the largest N. japonica meadow once existed. Invasive Spartina alterniflora has encroached upon N. japonica habitats. UAV (unmanned aerial vehicle) tracking from 2015 to 2019 revealed a 516-fold increase in the distribution area of S. alterniflora within the study region. Between April and July 2019, it advanced 14 meters into seagrass areas, spreading long distances via seed dispersal and short distances through clonal growth. With increasing levels of S. alterniflora invasion, the growth of N. japonica was significantly suppressed. In early August 2019, Typhoon Lekima severely impacted the seagrass meadows in the Yellow River Delta, reducing their distribution area from 1,031.8 hectares to less than 10 hectares and decreasing the surface soil organic carbon (35 cm depth) by 35%. During the typhoon, N. japonica was in its flowering stage, and its sexual reproduction was severely affected, resulting in a significant reduction in seed production. Soil erosion caused by the typhoon led to massive seagrass mortality, drastically decreasing the density of overwintering shoots. As a result, natural recovery of the seagrass in this region is highly challenging, necessitating artificial restoration efforts to expedite meadow recovery.

How to cite: Yue, S., Zhou, Y., Zhang, X., Xu, S., and Zhang, Y.: The negative impacts of invasive species and extreme climate events on seagrass meadows and their soil organic carbon (SOC) pools, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-952, https://doi.org/10.5194/oos2025-952, 2025.

Coastal areas, experiencing rapid urbanization and population growth, are among the most dynamically changing regions on Earth. These zones face increasing risks from storms and rising sea levels, posing significant challenges for sustainable shoreline management. Traditional coastal monitoring, though accurate, is costly and time-consuming, often covering limited areas or requiring substantial processing time, which is impractical for authorities needing quick, actionable insights. Technologies like DGPS, UAV photogrammetry, and LIDAR have been employed, but they struggle to meet the frequency and scale needed for effective large-scale monitoring.

In response, the Space for Shore consortium, under the European Space Agency’s Coastal Erosion Project and led by i-Sea, leverages satellite imagery to offer an affordable and expansive solution. The project developed and deployed prototype monitoring tools along more than 5000 km of coastline, covering diverse European coastal environments. By using 25 years of data from the Copernicus program and other satellite missions, this approach captures and analyzes long-term erosion patterns and episodic erosion events across a range of coastal dynamics, from nearshore to inland regions.

Addressing the non-linear and regionally varied nature of coastal erosion, Space for Shore uses high-resolution optical and SAR satellite imagery to generate key indicators like waterlines, beach widths, dune positions, and seaward vegetation edges. This data is used to map changes with tailored temporal frequencies, from monthly to annual, to match local environmental rhythms, assessing both gradual erosion trends and immediate impacts from events like storms or fires. The study spans regions across France, Germany, Greece, Romania, Portugal, and Norway (including Svalbard Archipelago).

The key findings indicate significant coastal retreat across various locations. In the Danube Delta, up to 330 meters of shoreline have been lost over the past 30 years. France's Cotentin Coast has experienced rapid dune erosion following Storm Eleanor. Greece’s Evia Island has also suffered erosion after recent wildfires, while the Svalbard Archipelago shows marked glacier front retreat likely linked to climate change. Additionally, popular tourist destinations like Portugal’s coastline and Germany’s Sylt Island have seen shorelines recede by several tens of meters in recent years.

The project aims to provide an end-user-focused, validated set of tools and data for European coastal managers, ultimately supporting evidence-based planning and a multi-criteria classification of vulnerability to coastal erosion. The collaboration between remote sensing experts and over 60 stakeholders from government, academia, and industry emphasizes the initiative’s practical value in ongoing coastal management efforts.

How to cite: Pillet, V., Tranchand-Besset, M., Regniers, O., Kalousi, G., Constantin, S., Stelzer, K., Baptista, P., and Haarpaintner, J.: Advancing Coastal Monitoring: Satellite Solutions for Erosion and Shoreline Management Across Europe – The ESA Coastal Erosion Project, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1135, https://doi.org/10.5194/oos2025-1135, 2025.