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Societal Impact Statement Summary The invasive species S. alterniflora and P. australis are fast growing coastal wetland plants sequestering large amounts of carbon in the soil and protect coastlines against erosion and storm surges. In this global analysis, we found that Spartina and Phragmites increase methane but not nitrous oxide emissions, with Phragmites having a lesser effect. The impact of the invasive species on emissions differed greatly among different types of native plant groups, providing valuable information to managers and policymakers during coastal wetland planning and restoration efforts. Further, our estimated net emissions per wetland plant group facilitate regional and national blue carbon estimates. Globally, Spartina alterniflora and Phragmites australis are among the most pervasive invasive plants in coastal wetland ecosystems. Both species sequester large amounts of atmospheric carbon dioxide (CO2) and biogenic carbon in soils but also support production and emission of methane (CH4). In this study, we investigated the magnitude of their net greenhouse gas (GHG) release from invaded and non‐invaded habitats. We conducted a meta‐analysis of GHG fluxes associated with these two species and related soil carbon content and plant biomass in invaded coastal wetlands. Our results show that both invasive species increase CH4 fluxes compared to uninvaded coastal wetlands, but they do not significantly affect CO2 and N2O fluxes. The magnitude of emissions from Spartina and Phragmites differs among native habitats. GHG fluxes, soil carbon and plant biomass of Spartina‐invaded habitats were highest compared to uninvaded mudflats and succulent forb‐dominated wetlands, while being lower compared to uninvaded mangroves (except for CH4). This meta‐analysis highlights the important role of individual plant traits as drivers of change by invasive species on plant‐mediated carbon cycles. [ABSTRACT FROM AUTHOR]

We review the functioning and sustainability of coastal marshes and mangroves. Urbanized humans have a 7,000-year-old enduring relationship to coastal wetlands. Wetlands include marshes, salt flats, and saline and freshwater forests. Coastal wetlands occur in all climate zones but are most abundant in deltas. Mangroves are tropical, whereas marshes occur from tropical to boreal areas. Quantification of coastal wetland areas has advanced in recent years but is still insufficiently accurate. Climate change and sea-level rise are predicted to lead to significant wetland losses and other impacts on coastal wetlands and the humans associated with them. Landward migration and coastal retreat are not expected to significantly reduce coastal wetland losses. Nitrogen watershed inputs are unlikely to alter coastal marsh stability because watershed loadings are mostly significantly lower than those in fertilization studies that show decreased belowground biomass and increased decomposition of soil organic matter. Blue carbon is not expected to significantly reduce climate impacts. The high values of ecosystem goods and services of wetlands are expected to be reduced by area losses. Humans have had strong impacts on coastal wetlands in the Holocene, and these impacts are expected to increase in the Anthropocene. [ABSTRACT FROM AUTHOR]

Marine forests are key providers of ecosystem services globally with increasing recognition of their relevance in the context of climate adaptation and mitigation. Along the Southeast Pacific, these forests sustain productive and intricate trophic webs, serving as crucial sustenance for coastal systems and subsidies for deeper habitats. This study aimed to estimate the contribution of Lessonia trabeculata to the local blue carbon pathways within the southern sector of the largest coastal protected area in Peru, Reserva Nacional San Fernando (RNSF). By integrating remote sensing, scientific diving, and the traditional knowledge of artisanal divers, we conducted a comprehensive assessment and conservative estimates of carbon captured by these forests during the austral winter of 2021 using the least destructive assessment methods. We conservatively estimated ~1300 t C captured as standing stock by L. trabeculata in the southern sector of RNSF. Said biomass-held carbon assimilation would annually release ~1300 t C m2 y-1 as detritus, of which, once exported could potentially yield to ~130 t C m2 y-1 sequestered in deep-sea sediments. Detrital productivity of L. trabeculata was calculated for the first time in Peru, along with the social and environmental cost of emissions equivalent to the amount of carbon captured (855.8k US$) and potentially removed by the standing stock (85.7k US$). In addition, we present an overview of the conservation state of the kelp population in the coastal protected area, along with allometric equations for estimating biomass based on biometric measurements easily attainable underwater. This study represents the continuation of a pioneering effort towards the understanding of blue carbon in marine forests of Peru. Our study contributes to advancing the understanding and management of these ecosystems in the face of climate challenges. The implications for the rapidly growing blue carbon field in the region's socioecological context are further discussed. [ABSTRACT FROM AUTHOR]

• Lake Edku, Egypt, sequester carbon which worth of $1.7 million. • NDVI and SAVI indicated that carbon stocks were best predicted during year of 2022. • Land use classification showed that many coastal areas were lost since 1994. As a case study to assess changes of blue carbon stocks among different land use classes; lake Edku, Egypt, was selected at the north Mediterranean coast of Egypt. Landsat 5 and 8 satellites imageries (1994, 2008, and 2022) were downloaded and upon classification, there were five land use classes identified: artificial surfaces (including barren and urban areas), crops, flooded vegetation, sabkha, and water. Using InVEST model, the quantity and economic value of the coastal blue carbon sequestration (CBCS) service offered by lake Edku were modelled. Based on land use classification of lake Edku, those area that were classified as surface water and croplands were decreased from 1994 to 2022. On the other hand, aerial coverage of the artificial surface increased. Analyses for Normalized Difference Vegetation Index (NDVI) and Soil Adjusted Vegeation Index (SAVI) indicated that the amount of carbon stocks estimated by ground inventory was best predicted during year of 2022 (R2= 0.449, P value < 0.01). Our economic analyses of CBCS provided by lake Edku between 1994 and 2022 was 0.6507 (106 Mg C ha−1), which has a value of about $49 millions. Per year, lake Edku sequester carbon that worth about $1.7 million. Our study concluded that CBCS service can hasten the adoption of wetland rehabilitation measures, which have a favourable effect on climate regulation. [ABSTRACT FROM AUTHOR]

