T2-4 | Nature-based approaches for climate mitigation and adaptation

T2-4

Nature-based approaches for climate mitigation and adaptation

Orals

| Tue, 03 Jun, 14:00–15:30 (CEST)|Room 2

Posters on site

Posters virtual

Further information on the theme is available at: https://one-ocean-science-2025.org/programme/themes.html#T2

Orals: Tue, 3 Jun, 14:00–15:30 | Room 2

Chairperson: Helmuth Thomas

14:00–14:10

OOS2025-291

Redefining what we consider a ‘blue carbon ecosystem’

Nick Kamenos, Kelly James, Peter Macreadie, Heidi Burdett, and Ian Davies

Photoautotrophic marine ecosystems can lock up organic carbon in their biomass and the associated organic sediments they trap over millennia and are thus regarded as blue carbon ecosystems. Because of the ability of marine ecosystems to lock up organic carbon for millennia, blue carbon is receiving much attention within the United Nations’ 2030 Agenda for Sustainable Development as a natural climate solutions and possible nature-based solution, but classically still focuses on seagrass meadows, mangrove forests, and tidal marshes. However, other coastal ecosystems could also be important for blue carbon storage, but remain largely neglected in carbon cycling budgets. Using a meta-analysis of 253 research publications, we identify other coastal ecosystems – including mud flats, fjords, coralline algal (rhodolith) beds, and some coral reef systems – with a strong capacity to act as blue carbon sinks in certain situations. Features that promote blue carbon burial within these ‘non-classical’ blue carbon ecosystems included: (1) balancing of carbon release by calcification via carbon uptake at the individual and ecosystem levels; (2) high rates of allochthonous organic carbon supply because of high particle trapping capacity; (3) high rates of carbon preservation and low remineralisation rates; and (4) location in depositional environments. Some of these features are context-dependent, meaning that these ecosystems were blue carbon sinks in some locations, but not others. We provide a universal framework that can evaluate the likelihood of a given ecosystem to behave as a blue carbon sink for a given context. We seek to encourage consideration of non-classical blue carbon ecosystems within management strategies, allowing more complete blue carbon accounting.

How to cite: Kamenos, N., James, K., Macreadie, P., Burdett, H., and Davies, I.: Redefining what we consider a ‘blue carbon ecosystem’, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-291, https://doi.org/10.5194/oos2025-291, 2025.

14:10–14:20

OOS2025-751

Is blue carbon a ‘red herring’? Problems regarding magnitude, cost-effectiveness and timescale

Sophia Johannessen and Phillip Williamson

Avoiding the most catastrophic consequences of climate change will require some amount of carbon dioxide removal, in addition to urgently reducing emissions. Options for such removal include nature-based solutions, such as “blue carbon” burial in the sediment of vegetated coastal ecosystems (mangroves, salt marshes and seagrass meadows). Very high carbon sequestration rates have been claimed for these blue carbon ecosystems, and many media outlets have uncritically endorsed this message. Unfortunately, there seems to be some over-optimism among researchers, the general public and policy-makers, about the actual climate mitigation potential of coastal blue carbon.

We identify three main reasons why blue carbon ecosystems are unsuitable for directly offsetting fossil fuel emissions. First, the magnitude of the any climate benefit is likely to be much smaller than claimed, due to a range of methodological issues; second, the cost-effectiveness is low, particularly in developed countries; and third, there is a mismatch in timescale between the emission of ancient fossil carbon and the storage of carbon by vegetated ecosystems. Given these limitations, we suggest that blue carbon may be a misleading distraction (i.e. a ‘red herring’) for climate mitigation purposes. Nevertheless, blue carbon ecosystems provide many benefits. Protection of such habitats and their restoration, where practicable, would protect critical habitat for diverse species, prevent coastal erosion, reduce storm damage, promote food security and provide opportunities for tourism.

How to cite: Johannessen, S. and Williamson, P.: Is blue carbon a ‘red herring’? Problems regarding magnitude, cost-effectiveness and timescale, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-751, https://doi.org/10.5194/oos2025-751, 2025.

14:20–14:30

OOS2025-993

ECOP

Ocean acidification enhances carbon burial in seagrass meadows: new insights from CO2 vents

Theodor Kindeberg, Núria Teixidó, Steeve Comeau, Jean-Pierre Gattuso, Beat Gasser, Alice Mirasole, Samir Alliouane, Ioannis Kalaitzakis, and Pere Masque

Seagrass meadows of Posidonia oceanica are well known natural carbon sinks, burying large amounts of organic carbon (C_org) in their underlying sediments. However, it is not well understood how C_org burial will be affected by ocean acidification (OA). While the primary production of P. oceanica is anticipated to benefit from a lower pH, it is unknown how C_org burial rates respond as these are influenced by additional abiotic and biotic factors that may interact with OA in various ways.

Here, we utilize natural CO₂ vents as OA analogs to evaluate C_org burial rates as a function of water column pH. We sampled 14 sediment cores across three different sites around the island of Ischia, Italy, comprising pH regimes from ambient (pH_T≈8.0) to low pH_T (7.5-7.8) and extreme low pH_T (6.6-7.2). We used concentration profiles of ²¹⁰Pb and C_org to estimate C_org burial rates of the past ~100 years. We concomitantly assessed signatures of stable isotopes 𝛿¹³C and 𝛿¹⁵N along the depth profiles to estimate the contribution from different primary producers to sediment C_org.

We found low C_org burial rates at ambient pH but rates became markedly elevated as a function of lowered pH, with extreme low pH sites displaying nearly an order of magnitude higher rates compared to ambient pH sites. Moreover, sediment cores collected within CO₂ vents revealed an increasing C_org burial rate over the last 30 years, whereas those outside of vent areas displayed a stable or decreasing pattern with time. We hypothesize that this reflects an increase in volcanic activity that has spurred elevated CO₂ release rates in recent decades, thus further decreasing seawater pH. Our findings suggest that seagrass meadows may represent a negative feedback between OA and C_org burial, with possible ramifications for their future climate change mitigation potential. We will discuss the potential mechanisms behind these findings.

How to cite: Kindeberg, T., Teixidó, N., Comeau, S., Gattuso, J.-P., Gasser, B., Mirasole, A., Alliouane, S., Kalaitzakis, I., and Masque, P.: Ocean acidification enhances carbon burial in seagrass meadows: new insights from CO2 vents, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-993, https://doi.org/10.5194/oos2025-993, 2025.

14:30–14:40

OOS2025-851

Quantifying Carbon Sequestration in Restored Seagrass Meadows for Climate Mitigation

Elisabeth Sellinger, Melissa Ward, Tessa Hill, Mazie Lewis, Xinyu Wang, Lauren Duncan, and Lucille Bates

Seagrasses, vital marine flowering plants, cover less than 0.2% of the ocean floor yet play a crucial role in carbon sequestration, contributing up to 18% of annual ocean carbon burial. Their decline due to human impacts, such as rising temperatures, nutrient runoff, and invasive species, threatens this ecosystem service, with California losing approximately 35% of its seagrass cover since 1980. This research aims to address critical knowledge gaps regarding the carbon storage capacity and sediment dynamics in restored versus natural seagrass meadows, focusing on their effectiveness as a nature-based approach to meet the mitigation goals outlined in the Paris Climate Agreement. The study is centered on three primary objectives, developed in collaboration with two U.S. National Marine Sanctuaries, and focuses on California’s dominant seagrass species, Zostera marina (eelgrass): 1) assessing short-term sediment accumulation and erosion rates before and after restoration; 2) comparing carbon stocks in recently restored meadows with those in natural meadows; and 3) investigating the contributions of allochthonous carbon from adjacent ecosystems. We hypothesize that restoration efforts will enhance sedimentation rates relative to control unvegetated sites, and that restored meadows will initially sequester carbon at lower rates than natural meadows, eventually achieving parity within 2–3 years. To achieve these objectives, we have employed field experiments and laboratory analyses. Specifically, 24 subsurface sediment plates were installed in Central California to monitor sediment changes, and sediment cores were collected to analyze total organic matter and grain size. Stable isotope analyses will help differentiate mixed sources of carbon, providing insights into contributions from seagrass, salt marshes, and terrestrial inputs—a critical science need identified by carbon credit methodologies and greenhouse gas inventories. Preliminary results show short-term accumulation of sediments composed of approximately 7.72% total organic matter. By elucidating the carbon dynamics associated with seagrass restoration, this research contributes to understanding the potential of nature-based solutions in climate mitigation and adaptation. It also emphasizes the importance of community engagement in formulating research questions, ensuring that the work addresses the needs of local stakeholders. Ultimately, our findings will inform strategies for enhancing the resilience of coastal ecosystems and communities in the face of ongoing climate change.

How to cite: Sellinger, E., Ward, M., Hill, T., Lewis, M., Wang, X., Duncan, L., and Bates, L.: Quantifying Carbon Sequestration in Restored Seagrass Meadows for Climate Mitigation, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-851, https://doi.org/10.5194/oos2025-851, 2025.

14:40–14:50

OOS2025-1319

Fixing the Arctic? The Unintended Consequences of Geoengineering Proposals

Odile Crabeck and the Biogeochemical Exchanges Processes at Sea Ice Interfaces (BEPSII working group)

As global climate warming intensifies, various geoengineering strategies have been proposed to restore Arctic sea ice. Two prominent approaches—seawater flooding in winter to thicken sea ice and spreading artificial snow made of reflective glass microspheres—have gained attention for their potential to enhance surface albedo and slow sea-ice melt.

However, the effectiveness of these interventions is increasingly questioned, with recent studies highlighting possible unintended consequences. Both techniques are predicted to alter light transmission and gas fluxes, and disrupt algal phenology, potentially leading to mismatches in zooplankton feeding and affecting the broader Arctic food web. Additionally, the silica content in glass beads has the potential for fertilization effects on marine algal blooms, favouring diatoms and disrupting natural algal succession.

Given the large-scale infrastructure and invasive nature of these methods, there is an urgent need for comprehensive numerical studies to assess their long-term impacts on Arctic biogeochemistry and ecosystems. Even small-scale field tests should be approached cautiously and should include rigorous biogeochemical studies to evaluate unintended consequences on local and larger scales. In addition to environmental impacts, these strategies raise significant ethical, legal, and political challenges that must also be considered.

This abstract is submitted by Biogeochemical Exchanges Processes at Sea Ice Interfaces (BEPSII working group)

https://sites.google.com/site/bepsiiwg140/home

How to cite: Crabeck, O. and the Biogeochemical Exchanges Processes at Sea Ice Interfaces (BEPSII working group): Fixing the Arctic? The Unintended Consequences of Geoengineering Proposals, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1319, https://doi.org/10.5194/oos2025-1319, 2025.

14:50–15:00

OOS2025-103

Opportunities and risks to climate mitigation using seabed carbon stores: insights from the Convex Seascape Survey

Callum Roberts

Limiting global warming to below 2^oC will require the use of nature-based solutions for carbon capture at vast scales. With terrestrial vegetation carbon sinks faltering due to the impacts of heat, drought and wildfire, interest in marine carbon sinks is growing. The seabed represents an enormous carbon sink due to the burial of organic matter in ocean sediments, especially fine-grained muds. These carbon stores, built over thousands of years, are not impregnable, however, being at risk of remobilisation and remineralisation into CO₂ by industrial activities. For over 200 years, the seabed of coastal continental shelves has become increasingly disturbed by bottom fishing using trawls and dredges, channel excavation for ports and harbours, aggregate extraction, cable laying, offshore oil, gas and wind energy. Scientific research indicates that these activities release stored organic carbon, creating emissions to the ocean and atmosphere. But determining their magnitude is complex and results obtained to date are therefore highly controversial. Resolving this debate requires new, highly multidisciplinary science. The Convex Seascape Survey is a five-year global programme of over 20 institutions and more than 120 experts dedicated to understanding the seabed carbon of continental shelves, quantifying the risks it faces from human activities, and publishing open access data to maximise the reach and value of the insights gained. This presentation will describe how the project is combining expertise from multiple fields to generate detailed maps of ocean carbon distribution, identify the origins of these deposits, and quantify how they have been altered by centuries of human industrial use. The talk will showcase important new data on the risks seabed carbon stores face and how protective management can recover critical ecological processes that promote carbon capture and burial. It is becoming apparent that some of the most important and vulnerable places from a carbon storage perspective support economically important intensive fisheries. Such areas have also been neglected in the process of building marine protected area networks, because soft sediments have erroneously been considered of low biodiversity value and robust to human impacts. Managing ocean carbon stores to mitigate climate change is going to require an urgent rethink of management and protection priorities continental shelves.

How to cite: Roberts, C.: Opportunities and risks to climate mitigation using seabed carbon stores: insights from the Convex Seascape Survey, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-103, https://doi.org/10.5194/oos2025-103, 2025.