In approximately one decade, global temperatures will likely exceed a warming level that a United Nations Intergovernmental Panel on Climate Change report considers a "red alert for humanity". We propose exploring tidal flat diatoms to address climate change challenges. Tidal flats are extensive coastal ecosystems crucial to the provisioning and regulation of aquatic environments. Diatoms contribute to tidal flat biomass production and account for 20% of global primary productivity and 40% of annual marine biomass production, making them crucial for nutrient cycling and sediment stabilization. Potential CO2 removal from Korean tidal flats by diatoms is estimated to be 598,457–683,171 t CO2 equivalents (CO2e) annually, with the economic value of blue carbon (BC) resulting from diatom activity being approximately US$ 17.95–20.50 million. Dissemination of this potential could incentivize coastal wetland protection and climate change mitigation measures. The global estimated CO2e removal potential of tidal flat diatoms is 40,957,346–46,754,961 t CO2e, representing 0.11–0.13% of the annual global greenhouse gas emissions, even though tidal flats cover 0.0025% of the Earth's surface and diatoms represent less than 0.5% (by weight) of all photosynthetic plants. Researchers should combine ecology and economics to develop standardized approaches for carbon input monitoring and quantification. Further, spatiotemporal analyses of environmental threats to tidal flat diatoms are necessary for conserving their biodiversity and function as a critical BC source. Land-based cultivation for large-scale biomass production and biorefinery processes can contribute to a greener, more prosperous future for humanity and the marine ecosystems upon which we rely. [ABSTRACT FROM AUTHOR]

Mangroves on the islands along the Java Sea play a crucial role in supporting biodiversity, protecting coastlines, and sequestering carbon. However, there is a lack of information on mangrove structure and biomass in the area. This study aimed to assess the mangrove structures and biomass on Desa Daun, located on the Bawean Islands, and Kemujan Island, located on the Karimunjawa Islands, respectively. The study utilized a combination of line transect and quadrant plot methods with a size plot of 10x10 m. We established 7 line transects and 28 quadrant plots in the mangrove forest of Desa Daun and similarly set up 7 line transects and 21 quadrant plots on Kemujan Island. Within each quadrant, the mangrove species were identified, and their diameters at breast height (DBH) were recorded. To assess the relative significance of each species, the importance value index (IVI) was calculated, and allometric equations were applied to estimate biomass and carbon storage in the trees. PlanetScope imagery was also used to quantify the carbon stock of mangroves on those islands. In Desa Daun, 13 mangrove species were identified, while 12 species were recorded on Kemujan Island. The species Nypa fruticans and Excoecaria agallocha exhibited the highest IVI in Desa Daun and Kemujan Island, respectively. Notably, Rhizophora apiculata demonstrated the greatest biomass in both locations, with measurements of 43.08 Mg B/ha in Desa Daun and 102.22 Mg B/ha in Kemujan Island. Overall, mangrove stands on Desa Daun stored biomass of 113.60 Mg B/ha and carbon of 50.98 Mg C/ha, whereas mangrove stands on Kemujan Island stored biomass of 295.04 Mg B/ha and carbon of 131.95 Mg C/ha. Mangrove stands of the whole Bawean Islands sequestered 22,941 Mg C, while Karimunjawa Islands hold much higher C stocks, 79,451 Mg C. Despite being smaller in size, the Karimunjawa Islands have more extensive mangrove coverage compared to the Bawean Islands due to their geomorphological characteristics, which in turn influence their mangrove structures and carbon stocks. However, the loss of mangroves in the Karimunjawa Islands due to aquaculture expansions could increase carbon loss in the islands. [ABSTRACT FROM AUTHOR]

Blue carbon refers to the carbon fixed in marine ecosystems such as mangroves, salt marshes, and seagrass beds. Considered a treasure house for capturing and storing carbon dioxide, it can alleviate environmental issues linked to climate change and positively influence the environments where people live. Thus, to clarify the hotspots and development trends of blue carbon research, bibliometric analysis incorporating ScientoPy and VOSviewer software were used to quantitatively analyze 4,604 blue carbon publications from Web of Science and Scopus databases between 1993 and 2023. The results indicate a rapidly growing number of published studies on blue carbon, with blue carbon research being multifaceted and gradually becoming an interdisciplinary and international topic. This study on blue carbon, which is based on keyword clustering analysis, comprises three stages. The analysis of the strength of the cooperative connections between scholars in various countries who have published work on blue carbon. found that the cooperation networks of developed countries are strong and those of developing countries are relatively weak. Quantitative trend analysis reveals a growing focus on the restoration and conservation of blue carbon ecosystems, with remote sensing being the predominant technology used in the blue carbon research field in recent years. In blue carbon research, increasing carbon sequestration capacity, climate change mitigation, and carbon sequestration in macroalgae remain potential hotspots for research and development. [ABSTRACT FROM AUTHOR]