15:00–15:10

OOS2025-26

ECOP

Natural climate solutions based on fish, fisheries, and marine mammals: Current evidence and assessment of readiness

Jamie Collins, Mattias Cape, Robert Boenish, Claudia Benitez-Nelson, Scott Doney, Rod Fujita, Steven Gaines, Rebecca Gruby, Di Jin, Heather Kim, Kristin Kleisner, Gaël Mariani, Lisa Moore, Andrew Pershing, Douglas Rader, Joe Roman, Grace Saba, James Sanchirico, Steven Saul, and Matthew Savoca

Several initiatives to conserve, restore or better manage fisheries, fishes, whales, and other marine mammals have been proposed as natural climate solutions to sequester carbon from the atmosphere or avoid new emissions. We reviewed the knowledge and uncertainties surrounding carbon fluxes and storage mediated by these organisms to evaluate their suitability to support climate mitigation interventions. Estimates of the carbon stored within fish and marine mammal biomass ranged from 0.1-1.9 Pg C for mesopelagic fishes, 0.0020-0.016 Pg C for great whales, and 0.0065-0.0113 Pg C for all marine mammals, compared to an estimated 1.5-3 Pg C stored in all ocean biota. Epipelagic fishes, mesopelagic fishes, and great whales contribute on the order of 0.03-0.2 Pg C yr^-1, 1-3 Pg C yr^-1, and 0.001-0.004 Pg C yr^-1, respectively, to carbon export from the ocean’s surface to below the euphotic zone, compared to an estimated total marine biological export of 9-10 Pg C yr^-1. The combined flux of carbon to the atmosphere from benthic trawling, biomass extraction, and fuel consumption during commercial fishing ranged from 0.05-0.25 Pg C yr^-1. Substantial uncertainties were associated with nearly all fluxes and reservoirs. The contributions of whales to carbon export and the mobilization of carbon from sediments during benthic trawling were least certain, limiting the readiness of associated pathways to provide quantifiable, high-quality carbon credits. While substantial uncertainties also surrounded mesopelagic fishes, we found that even the most conservative estimates of these organisms’ contribution to ocean carbon export were large enough to justify precautionary conservation actions.

How to cite: Collins, J., Cape, M., Boenish, R., Benitez-Nelson, C., Doney, S., Fujita, R., Gaines, S., Gruby, R., Jin, D., Kim, H., Kleisner, K., Mariani, G., Moore, L., Pershing, A., Rader, D., Roman, J., Saba, G., Sanchirico, J., Saul, S., and Savoca, M.: Natural climate solutions based on fish, fisheries, and marine mammals: Current evidence and assessment of readiness, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-26, https://doi.org/10.5194/oos2025-26, 2025.

15:10–15:30

Discussion

Posters on site | Poster area "La Baleine"

Display time: Tue, 3 Jun, 17:00–Thu, 5 Jun, 20:00

P113

OOS2025-66

ECOP

West Africa Ocean Climate Innovations Hub

Peter Teye Busumprah

This Oral Presentation is to address UN Ocean Decade Challenges 5 & 6 to unlock ocean based solutions to climate change , and community resilience

It focuses on SDGs 9, 13 & 14 which is centred on industry , innovation and infrastructure, Climate change and life below water.

The oral presentation is Ocean Visions - Ocean Rock Base Hub aims to fill a crucial gap in the Ocean Decade by focusing on nature and ocean-based solutions for climate remediation in West Africa, with a specific emphasis on Ghana. This initiative seeks to identify and collaborate with relevant stakeholders from diverse backgrounds, including scientists, corporate executives, government agencies, civil society groups, NGOs, academia, and community organisations actively involved in nature-based solutions (NBS) activities in Africa. By bringing together these stakeholders, the project will establish a dedicated task force that can effectively implement NBS strategies in the region. This aligns with the current call for decade actions as it addresses the urgent need for climate remediation and recognizes the significance of harnessing the potential of the ocean and nature-based approaches. The proposed actions will contribute to the overall goals of the Ocean Decade by promoting sustainable and inclusive solutions that protect and restore the ocean and its ecosystems while addressing climate challenges in West Africa.

The Ocean Innovation Hub has the potential to bring a multitude of benefits to the West Africa region. These benefits include economic growth through job creation and innovation, improved resilience to climate change impacts, enhanced knowledge sharing and research collaboration, and the preservation of vital marine and coastal ecosystems. It's not just about addressing climate change; it's also about creating a more sustainable and prosperous future for the people and ecosystems of West Africa. By working together on this initiative, West Africa can make significant strides toward achieving its climate and sustainability goals. It can become a leader in the development and implementation of nature-based solutions, setting an example for other regions facing similar challenges. This, in turn, can improve the quality of life for its residents, protect coastal communities from the ravages of climate change, and help preserve the region's rich biodiversity.

How to cite: Busumprah, P. T.: West Africa Ocean Climate Innovations Hub, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-66, https://doi.org/10.5194/oos2025-66, 2025.

P114

OOS2025-342

Promoting carbon-neutral snorkeling tourism in the coral reefs at Mu Ko Tao, Gulf of Thailand to achieve Net-Zero Tourism

Thamasak Yeemin, Makamas Sutthacheep, Sittiporn Pengsakun, Wanlaya Klinthong, Charernmee Chamchoy, and Phatthira Karnpakob

Tourism is one of the largest industries globally, contributing significantly to greenhouse gas (GHG) emissions. Within the tourism industry, marine tourism is a rapidly expanding segment. Tourism-related activities significantly contribute to global carbon dioxide emissions, accounting for approximately 8% of total worldwide emissions. Thailand's marine tourism industry is one of the most popular and widely attended tourism activities worldwide, attracting tourists worldwide. This study aims to assess the impact of a snorkeling route, Ko Nang Yuan and Ao Muang for a one-day trip at Mu Ko Tao, Surat Thani Province, in the Western Gulf of Thailand, which is recognized as one of Thailand's most popular snorkeling destinations. We use the Life Cycle Assessment method (LCA), focused on the Carbon Footprint (CF) impact category, to assess the carbon dioxide emissions associated with transportation, accommodation, food and beverages, and waste management. The results showed that the carbon dioxide emission associated with the snorkeling route was approximately 7.89 kg CO2 eq./person. Of this total, transportation accounted for nearly 69.8%, food consumption contributed 28.8%, and waste management practices made up 1.4%. Transport by wooden boats with diesel engines resulted in the highest carbon dioxide emissions; therefore, alternatives were proposed to reduce these impacts by transitioning to electric, hybrid, or more fuel-efficient boats. In terms of food consumption, it would be ideal to prioritize purchasing food from local farmers and fishers. This would help reduce transportation emissions associated with food delivery. Additionally, it is encouraged to utilize seasonal fruits, vegetables, and seafood, as these items require less energy for production and transportation. For carbon offsetting, the ZERO CARBON application has been designed as a tool for accurately quantifying and offsetting carbon emissions produced by tourism operations. By utilizing advanced emission-tracking methodologies, the platform enables operators to counterbalance their carbon footprint through scientifically vetted environmental projects, such as afforestation, reforestation, and renewable energy systems, thereby contributing to measurable reductions in atmospheric carbon dioxide levels. Finally, the findings are critically analyzed, and a series of mitigation strategies for reducing greenhouse gas emissions are proposed. These strategies focus on implementing sustainable practices and the establishment of rigorous environmental commitments among marine tourism providers, stakeholders, and local communities. The proposed measures aim to systematically reduce emissions and support the transition towards achieving Net Zero Tourism.

How to cite: Yeemin, T., Sutthacheep, M., Pengsakun, S., Klinthong, W., Chamchoy, C., and Karnpakob, P.: Promoting carbon-neutral snorkeling tourism in the coral reefs at Mu Ko Tao, Gulf of Thailand to achieve Net-Zero Tourism, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-342, https://doi.org/10.5194/oos2025-342, 2025.

P115

OOS2025-359

Nature-Based Solutions: Enhancing Coastal and Marine Conservation in the Western Indian Ocean in Africa

Denise Nicolau and the Denise Nicolau

The Western Indian Ocean (WIO) hosts some of the world’s most extensive and climate-resilient mangroves, seagrass and coral reefs. These ecosystems are crucial sources of food, coastal protection, and income for coastal populations. These assets are conservatively valued at US$333 billion and provide at least US$21 billion annually to the regional economy through tourism, carbon sequestration, and fisheries.

Nevertheless, real and significant threats such as overexploitation of fisheries, habitat clearing, and pollution are jeopardizing the integrity of the region’s marine ecosystems and their ability to provide goods and services to coastal communities. These threats are exacerbated by climate change impacts including sea-level rise, changes in sea temperature, ocean acidification, and storm events.

Therefore, it is critical to support resilient and productive ecosystems and the concept of Nature based solutions (NbS) to support coastal and marine conservation in the WIO region aims to provide insightful perspectives from global and local experiences across interconnected regenerative seascapes in Comoros, Kenya, Madagascar, Mozambique, and Tanzania, where NbS serves to guide actions to protect, sustainably manage and restore coastal and marine ecosystems, enhancing livelihoods of local communities, while contributing for the 2030 agenda.

How to cite: Nicolau, D. and the Denise Nicolau: Nature-Based Solutions: Enhancing Coastal and Marine Conservation in the Western Indian Ocean in Africa, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-359, https://doi.org/10.5194/oos2025-359, 2025.

P117

OOS2025-499

Vida Manglar, blue carbon program in the Colombian Caribbean

Maria Claudia Diazgranados, Yoger Yair Madarriaga, Paula Ortega, Yenis Simanca, Dalila Caicedo, Yenyfer Mona, Paula Sierra, Amy Schmid, and Jennifer Howard

The Blue Carbon Project, Gulf of Morrosquillo "Vida Manglar", is a local institutional and regional community initiative, which seeks certification of actions related to the reduction of carbon emissions due to unplanned deforestation and the conservation of coastal wetlands in 7,561 ha of mangrove forests. The grouped project began on May 15, 2015, and is expected to last 30 years. During that time a reduction of 939,296 tCO2e is expected through the implementation of activities related to four strategic lines framed in the Action Plan of the Integrated Management Plan of the protected area of Cispatá: strengthening local governance; promoting alternative productive projects with local communities; recovery and rehabilitation of mangrove areas; and monitoring the associated biodiversity. During the first monitoring period (15 May 2015 to 31 December 2018) a net reduction of 69,027 tCO2e was certified. The program is developing the second monitoring report.

Vida Manglar is led by a coalition of public and private organizations — including the national environmental authorities Coporación Autónoma Regional del Valle del Sinú (CVS), the Colombia’s Marine and Coastal Research Institute (INVEMAR), the local NGO Fundación Omacha, Conservation International and community-based associations of mangrove workers. Communities living around the project area have a high economic dependence on the natural resources associated with the mangrove forests. Historically, they have promoted different sustainable management initiatives together with the authority to improve their economic welfare and to maintain the environmental quality of the ecosystem. They are part of the governance structure of the project and a key partner for decision-making processes. One unique characteristic of this project is the existence of a rotating forest management scheme that allows local communities to use mangrove wood based on permits granted by the regional environmental authority on a yearly basis.

In Colombia the use of mangrove wood is prohibited for any purposes, but in Cordoba Department, due to an extensive mangrove monitoring done with communities since 1990, the authority reached to the conclusion that using sustainably the mangrove forest was a better way of keeping them healthy, instead of prohibiting the use that might create illegal activities. That is why mangrove users are associated and receive extraction permits every year, based on volume of wood collected and monitored by the authority. The entire mangrove forest is divided into 13 different subzones, which are harvested by year on a rotation basis. In exchange for making specific commitments that limit the amount of wood they extract from the mangrove forest, as well as the active participation on monitoring activities, community members receive benefits from the blue carbon program, such as wages for opening channels to avoid high salinity levels, capacity building opportunities, as well as economic alternatives. The local knowledge is used to select which channels needs an urgent maintenance, as well as how is the best way of helping and increasing the natural regeneration of the forest.

How to cite: Diazgranados, M. C., Madarriaga, Y. Y., Ortega, P., Simanca, Y., Caicedo, D., Mona, Y., Sierra, P., Schmid, A., and Howard, J.: Vida Manglar, blue carbon program in the Colombian Caribbean , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-499, https://doi.org/10.5194/oos2025-499, 2025.

P118

OOS2025-885

Engineering Resilience: The Noosa Oyster Ecosystem Restoration Project as a Model for Nature-Based Coastal Adaptation

Sam King, Aaron Salyer, Angus Jackson, Bobbie Corbett, and Craig Bohm

Shellfish reefs are an essential ecology for the health, resilience and sustainability of estuarine and marine ecosystems throughout the world. They create complex habitats, filter large volumes of water, enhance fish productivity and sequester carbon dioxide. However, from the 19th century, many shellfish habitats were severely damaged or destroyed and their preservation and restoration is now a priority. More recently, their capacity to mitigate erosion, sequester carbon dioxide and build wider foreshores has resulted in their adoption as a nature-based solution for coastal protection.

The Noosa Oyster Ecosystem Restoration Project is one such project that highlights the value of engineering innovation in nature-based coastal resilience and the effectiveness of shellfish reefs as engineered infrastructure. The project was led by The Nature Conservancy (TNC) in partnership with The Thomas Foundation, Noosa Shire Council and the Australian Government Reefbuilder program, with the aim of restoring oyster reefs and their benefits to the lower Noosa River. Stakeholder consultation with local community groups and Traditional Owners aligned the project to their values and priorities, setting a model for equitable adaption in coastal communities. A multidisciplinary planning approach was also adopted to ensure compliance with regulatory standards.

International Coastal Management (ICM) worked with TNC to facilitate approvals and lead the engineering and construction of the project. ICM applied advanced coastal engineering and adaptive design methods to create 30 reef patches covering 2,268 m², selected through rigorous site analysis and environmental mapping. The challenges of the estuarine site required innovative reef designs strategically positioned to promote oyster recruitment, stabilise the riverbank, and accommodate the river’s steep profile, ensuring navigational safety and minimising impacts on sensitive habitats and local processes. The reefs were constructed with locally sourced igneous rock, precisely placed with barge-mounted excavators and with spat seeded oyster shells placed within voids. This design optimised conditions for oyster colonisation and habitat complexity to enhance the estuarine ecosystem.