Marsh and mangrove forest habitats are productive at capturing and storing carbon, thus actions to protect and create coastal blue carbon sinks could help mitigate global warming. Dredged material is often used to create coastal habitats and evaluating the carbon impact of placement alternatives (PA) could help inform restoration and climate policies. Output from a Delft3D‐FM morphodynamics and hydrodynamics model informed a Coastal Wetlands Carbon Model at years 2020, 2025, 2030, and 2050. Three model simulations were used and included (1) no restoration (PA1), (2) restoration dominated with mangroves (PA2), and (3) restoration dominated with marshes (PA3) at a different location. Habitats of brackish marsh, saline marsh, mangrove forest, and saline open water that surround Port Fourchon, Louisiana, U.S.A., were evaluated to estimate the net greenhouse gas (GHG) flux of the study area with and without restoration. In years 2020 and 2025, the study area was estimated to be a net GHG sink (−1.1 ± 0.2 MMT CO2e) with or without mangrove and marsh‐dominated restoration. At years 2030 and 2050, even with habitat loss due to sea‐level rise, the study area for all simulations was projected to remain a net GHG sink. At year 2050, +0.1 ± 0.04 MMT CO2e could be avoided with restoration. At the restoration project scale, mangrove‐dominated restoration (PA2) had net GHG sinks (−0.07 to −0.09 MMT CO2e) near the marsh‐dominated restoration (PA3, −0.09 to −0.13 MMT CO2e). Thus, these modeled results could help inform future restoration planning and climate policies. [ABSTRACT FROM AUTHOR]

High-latitude ecosystems have been overlooked in carbon budgets, which traditionally focus on mangroves, salt marshes, and seagrasses. The benthic assemblages and their Nature Contributions to People in Namuncurá – Burdwood Bank I and II, two offshore sub-Antarctic Marine Protected Areas (MPAs), are the conservation values. Here we show that the carbon reservoirs of these MPAs can be greater than those of their Antarctic counterparts, which, together with their extension, emphasize the need to maintain their protected status. Considering their total area, these MPAs stored in biomass 52,085.78 Mg C, corresponding 34,964.16 Mg to organic carbon (OC) and 17,121.62 Mg to inorganic carbon (IC). Surficial sediments stored 933,258,336 Mg C with 188,089,629 Mg of OC and 745,168,707 Mg of IC. However, when accounting for CO2 production through CaCO3 precipitation, the IC fractions decrease to 3,150.37 Mg C and 137,111,042 Mg C for biomass and sediments, respectively. We assume low sediment deposition due to the oceanic location, as direct sedimentation rates for these areas are unavailable. Most blue carbon assessments have focused solely on OC, despite the formation of CaCO3 releases CO2, decreasing net carbon storage. We compared various approaches for incorporating carbonates into carbon estimations. These results underscore the importance of including IC into carbon assessments and highlights the importance of sub-Antarctic benthic ecosystems as nature-based solutions to climate change. [ABSTRACT FROM AUTHOR]

Large grazers modify vegetated ecosystems and are increasingly viewed as keystone species in trophic rewilding schemes. Yet, as their ecosystem influences are context‐dependent, a crucial challenge is identifying where grazers sustain, versus undermine, important ecosystem properties and their resilience. Previous work in diverse European saltmarshes found that, despite changing plant and invertebrate community structure, grazers do not suppress below‐ground properties, including soil organic carbon (SOC). We hypothesised that, in contrast, eastern US saltmarshes would be sensitive to large grazers as extensive areas are dominated by a single grass, Spartina alterniflora. We predicted that grazers would reduce above‐ and below‐ground Spartina biomass, suppress invertebrate densities, shift soil texture and ultimately reduce SOC concentration. We tested our hypotheses using a replicated 51‐month large grazer (horse) exclusion experiment in Georgia, coupled with observations of 14 long‐term grazed sites, spanning ~1000 km of the eastern US coast. Grazer exclusion quickly led to increased Spartina height, cover and flowering, and increased snail density. Changes in vegetation structure were reflected in modified soil texture (reduced sand, increased clay) and elevated root biomass, yet we found no response of SOC. Large grazer exclusion also reduced drought‐associated vegetation die‐off. We also observed vegetation shifts in sites along the eastern US seaboard where grazing has occurred for hundreds of years. Unlike in the exclusion experiment, long‐term grazing was associated with reduced SOC. A structural equation model implicated grazing by revealing reduced stem height as a key driver of reduced soil organic carbon. Synthesis: These results illustrate the context dependency of large grazer impacts on ecosystem properties in coastal wetlands. In contrast to well‐studied European marshes, eastern US marshes are dominated and structured by a single foundational grass species resulting in vegetation and soil properties being more sensitive to grazing. Coastal systems characterised by a single foundation species might be inherently vulnerable to large grazers and lack resilience in the face of other disturbances, underlining that frameworks to explain and predict large grazer impacts must account for geographic variation in ecosystem structure. [ABSTRACT FROM AUTHOR]