Following the completion of the reefs in October 2022, monitoring documented successful young oyster ‘spat’ recruitment, high oyster densities, and growth rates exceeding targets, with 550 oysters per m² compared to a baseline goal of 200 per m². Mangrove and seagrass colonisation at the reefs and stabilisation of the riverbank was also observed. Throughout 2023-2024, monitoring revealed the engineered reefs outperformed natural oyster beds which had degraded in that time. This design approach positioned ICM’s engineering work as a technical benchmark for shellfish reef restoration, providing a resilient and adaptable coastal defence structure within a complex estuarine system.

The Noosa Oyster Ecosystem Restoration Project demonstrates how engineering can create adaptable, nature-based solutions to coastal challenges. By integrating robust technical design with ecological goals and community priorities, ICM developed a scalable, effective model for global coastal resilience aligned with the Paris Climate Agreement. This project serves as a case study on how science-driven, multidisciplinary engineering can enhance the resilience of estuarine ecosystems and address the evolving demands of climate adaptation.

How to cite: King, S., Salyer, A., Jackson, A., Corbett, B., and Bohm, C.: Engineering Resilience: The Noosa Oyster Ecosystem Restoration Project as a Model for Nature-Based Coastal Adaptation, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-885, https://doi.org/10.5194/oos2025-885, 2025.

P119

OOS2025-954

ECOP

Contributions of Sulfur, Iron, and Carbon Biogeochemistry to Alkalinity Production in a Northern California Zostera marina Meadow

Liyu Mekonnen, Manuel Delgado, Mazie Lewis, Elizabeth Miller, Brendan Tang, and Alyssa Griffin

Vegetated coastal marine systems, also known as blue carbon ecosystems, are traditionally recognized for carbon capture and long-term storage both within their biomass and via organic carbon accumulation in their underlying sediments. Recently, alkalinity generation within the sediments of blue carbon ecosystems, such as seagrasses, has been proposed as an additional long-term sink for atmospheric carbon dioxide. Seagrasses can capture and provide the organic matter required to fuel biogeochemical processes that increase alkalinity in underlying sediments, such as bacterial sulfate reduction (BSR). BSR produces alkalinity by reducing sulfate in seawater to sulfide (e.g., H₂S). This sulfide can then react with iron to form the mineral pyrite (FeS₂) which, once buried, prevents sulfide reoxidation and frees the alkalinity produced to buffer overlying waters. Although seagrasses and pyrite formation are each well studied, there is still much to uncover about how they are related, how their interrelation impacts alkalinity production, and how that varies across a seagrass meadow. This study evaluates the intra-meadow variability of iron, sulfur, and carbon pools in a northern California Zostera marina meadow to better understand how sediment and seagrass characteristics influence alkalinity production at a higher spatial resolution. Initial results indicate significant organic matter variability across this seagrass meadow. Since BSR and subsequent pyrite formation are in part limited by organic matter availability, this variability suggests that alkalinity generation is also likely to be largely heterogeneous across a single seagrass meadow.

In addition to helping resolve gaps in local and global alkalinity budgets, this study also has implications for proposed marine carbon dioxide removal (mCDR) technologies. Deepening our understanding of alkalinity and carbon cycling in coastal environments, such as seagrasses, is imperative to assess the efficacy of many proposed mCDR interventions which served as additional motivation for this study.

How to cite: Mekonnen, L., Delgado, M., Lewis, M., Miller, E., Tang, B., and Griffin, A.: Contributions of Sulfur, Iron, and Carbon Biogeochemistry to Alkalinity Production in a Northern California Zostera marina Meadow, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-954, https://doi.org/10.5194/oos2025-954, 2025.

P122

OOS2025-1178

Mangrove-inspired approach as an alternative to traditional coastal infrastructure to tackle erosion issues

Julien Dalle, Mathis Cognat, Alice Gavoille, Marie Martinot, Paul Girardot, Maria Maza, and Alexis Beudin

Coastal erosion is a growing concern for many regions, threatening infrastructure, ecosystems, and local communities. Conventional hard-engineering solutions often lead to negative environmental impacts and disrupt natural coastal dynamics, while retreat and adaptation strategies can sometimes be challenging to implement. In response, we have been developing an innovative, nature-based approach inspired by the wave and current dissipating capabilities of mangrove ecosystems.

Mangroves, with their dense root systems, act as effective natural barriers, reducing wave energy, stabilizing sediments, and enhancing coastal resilience. Our project aims to replicate these benefits through a bio-inspired structure designed to mimic the intricate root networks of mangroves. This system uses strategically placed vertical and horizontal elements to dissipate wave energy and enhance sediment deposition, providing a sustainable method to control coastal erosion.

The design and implementation of this solution resulted from a collaborative effort among coastal engineers, ecologists, and numerical modelers. Advanced hydrodynamic simulations were conducted to assess and optimize the wave dissipation performance of the structure. A pilot installation at Grau d'Agde beach, a vulnerable site on the French Mediterranean coast, has provided promising initial results. Early monitoring data show significant reductions in wave energy and increased sediment retention, with promising ecological trends, indicating this nature-based approach can enhance coastal stability without compromising the local ecosystem.

This presentation will cover the design process, modelling results, and preliminary field data from the pilot project, illustrating the potential of bio-inspired solutions for addressing coastal erosion and providing insights for broader application in similar vulnerable coastal areas.

Keywords: Coastal Erosion, Nature-Based Solutions, Mangrove-Inspired Design, Wave Dissipation, Pilot Project, Field Monitoring, uUpscalling, Hydrodynamic Modeling.

How to cite: Dalle, J., Cognat, M., Gavoille, A., Martinot, M., Girardot, P., Maza, M., and Beudin, A.: Mangrove-inspired approach as an alternative to traditional coastal infrastructure to tackle erosion issues , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1178, https://doi.org/10.5194/oos2025-1178, 2025.

P123

OOS2025-1324

MaCoBioS Blue NbS Toolbox

Cindy Cornet, Rémy Simide, Bethan O'Leary, Gema Casal, Elisa Furlan, Vuong Pham, Elena Allegri, Christian Simeoni, Angelica Bianconi, Silvia de Juan, Emily Boyd, Géraldine Pérez, Jean-Philippe Maréchal, and Ewan Trégarot

Our societies are actively seeking solutions to address the crises of biodiversity loss and climate change. In this context, the European Horizon 2020 project MaCoBioS (2020-2024) supports effective and integrated management and conservation strategies for marine and coastal ecosystems to face climate change. Our goals were: to better understand the inter-relations between climate change, biodiversity, functions and services in marine and coastal ecosystems; to assess the vulnerability of marine and coastal socio-ecological systems under climate change scenarios; to evaluate the effectiveness of Nature-based Solutions (NbS) at enhancing the resilience capacity of ecosystems and societies; and to provide evidence-based guidance for policy formulation and innovative research pathways. The project outputs aim to increase the uptake of and investment in marine and coastal NbS that benefit both biodiversity and climate adaptation and mitigation, while ultimately improving human health and well-being, in line with the UN SDGs 3, 13 and 14. Implementation of Nature-based Solutions in marine and coastal environments (blue NbS) is slow. Reasons vary but include a lack of supportive tools for practitioners. The MaCoBioS Blue NbS Toolbox (https://macobios.eu/toolbox/) is a collection of multidisciplinary tools and products to facilitate the design and implementation of NbS. This Toolbox addresses critical questions: What happens to the ecosystem and its services under different scenarios? Why and where is managing local pressures essential given future ecosystem distributions under climate change? Where can we find the most favourable conditions for intervention? How can potential interventions (protection, restoration and other management measures) be applied within a local specific socio-environmental context? This presentation offers a synthesis of the main outputs of the MaCoBioS project and an introduction to its Toolbox.

How to cite: Cornet, C., Simide, R., O'Leary, B., Casal, G., Furlan, E., Pham, V., Allegri, E., Simeoni, C., Bianconi, A., de Juan, S., Boyd, E., Pérez, G., Maréchal, J.-P., and Trégarot, E.: MaCoBioS Blue NbS Toolbox, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1324, https://doi.org/10.5194/oos2025-1324, 2025.

P124

OOS2025-1351

ECOP

Toward the inclusion of oceanic conservation measures in the Nature-based Climate Solution portfolio

Gaël Mariani, Jérôme Guiet, Daniele Bianchi, Tim DeVries, Anaëlle Durfort, Nicolas Barrier, Mikaela Gomez, Niels Krabbe, Fabio Berzaghi, Mary Wisz, Marc Troussellier, and David Mouillot

It is clear now that Nature-based Climate Solutions (NbCS) – solutions designed to protect, restore, and sustainably manage ecosystems to mitigate climate change – are needed to achieve the net-zero climate targets. In a context where NbCS over-rely on land ecosystems, it is necessary to seek natural analogs in the ocean by focusing on components that contribute to oceanic carbon sequestration and that we can target through conservation measures, such as fish and the seabed.
Here, we estimate the past and future influence of fisheries on the carbon cycle by assessing their impact on the carbon sequestration potential of fish, as well as their contribution to greenhouse gas emissions, with the ultimate goal of discussing their potential inclusion in the NbCS portfolio.
We show that before the development of the fishing industry, fish of commercial interest induced a carbon export flux of 0.22 GtC.yr^-1 (eq. to 0.80 GtCO₂.yr^-1), and that exploitation has reduced export to 0.10 GtC.yr^-1(eq. to 0.36 GtCO₂.yr^-1). This means that the restoration of macrofauna populations towards their historical levels has a climate change mitigation potential of 0.124 GtC.yr^-1 (eq. to 0.45 GtCO₂.yr^-1), an estimate of the same order of magnitude as the one of mangroves restoration measures. Yet, as the vast ocean also plays a pivotal role in addressing socio-economic goals such as fisheries or food security, protecting oceanic areas for climate action should not impede these socio-economic goals. Consequently, finding areas where these potential conflicts are minimized is necessary to better inform the spatial management of fisheries. Regarding epipelagic fisheries, we find that most of the opportunities to safeguard and increase fish carbon sequestration lie in the high seas. Regarding bottom-trawling fisheries, the Arctic Ocean emerged as an area of major interest. Indeed, in a context where the Arctic would be sea-ice-free by the 2030s, these new open areas where the sediment carbon is still intact would soon become new bottom-trawling fishing grounds. We show that avoiding the development of these fisheries will avoid the emission of greenhouse gas emissions from fossil fuel burning and seabed carbon disturbance, without imperilling existing bottom-trawling fisheries. Our results therefore suggest that oceanic conservation measures are options to be considered for expanding the NbCS portfolio.

How to cite: Mariani, G., Guiet, J., Bianchi, D., DeVries, T., Durfort, A., Barrier, N., Gomez, M., Krabbe, N., Berzaghi, F., Wisz, M., Troussellier, M., and Mouillot, D.: Toward the inclusion of oceanic conservation measures in the Nature-based Climate Solution portfolio, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1351, https://doi.org/10.5194/oos2025-1351, 2025.

P125

OOS2025-1417

Climate change resilience and South Africa's estuarine associated fish species

(withdrawn)

Nicola James, Carla Edworthy, Lara van Niekerk, Stephen Lamberth, and Shaun Deyzel

P126

OOS2025-1421

ECOP

Land-sea continuum: long-term fate of terrestrial organic carbon in coastal environments of the Baltic Sea

Alexandra Rouillard, Cristian Gudasz, Jenny Ask, Siv Huseby, Luis Gonzalez Guerrero, Jan Karlsson, and Nicholas A. Kamenos

Natural climate solutions to climate change are recognised as a mechanism for drawing down carbon from the atmosphere. Together with geoengineering, this represents a potential solution for reducing anthropogenic carbon dioxide (CO₂) concentrations in the atmosphere, which are contributing to global warming. The storage of carbon in marine sediments at the land-sea interface of the continental shelves is a globally significant process. These sediments play a crucial role by providing both sequestration and efficient carbon burial, enabling marine systems to serve as effective natural climate solutions. For the subarctic, there is emerging evidence that at millennial time scales, approximately 50% of organic carbon (OC) buried in shallow-water marine sediments may be organic material derived from terrestrial and inland water systems via riverine discharge. In the Baltic Sea, these processes have mostly been investigated in the deeper basins, and with limited data available on the origins of this stored carbon through time. Furthermore, evidence suggests that multiple anthropogenic influences affecting e.g., the riverine delivery of OC and nutrients and the physical integrity or redox status of sediments could lead to altered storage capacity of the system, including rapid remineralisation of old organic carbon into greenhouse gas. To determine the location of Baltic organic carbon storage hotspots and their sensitivity to anthropogenic stressors, we developed a spatially-explicit predictive model using gridded environmental variables and organic carbon data from our synthesis Baltic Sediment Blue Carbon Database (>12,500 entries). We further use stable isotopes of H, C and N to quantify and determine the source (terrestrial vs. marine) of OC transported to and buried in Swedish coastal sediments of the Gulf of Bothnia along gradients of riverine discharge with contrasting land-use. This approach helps constrain the impact of climate change on the delivery and fate of terrestrially-derived and aquatic OC in coastal sediments and identifies marine burial hotspots to better understand OC processing along the land-sea continuum.

How to cite: Rouillard, A., Gudasz, C., Ask, J., Huseby, S., Gonzalez Guerrero, L., Karlsson, J., and Kamenos, N. A.: Land-sea continuum: long-term fate of terrestrial organic carbon in coastal environments of the Baltic Sea, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1421, https://doi.org/10.5194/oos2025-1421, 2025.