Mangroves provide numerous ecological, social, and economic benefits that include carbon sequestration, habitat for biodiversity, food, recreation and leisure, income, and coastal resilience. In this regard, mangrove-based carbon market projects (MbCMP), involving mangrove conservation, protection, and restoration, are a nature-based solution (NbS) for climate change mitigation. Despite the proliferation of blue carbon projects, a highly publicized need for local community participation by developers, and existing project implementation standards, local communities are usually left out for several reasons, such as a lack of capacity to engage in business-to-business (B2B) market agreements and communication gaps. Local communities need to be engaged and supported at all stages of the MbCMP development process to enable them to protect their ecological, economic, and social interests as custodians of such a critical ecosystem. In this paper, we provided 15 strategic considerations and recommendations to engage and secure the interests of local communities in the growing mangrove carbon market trade. The 15 considerations are grouped into four recommendation categories: (i) project development and community engagement, (ii) capacity building and educational activities, (iii) transparency in resource allocation and distribution, and (iv) partnerships with local entities and long-term monitoring. We expect our study to increase local participation and community-level ecological, social, and economic benefits from MbCMP by incorporating equitable benefit-sharing mechanisms in a B2B conservation-agreement model. [ABSTRACT FROM AUTHOR]

Coastal marine habitats (i.e. mangroves, saltmarshes, and seagrasses) have a high capacity for carbon sequestration (termed "blue carbon") and the potential to reduce the effects of greenhouse gas emissions. However, blue carbon habitats have historically decreased as a consequence of land conversion, coastal development, and pollution and are under threat in many locations. Restoration of these habitats can reverse historic losses and generate carbon credits through increased carbon sequestration. With a long coastline, we hypothesized that there would be significant opportunities for coastal blue carbon in Aotearoa New Zealand. Results revealed Aotearoa estuaries and coastal areas contain approximately 20,932 ha of saltmarsh, 30,533 ha of mangrove, and 61,340 ha of seagrass, estimated to sequester a total of approximately 57,800 tC/year. A further 87,861 ha of land was estimated to be potentially suitable for blue carbon projects via tidal restoration, of which 56,482 ha was suitable for saltmarsh restoration (equivalent to 60,435 tC yr if restored), 17,291 ha was suitable for mangroves (26,455 tC/year), and 14,087 ha was suitable for seagrass (4790 tC/year). Both existing extent and restoration opportunity varied throughout the country, with greater opportunity in some regions than others. Nationwide, the total sequestration potential for blue carbon restoration was estimated at 91,680 tC yr−1 if all potential areas were restored. Carbon credits generated by blue carbon projects could be traded on a carbon market in Aotearoa, generate revenue for landowners, provide an additional pathway to meet domestic and international climate change targets, and result in a diversity of other ecological, social, and cultural co‐benefits from coastal restoration. [ABSTRACT FROM AUTHOR]

Consumers can directly (e.g., consumption) and indirectly (e.g., trophic cascades) influence carbon cycling in blue carbon ecosystems. Previous work found that large grazers have nuanced effects on carbon stocks, yet, small, bioturbating‐grazers, which remove plant biomass and alter sediment properties, remain an understudied driver of carbon cycling. We used field‐derived and remote sensing data to quantify how the purple marsh crab, Sesarma reticulatum, influenced carbon stocks, flux, and recovery in salt marshes. Sesarma caused a 40%–70% loss in carbon stocks as fronts propagated inland (i.e., ungrazed to recovered transition), with front migration rates accelerating over time. Despite latitudinal differences, front migration rate had no effect on carbon stocks, flux, or time to replacement. When we included Sesarma disturbance in carbon flux calculations, we found it may take 5–100 years for marshes to replace lost carbon, if at all. Combined, we show that small grazers cause a net loss in carbon stocks as they move through the landscape, and irrespective of migration rate, these grazer‐driven impacts persist for decades. This work showcases the significant role of consumers in carbon storage and flux, challenging the classic paradigm of plant–sediment feedbacks as the primary ecogeomorphic driver of carbon cycling in blue carbon ecosystems. [ABSTRACT FROM AUTHOR]

The scale at which New Zealand is currently storing and sequestering blue carbon, and could create additional blue carbon via restoration, has been unclear. Here, we calculate a preliminary estimate for the current extent of three key blue carbon ecosystems (saltmarshes, mangrove forests and seagrass meadows), their carbon stocks and their carbon sequestration rates using the best available data to provide a preliminary estimate of blue carbon in New Zealand. We also use local examples to explore opportunities to create additional blue carbon. Based on the available literature, we estimate the current extent of New Zealand's blue carbon ecosystems to be 76,152 ha, which is 1.0% of the area of terrestrial native forests. Our preliminary estimate of New Zealand's blue carbon stock is 2.66–3.76 Mt of carbon, with a current carbon sequestration rate of 0.12 (0.05–0.26) Mt/CO2/yr, which is equivalent to 0.16% of New Zealand's 2021 gross emissions. Restoration of saltmarshes could enhance their carbon sink capacity, mangrove forests are naturally expanding and seagrass meadow restoration techniques at scale are still in development. Developing a national framework for blue carbon protection, monitoring and restoration is important as part of New Zealand's climate change mitigation and adaptation efforts. [ABSTRACT FROM AUTHOR]

Mangroves are a crucial part of the coastal ecosystem; thus, precise and up-to-date monitoring is essential to guide regional policies and inform conservation strategies. This study investigates the capabilities of semi-automated remote sensing approaches within a Google Earth Engine framework for national-scale mangrove mapping in Thailand. Remote sensing data from 2018—10,000 data points acquired from Sentinel-1, Sentinel-2, and the Shuttle Radar Topography Mission (SRTM)—was used to train several machine learning models. The Gradient Tree Boost (GTB) proved to be the most reliable, with the least variation in validity (the lowest IQR) and the highest average Overall Accuracy of 96.75 ± 0.63 % compared to the others—96.64 ± 0.72 % for Random Forest (RF); 96.12 ± 0.80 %for Classification and Regression Trees (CART); and 95.43 ± 0.74 % for Support Vector Machines (SVM). Thus, the GTB was instrumental in mapping mangrove distribution with 10-m spatial resolution across Thailand from 2016 to 2022, the period in which the mangrove areas increased by 11 %, reflecting successful conservation efforts over the past decade. The developed framework establishes the foundation for semi-automated mangrove mapping that can be developed for other geographical contexts. [ABSTRACT FROM AUTHOR]

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The role of coastal mangrove wetlands in sequestering atmospheric carbon dioxide has been increasingly investigated in recent years. While studies have shown that mangroves are weak sources of methane (CH4) emissions, measurements of CH4 fluxes from these ecosystems remain scarce. In this study, we examined the temporal variation and biophysical drivers of ecosystem-scale CH4 fluxes in China's northernmost mangrove ecosystem based on eddy covariance measurements obtained over a 3-year period. In this mangrove, the annual CH4 emissions ranged from 6.15 to 9.07 g C m−2 year−1. The daily CH4 flux reached a peak of over 0.07 g C m−2 day−1 during the summer, while the winter CH4 flux was negligible. Latent heat, soil temperature, photosynthetically active radiation, and tide water level were the primary factors controlling CH4 emissions. This study not only elucidates the mechanisms influencing CH4 emissions from mangroves, strengthening the understanding of these processes but also provides a valuable benchmark dataset to validate the model-derived carbon budget estimates for these ecosystems. [ABSTRACT FROM AUTHOR]

Upper estuarine forested wetlands (UEFWs) play an important role in the sequestration of atmospheric carbon (C), which is facilitated by their position at the boundary of terrestrial and maritime environments but threatened by sea level rise. This study assessed the change in aboveground C stocks along the estuarine–riverine hydrogeomorphic gradient spanning salt-impacted freshwater tidal forested wetlands to freshwater forested wetlands in seasonally tidal and nontidal landscape positions. Standing stocks of C in forested wetlands were measured along two major coastal river systems, the Winyah Bay in South Carolina and the Savannah River in Georgia (USA), replicating and expanding a previous study to allow the assessment of change over time. Aboveground C stocks on these systems averaged 172.9 Mg C ha−1, comparable to those found in UEFWs across the globe and distinct from the terrestrial forested ecosystems they are often considered to be a part of during large-scale C inventory efforts. Groundwater salinity conditions as low as 1.3 ppt were observed in conjunction with losses of aboveground C. When viewed in context alongside expected sea level rise and corresponding saltwater intrusion estimates, these data suggest a marked decrease in aboveground C stocks in forested wetlands situated in and around tidal estuaries. [ABSTRACT FROM AUTHOR]

In recent years the blue bioeconomy has been presented as a way for marine-based industries to break with traditional models of relentless resource extraction and extensive damage on marine ecosystems. Centering in innovation and biotechnological enhancement, the concept promises a future that makes compatible continual economic growth with environmental sustainability. In practice, however, the blue bioeconomy still mostly an object of imagination than a reality. In this paper we analyze a leading cause for such lack of effectiveness: the reductionistic ways in which most blue bioeconomy proposals engage with the agencies of marine entities. Adopting an analytical frame from science and technology studies (STS), we understand the multiple strategies oriented to produce neat and simple versions of marine beings as forms of “pacification” that enable the transformation of these beings in commodities that could be easily traded in global markets, at the expense of their sociobiological complexity. To explore the ways in which pacification works, the paper analyzes current attempts at renovating the seaweed industry in Chile. Especially we analyze two policy proposals – one focused on turning seaweed into the basis of a blue carbon economy and the other centered on the potential of seaweed as high-end novel foods for export – showing how they produce a highly pacified versions of seaweed that bear little resemblance with the complex beings populating Chilean seas. Pacified seaweed comes handy for market-oriented policy proposals but tend to fare quite poorly beyond them. [ABSTRACT FROM AUTHOR]

Mangrove‐dominated coastlines have high carbon sequestration capacity, but it remains unclear whether tidally outwelled carbon is transformed within the coastal ocean or exported offshore. Here, we used radium isotopes (224Ra and 223Ra) to investigate carbon outwelling in two mangrove seascapes in Brazil across multiple spatial scales. We sampled porewaters to define the source composition, mangrove creek waters to resolve tidal cycles, and cross‐shelf transects to trace outwelling in coastal seascapes. Radium isotopes were positively correlated with dissolved inorganic (DIC), organic (DOC) and particulate organic (POC) carbon across the seascapes. DIC was the primary form of carbon (mean ± SD), representing 85% of the total carbon pool as bicarbonate (75 ± 11%), carbonate (6 ± 5%), and CO2 (4 ± 9%). DOC and POC accounted for 10 ± 6% and 5 ± 6% of total carbon, respectively. Although mangrove waters emitted CO2 to the atmosphere (38–143 mmol m−2 d−1), both bays and continental shelves were a CO2 sink (−2.5 to −0.5 mmol m−2 d−1) associated to chlorophyll‐a enrichments (r2 = 0.86). Total carbon outwelled from mangroves were 3–4 times higher than soil carbon burial at both mangrove sites. Bicarbonate export (27–72 mmol m−2 d−1) to the continental shelf was the major fate of carbon outwelling, more than doubling the perceived capacity of mangrove soil to sequester carbon. Hence, disregarding outwelling as a blue carbon sink mechanism would lead to underestimated assessments of how mangroves capture CO2 and help to mitigate climate change. Plain Language Summary: Mangrove forests effectively store large amounts of carbon within their muddy soils due to their complex root systems, high sedimentation rates, and high productivity. Mangroves also play a crucial role in exporting carbon to the ocean through tidal flushing and climate change mitigation. Here, we measured overlooked lateral carbon fluxes using geochemical tracers. Our findings demonstrated that mangroves could sequester 3–4 times more CO2 if total carbon exports to ocean are accounted in addition to soil carbon burial. Most of the carbon is exported as bicarbonate, with the potential to remain in seawater for millennia. We argue that a fraction of mangrove carbon is not lost during transport offshore, but rather stored in the ocean, the largest global carbon reservoir. Key Points: Porewater exchange is a pivotal component of the carbon budget within mangrove seascapesMangrove carbon outwelling oscillates between tidal cycles and reaches the continental shelf within 1–3 weeksCarbon sequestration via outwelling to the ocean was 3–4 times greater than soil burial [ABSTRACT FROM AUTHOR]