P127

OOS2025-1454

ECOP

Community Based Mangrove Restoration in the Sundarbans

Clothilde Michelet and Alice Beneyton

EcoAct is an international climate consultancy and project developer dedicated to helping businesses and organizations achieve their climate ambitions. By developing nature-based solutions projects, EcoAct enables companies to leverage natural ecosystems for carbon sequestration, while simultaneously enhancing biodiversity and community resilience. In this process, EcoAct serves as the vital link between companies providing upfront investment and local implementation partners responsible for executing the projects on the ground.

Among the most vital of these natural ecosystems are coastal environments, particularly mangroves, which serve as significant carbon sinks that can store up to five times more carbon than other forests. Their degradation, however, results in substantial carbon emissions, making mangrove restoration an efficient nature-based solution that not only mitigates climate change, but also reduces community vulnerability while restoring vital ecosystem services.

In this context, the Sundari project is being co-developed by EcoAct and Meensou India Private Limited and aims to restore more than 4,000 hectares of degraded mangroves in the Indian Sundarbans through Community Based Mangrove Ecological Restoration. The Sundarbans, right in the convergence of the Ganges and Brahmaputra Rivers, in the border between India and Bangladesh, is the largest mangrove forest of the world but it is also one of the most threatened as the 24 South Parganas is one of the most densely populated Districts of India. Due to the growing development and the exposure to continuous climate risks like floodings, cyclones and coastline erosion, the area is highly vulnerable to climate change.

Sundari combines scientific rigor with active community involvement, ensuring equal opportunities for women and men in implementation and monitoring. The project not only focuses on ecological restoration but also creates sustainable economic opportunities and livelihood diversification for local villages, easing the pressure on mangrove forests and strengthening the natural resilience of these communities.

Certified under the Verified Carbon Standard (VCS) and with an initial duration of 20 years, the project is expected to remove millions of tCO2e. The first phase, Sundari I, launched in November 2023, covers 450 hectares in Sagar Island and Namkhana in the South 24 Parganas district. This initial instance aims to remove greenhouse gases from the atmosphere over two decades by planting more than 1.4 million trees across four sites.

In conclusion, the Sundari Mangrove Restoration Project serves as a model for nature-based solutions that effectively address climate change mitigation and adaptation while ensuring equitable participation and benefits for local communities. By restoring critical coastal ecosystems, engaging local stakeholders, and adhering to rigorous scientific standards, this project demonstrates how ocean-based approaches can significantly contribute to achieving the goals of the Paris Agreement in a sustainable and equitable manner.

How to cite: Michelet, C. and Beneyton, A.: Community Based Mangrove Restoration in the Sundarbans , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1454, https://doi.org/10.5194/oos2025-1454, 2025.

P128

OOS2025-1527

Blue carbon reservoirs – main or side effect

Helmuth Thomas and Bryce van Dam

Biogeochemical interventions directed towards either the protection or intentional enhancement of existing blue carbon reservoirs are often presented as a potential “win-win” scenario for climate change mitigation.

Fundamental to the efficacy of such interventions is the insight that in most cases the temporal change in the “blue” (carbon) inventory is 1-3 orders of magnitudes lower than the changes of the dissolved carbon reservoirs driven by ecosystem processing. These dissolved carbon reservoirs are directly connected with atmospheric CO2 through the marine inorganic carbon system. Hence, the potential of Blue Carbon approaches may be much larger (or smaller) than implied by turnover in the living biomass or residual organic burial terms.

We discuss a suite of locally focused full ecosystem carbon budgeting studies to provide a glimpse into specific processes critical to carbon processing in blue carbon ecosystems. These processes can at times amplify, cancel out, or even reverse the effects of genuine, often easy to measure, biomass accumulation.

As the public desire for blue carbon projects continues to grow, we call for a pressing need for a new integrated approach to carbon accounting, which could ensure that Blue Carbon management results in the desired and marketed climate effects.

How to cite: Thomas, H. and van Dam, B.: Blue carbon reservoirs – main or side effect, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1527, https://doi.org/10.5194/oos2025-1527, 2025.

Posters virtual | online

Display time: Tue, 3 Jun, 17:00–Thu, 5 Jun, 20:00

vP23

OOS2025-1247

ECOP

First assessment of organic carbon stocks and sequestration rates in soils of blue carbon ecosystems in Cuba

Liana Beatriz Carballo Rosado, Yusmila Helguera Pedraza, Alejandro García Moya, Aniel Guillén Arruebarrena, Yoelvis Bolaños Álvarez, Héctor Cartas, Misael Diaz Asencio, Beatriz Martínez Daranas, Yasser Morera Gómez, Carlos Alonso Hernández, Vanessa Hatje, and Pere Masque

Blue carbon ecosystems are important carbon sinks that sequester large amounts of organic carbon in soils over time scales ranging from decades to millennia, offering high potential for climate change mitigation and adaptation strategies. Cuba is considered as one of the world's blue carbon hotspots due to its extensive and well-preserved mangrove and seagrass habitats, as well as the high carbon densities found in its soils. However, quantitative assessments of organic carbon inventories and accumulation rates are still lacking. This study aimed to evaluate organic carbon stocks and sequestration rates through the evaluation of sediment profiles in seagrasses, mangroves and marshes in the Ciénaga de Zapata wetland and the Gulf of Batabanó, representative areas of these marine-coastal ecosystems in Cuba. Organic carbon content and dating by ²¹⁰Pb and ¹³⁷Cs were determined in the sediment profiles. Organic carbon stocks were highest in mangrove soils dominated by Avicennia germinans (mean value of 1014 ± 70 MgC/ha), compared to those dominated by Rhizophora mangle (mean value of 110 ± 3 MgC/ha), marsh soils (mean value of 179 ± 48 MgC/ha), and seagrass soils (mean value of 198 ± 62 MgC/ha). Sequestration rates were also generally higher in mangrove (mean value of 172 ± 132 g Corg m^-2 yr^-1) than in marshes (mean value of 33,8 ± 1,2 g Corg m^-2 yr^-1) and seagrasses (mean value of 26,5 ± 13,3 g Corg m^-2 yr^-1). This study represents a pioneering effort in Cuba, providing essential data on organic carbon stocks and sequestration rates within blue carbon ecosystems. Such information is critical for guiding future research, enhancing management and conservation strategies, and supporting regional climate change mitigation efforts.