Concern for the future requires local steward-led cooperation between natural and social scientists and decision-makers to develop informed and policy-relevant nature-based mitigation solutions, including blue carbon (BC), which can help secure the future. Salt marshes, kelp forests, and seagrass meadows (and to a lesser extent mangroves) are significant BC ecosystems in temperate areas. We discuss the concept of blue carbon stocks and the scientific approaches to building BC stocks considering the variability in local conditions and the co-benefits of blue carbon ecosystems to improve climate change mitigation and adaptation mechanisms. The study examines (1) methods to assess the potential of BC ecosystems and the impact of disturbances, while (2) building relevant policy based on socio-economic assessments of impacted communities. We highlight economic and social approaches to rebuilding BC using financial tools such as blue bonds, development plans, cost-benefit analyses, cross-ecosystem restoration projects, AI and blockchain, and economic accounts of coastal ecosystems, while emphasizing that cutting carbon emissions is more important than (re)building BC stocks. [ABSTRACT FROM AUTHOR]

Anthropogenic activities are driving significant changes in coastal ecological environments, increasingly spotlighting microorganisms associated with seagrass bed ecosystems. Labyrinthula is primarily recognized as a saprophytic protist associated with marine detritus, and it also acts as an opportunistic pathogen affecting marine algae, terrestrial plants and mollusks, especially in coastal environments. The genus plays a key role in the decomposition of marine detritus, facilitated by its interactions with diatoms and through the utilization of a diverse array of carbohydrate-active enzymes to decompose seagrass cell walls. However, human activities have significantly influenced the prevalence and severity of seagrass wasting disease (SWD) through factors such as climate warming, increased salinity and ocean acidification. The rise in temperature and salinity, exacerbated by humaninduced climate change, has been shown to increase the susceptibility of seagrass to Labyrinthula, highlighting the adaptability of pathogen to environmental stressors. Moreover, the role of seagrass in regulating pathogen load and their immune response to Labyrinthula underscore the complex dynamics within these marine ecosystems. Importantly, the genotype diversity of seagrass hosts, environmental stress factors and the presence of marine organisms such as oysters, can influence the interaction mechanisms between seagrass and Labyrinthula. Besides, these organisms have the potential to both mitigate and facilitate pathogen transmission. The complexity of these interactions and their impacts driven by human activities calls for the development of comprehensive multi-factor models to better understand and manage the conservation and restoration of seagrass beds. [ABSTRACT FROM AUTHOR]

Mangroves are implemented as nature‐based solutions (NbS) for coastal protection, climate change mitigation (carbon sequestration) and other services. They play a core role in providing benefits for biodiversity, livelihoods and human well‐being. Ecological research has informed the use of mangroves as NbS, but failure of NbS projects has often been due to misconceptions about mangrove ecology and the limited use of the wide range of ecological knowledge available. Enhanced knowledge of the spatial and temporal variation in ecological processes, and differentiation among mangrove tree species and assemblages (including fauna and microbial communities) in the provision of ecosystem functions and services, will support successful use of mangroves as NbS. Knowledge of mangrove responses to the interacting pressures of climate change and human uses of the coastal zone will support resilient NbS projects. Synthesis. The success of mangroves as NbS can be improved with increased incorporation of knowledge of the ecology of mangrove plants, animals and microbes and by sharing and co‐producing knowledge within mangrove societies. [ABSTRACT FROM AUTHOR]

The natural capacity of marine sediments to capture, sequester, and store organic carbon has been recognized by researchers and policy makers for its potential to mitigate against climate change. As a result, Marine Spatial Planning (MSP) and Marine Protected Area (MPA) designation processes increasingly aim to protect "blue carbon" stored in marine sediments by reducing anthropogenic activities that disturb the seabed (e.g., bottom trawling). In this research, we engaged with coastal residents around Dundalk Bay, Ireland to explore public perceptions of the presence and management of carbon-storing marine sediments in the context of the multifaceted relationship between communities and the environment. This has not been previously studied in an empirical setting. Given the largely "unknown" character of this source of blue carbon, we theorized that speculation played a key role in sustaining emerging perceptions of the sediments, by creating a link with existing place meanings. We used interviews (n = 12) and a focus group (n = 7). Reflexive thematic analysis of the data showed that local residents associated multiple, overlapping meanings with Dundalk Bay. We found evidence that speculative mechanisms such as analogy and experiential knowledge were used to bridge between existing place meanings and emerging perceptions of carbon-storing marine sediments, which also helped indicate the valence of people's feelings about the sediments. We found different views about the presence of the sediments, and residents varied in their prioritization of measures to protect either nature or economic activity in the bay. Because of scientific knowledge gaps related to the distribution and character of marine sediments and the impacts of anthropogenic activity, participants stressed the need for further research and a careful approach to the management of the bay and its sediments. Our work reiterates the importance of recognizing existing people-place connections to understand potential responses to changes in the use and/or management of marine environments. This can help achieve a more engaged and socially acceptable MSP process. [ABSTRACT FROM AUTHOR]

Climate change has become a major agenda item in international relations and in national energy policy-making circles around the world. This review studies the surprising evolution of the energy policy, and more particularly the energy transition, currently happening in the Arabian Gulf region, which features some of the world's largest exporters of oil and gas. Qatar, Saudi Arabia, and other neighboring energy exporters plan to export blue and green hydrogen across Asia as well as towards Europe in the years and decades to come. Although poorly known and understood abroad, this recent strategy does not threaten the current exports of oil and gas (still needed for a few decades) but prepares the evolution of their national energy industries toward the future decarbonized energy demand of their main customers in East and South Asia, and beyond. The world's largest exporter of Liquefied Natural Gas, Qatar, has established industrial policies and projects to upscale CCUS, which can enable blue hydrogen production, as well as natural carbon sinks domestically via afforestation projects. [ABSTRACT FROM AUTHOR]

Upper layer thickness (mixing depth) is an essential parameter for estimating the dissolved inorganic carbon and carbon flux at the water surface based on their association with the vertical flux of dissolved inorganic carbon. Previous studies quantified the mixing depth without SAV meadow or penetration depth in the SAV meadow without stratification and wind stress. However, mixing depth related to interaction with submerged aquatic vegetations (SAVs), stratification, and wind stress has yet to be quantified in the previous studies. Our study is the first to quantify the theoretical mixing depth with SAVs according to wind stress, SAV height, and drag coefficient. Theoretical mixing depth was quantified from modeled vertical temperature profile, vertical profile of horizontal velocity, and gradient Richardson number (Rig,veg). We found that mixing depth at a Rig,veg of 100 demonstrated good agreement with numerical results on average, with the mixing depth estimated in this study (hU,this study) showing high applicability to observations at Komuke Lagoon. Moreover, hU,this study increased with the increasing wind stress and decreasing drag coefficient and SAV height. Further, we found that SAV meadows with stratification and wind stress could be divided into four hydrodynamic regimes: non‐vegetated layers, upper vegetated layers, thermoclines, and benthic boundary layers. Our findings help us estimate mixing depth or vertical flux without complicated numerical simulation and understand flow interaction with SAV, wind stress, and stratification. Plain Language Summary: Upper layer thickness (mixing depth) and flow fields are important to estimate the carbon flux (e.g., "blue carbon") and the transportation of dissolved materials (e.g., dissolved oxygen, dissolved inorganic carbon, dissolved inorganic nitrogen, etc) in submerged aquatic vegetation (SAV) meadows. However, it may not be easy to estimate mixing depth without complex numerical simulations. Additionally, we have not understood the interaction of SAV meadows with stratification, currents, or waves. Our study is the first to quantify the mixing depth analytically and to show the hydrodynamic regimes in SAV meadows with stratification. Our finding helps us to estimate carbon flux and the transportation rate of dissolved materials easily without complicated numerical simulation. Key Points: Mixing depth with submerged aquatic vegetation (SAV) meadows was estimated using an average gradient Richardson number 100SAV meadows with stratification and wind stress were divided into four hydrodynamic regimesWind stress, SAV, and stratification effects were used to accurately estimate the mixing depth [ABSTRACT FROM AUTHOR]

Global climate change and coastal urbanization have significantly impacted the health and carbon storage of coastal zone ecosystems. Investigating the spatial and temporal variations in coastal carbon storage is crucial for developing effective strategies for land management and ecological protection. Current methods for evaluating carbon storage are hindered by insufficient accuracy and data acquisition challenges, necessitating solutions to enhance both reliability and precision. This study aims to assess the variations in carbon storage and annual carbon sequestration in the Jiaozhou Bay coastal zone from 1990 to 2020 and to identify the driving factors by integrating the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) and Carnegie Ames Stanford Approach (CASA) models with remote sensing data and geographic detector methods. The findings suggest that Jiaozhou Bay has experienced a substantial decrease in carbon storage, declining by 17.4% from 1990 to 2020, and annual carbon sequestration, decreasing by 35.5% from 1990 to 2016, but has stabilized recently. Vegetation cover and water bodies play critical roles in regional carbon storage. Furthermore, the dynamics of carbon storage and land use patterns are significantly influenced by socioeconomic factors, including GDP and population density. A comparison of the InVEST and CASA models demonstrates consistency in their carbon storage and annual carbon sequestration assessments. Combining these models in future assessments can enhance the scientific rigor and accuracy of the research, providing more reliable evidence for ecosystem management and policy making. [ABSTRACT FROM AUTHOR]