How to cite: Carballo Rosado, L. B., Helguera Pedraza, Y., García Moya, A., Guillén Arruebarrena, A., Bolaños Álvarez, Y., Cartas, H., Diaz Asencio, M., Martínez Daranas, B., Morera Gómez, Y., Alonso Hernández, C., Hatje, V., and Masque, P.: First assessment of organic carbon stocks and sequestration rates in soils of blue carbon ecosystems in Cuba, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1247, https://doi.org/10.5194/oos2025-1247, 2025.

vP24

OOS2025-418

ECOP

Carbon sink potential of kelp cultivation in Fujian province, China

Fei Zhang and Kunxian Tang

Macroalgae, such as kelp, are typical carbon sink organisms that play a crucial role in absorbing and sequestering CO₂, thereby mitigating global climate change. China is the world's largest producer of farmed kelp, with Fujian Province leading the country in kelp cultivation, contributing significantly to carbon sequestration. Based on the "China Fisheries Statistical Yearbook" from 2004 to 2024, we estimated the aquaculture carbon sinks of kelp in Fujian over the past two decades, including biomass carbon sinks, sediment carbon sinks, transported carbon sinks, and refractory dissolved organic carbon. We also employed the Autoregressive Integrated Moving Average (ARIMA) model to predict the trend of kelp aquaculture carbon sinks in Fujian from 2024 to 2033. The results indicate that the carbon sinks from kelp aquaculture in Fujian increased from 270,800-287,900 tons in 2004 to 504,700-531,600 tons in 2023, nearly doubling. According to the ARIMA model (0, 2, 1), the carbon sinks from kelp aquaculture in Fujian are expected to continue increasing steadily over the next decade, reaching 562,900-591,400 tons by 2033, which is 2.1 times that of 2004. Assessment of kelp aquaculture carbon sinks and predictions for the next decade's carbon sinks provide a basis for proposing development strategies. This has significant reference value for Fujian Province in efficiently developing the kelp aquaculture carbon sink industry and contributing to the achievement of the "carbon peak and carbon neutrality" goals in China.

How to cite: Zhang, F. and Tang, K.: Carbon sink potential of kelp cultivation in Fujian province, China, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-418, https://doi.org/10.5194/oos2025-418, 2025.

vP25

OOS2025-984

ECOP

Temporal and spatial variations of air-sea CO2 fluxes and their keyinfluence factors in seagrass meadows of Hainan Island, South China Sea

Songlin Liu, Zhijian Jiang, Yunchao Wu, and Xiaoping Huang

Seagrass ecosystems have received a great deal of attention for contributing to uptake of atmospheric CO₂, and thereby helping to mitigate global climate change (‘blue carbon’). Carbon budgets for seagrass ecosystems are developed by estimating air-sea CO₂fluxes. Data for air-sea CO₂ flux for tropical seagrass ecosystems are lacking, which is problematic for constraining global seagrass carbon budgets. Here, we sought to address this important data gap for tropical seagrass ecosystems (dominated by Thalassia hemprichii and Enhalus acoroides) from the Hainan Island of South China Sea, while also testing what the main factors driving the variations of air-sea CO₂fluxes are. We found that air-sea CO₂ fluxes exhibited a U-shape diurnal variability from 6 a.m. to 6 a.m. of the next day, with the highest and lowest air-sea CO₂ fluxes values at early morning and afternoon, respectively. Biological processes were the driving force for mediating diurnal variations of seawater pCO₂. The pCO_{2, sea} in different seasons displayed a trend of increasing from spring, reaching maximum in summer and then a decreasing trend after summer, where water temperature, wind speed and seagrass growth mainly drove the variations. This resulted in net uptake of CO₂ in all seasons except during summer in our study seagrass ecosystems, with greater negative values found in autumn (-3.63 ± 0.76 mmol m^-2 d^-1) than those in winter (-2.84 ± 0.60 mmol m^-2 d^-1). While the nutrient loading induced seagrass biomass changes (especially the seagrass T. hemprichii), which mediated the air-sea CO₂ fluxes changes among different seagrass meadows. Net annual CO₂ uptake potential under low nutrient loading (-0.77 ± 0.16 mol m^-2yr^-1) was 23-54% greater than high nutrient loading seagrass meadows, with the average annual air-sea CO₂ flux of the three seagrass meadows as -0.64 ± 0.13 mol m^-2yr^-1. These results suggest that tropical seagrass meadows of Hainan Island are a significant CO₂ sink of atmospheric CO₂, but this capacity can be diminished by nutrient loading. Scaling up, we estimate the annual atmospheric CO₂ uptake by seagrass meadows of Hainan Island (total area 55.28 km²) was 1,544 tonnes of CO₂ yr^-1, equivalent to the annual emissions from the wholesale, retail, accommodation and catering industries of 164,000 tourists in Hainan Island. With carbon neutrality becoming an important part of global climate governance, this study provides timely information for capitalising on the ability of seagrasses to contribute to natural climate solutions.

How to cite: Liu, S., Jiang, Z., Wu, Y., and Huang, X.: Temporal and spatial variations of air-sea CO2 fluxes and their keyinfluence factors in seagrass meadows of Hainan Island, South China Sea, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-984, https://doi.org/10.5194/oos2025-984, 2025.

vP26

OOS2025-1143

ECOP

Assessing the Effectiveness of Nature-Based Solutions in Reducing Greenhouse Gas Emissions from Shrimp Aquaculture

Abul Bashar and Mohammad Mahfujul Haque

Shrimp aquaculture in South Asian countries has long played a critical role in improving socio-economic conditions and nutritional security, but its contribution to greenhouse gas (GHG) emissions raises concerns about the sustainability of these systems. Nature-based solutions (NbS), such as Najas-based aquaculture and Integrated Multi-Trophic Aquaculture (IMTA), present potential strategies for reducing the carbon footprint of shrimp farming. However, their effectiveness in mitigating GHG emissions has not been well studied. This research investigates the impact of Najas-based NbS and the IMTA system on GHG emissions from shrimp farms in southwestern Bangladesh over a three-month period. Gas samples were collected both day and night using the floating chamber method, and GHG concentrations (CO₂, CH₄, N₂O) were analyzed via gas chromatography-mass spectrometry (GC-MS). Our results show that shrimp farms emit significant amounts of CO₂ (1572.7 ± 273.4 g/day/hectare), CH₄(19.8 ± 4.9 g/day/hectare), and N₂O (1.09 ± 0.35 g/day/hectare). Notably, CO₂emissions were higher at night (1834.7 ± 154.3 g/day/hectare) than during the day (1374.2 ± 341.5 g/day/hectare). Both the Najas-based culture and IMTA systems significantly reduced CO2 emissions during daylight hours (p>0.05). Najas enhanced oxygenation at the sediment-water interface, which helped reduce methane production significantly (p>0.05) during the day, while IMTA reduced organic matter and methane emissions throughout the day and night. No significant reduction in N₂O emissions was observed. When combined, these systems resulted in substantial reductions in both CO₂ and CH₄ emissions. This study demonstrates the potential of integrating Najas-based NbS with IMTA to significantly reduce the carbon footprint of shrimp farming and contribute to more sustainable aquaculture practices.

How to cite: Bashar, A. and Haque, M. M.: Assessing the Effectiveness of Nature-Based Solutions in Reducing Greenhouse Gas Emissions from Shrimp Aquaculture, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1143, https://doi.org/10.5194/oos2025-1143, 2025.