The blue carbon ecosystems possess the potential to mitigate climate change impacts, support adaptation, assist in reaching the national and global net-zero goals, and secure social, economic, and environmental outcomes through sequestering and storing carbon in sediments. The marine environment along the Red Sea coast of Egypt is distinguished by a high biodiversity with key marine ecosystems such as seagrasses meadows, coral reefs, and mangroves that can play a role in blue carbon ecosystems. To understand the capacity of the seagrasses to store carbon, this study aims at quantifying the vertical distribution of the organic carbon density (OCD) and the carbon sequestration potential (CSR) and evaluate the economic feasibility of seagrasses vegetation as a tool for mitigating climate change. Two sediment cores were sampled from vegetated areas (inhabited with seagrasses species: Thalassia hemprichii) and one core from a non-vegetated area (for comparison) from three nearshore locations within Wadi El Gemal Protected Area, Red Sea Egypt. The OCD in the vegetated areas increased with depth and showed higher capacities of carbon storage compared to the non-vegetated area. The overall calculated CSR for seagrasses in Wadi El-Gemal is 341.65 g C m−2 yr−1. These findings support the key role of seagrasses to mitigate climate change through CO2 sequestration and return an equivalent of 6,000 to 11,000 USD per year for every 100 hectares in monetary value. This highlights the importance of the conservation and restoration of seagrasses along the Red Sea coast and the potential of blue carbon finance that can be leveraged to meet national-level climate mitigation strategies and policies in Egypt. [ABSTRACT FROM AUTHOR]

The extracellular release of dissolved organic carbon (DOC) from marine macroalgae supports coastal ecosystem function by supplying photosynthetically fixed carbon to higher trophic levels via the microbial loop. Despite its widely acknowledged biogeochemical importance, DOC is not typically included in primary production estimates of coastal systems. Additionally, little is known about how changes in species composition and coverage will affect the supply of DOC to coastal systems. Within the context of the Baltic Sea, anthropogenic forces are driving a decline in habitat forming kelp species (Fucus vesiculosus) which is superseded by filamentous/turfing algal species, a pattern of change observed globally in numerous other aquatic systems. To evaluate how the drivers of this change may impact the flow of carbon within the Baltic Sea coastal system, the production of DOC by the filamentous algae (Ectocarpus siliculosus) was examined and its rate of release determined (0.095 mg C · g DW-1 · h-1 in light and 0.070 mg C · g DW-1 · h-1 in dark). In addition, bioassays were used to assess the short-term DOC use by bacteria as a proxy of the lability of the released products, with the majority (28.7% released in light and 18.6% released in dark) of the products remaining after 120 hours. This data was linked with long term macroalgae biomass and coverage surveys in order to assess changes in macroalgae community structure through time and to produce standing stock estimates of F. vesiculosus. DOC production as a metric of algal coverage was used to make a preliminary estimation of how changes in community structure may impact the flow of carbon within the system. Our results suggest that decreased levels of DOC released by filamentous algae relative to F. vesiculosus will act to reduce microbial activity. Our model estimates the presence of approximately 150,000 tonnes of F. vesiculosus (dry weight) within the Estonian coastal system translating to an annual release of 7,391 tonnes of DOC. Our study indicates that filamentous-dominated systems have likely altered carbon flow, impacting the broader ecology of the Baltic Sea. Consequently, the loss of kelp species and the expansion of filamentous algae may alter carbon dynamics, with important ecological consequences for other coastal systems globally. [ABSTRACT FROM AUTHOR]

Abstract High-latitude ecosystems have been overlooked in carbon budgets, which traditionally focus on mangroves, salt marshes, and seagrasses. The benthic assemblages and their Nature Contributions to People in Namuncurá – Burdwood Bank I and II, two offshore sub-Antarctic Marine Protected Areas (MPAs), are the conservation values. Here we show that the carbon reservoirs of these MPAs can be greater than those of their Antarctic counterparts, which, together with their extension, emphasize the need to maintain their protected status. Considering their total area, these MPAs stored in biomass 52,085.78 Mg C, corresponding 34,964.16 Mg to organic carbon (OC) and 17,121.62 Mg to inorganic carbon (IC). Surficial sediments stored 933,258,336 Mg C with 188,089,629 Mg of OC and 745,168,707 Mg of IC. However, when accounting for CO2 production through CaCO3 precipitation, the IC fractions decrease to 3,150.37 Mg C and 137,111,042 Mg C for biomass and sediments, respectively. We assume low sediment deposition due to the oceanic location, as direct sedimentation rates for these areas are unavailable. Most blue carbon assessments have focused solely on OC, despite the formation of CaCO3 releases CO2, decreasing net carbon storage. We compared various approaches for incorporating carbonates into carbon estimations. These results underscore the importance of including IC into carbon assessments and highlights the importance of sub-Antarctic benthic ecosystems as nature-based solutions to climate change.

Mangroves are a crucial part of the coastal ecosystem; thus, precise and up-to-date monitoring is essential to guide regional policies and inform conservation strategies. This study investigates the capabilities of semi-automated remote sensing approaches within a Google Earth Engine framework for national-scale mangrove mapping in Thailand. Remote sensing data from 2018—10,000 data points acquired from Sentinel-1, Sentinel-2, and the Shuttle Radar Topography Mission (SRTM)—was used to train several machine learning models. The Gradient Tree Boost (GTB) proved to be the most reliable, with the least variation in validity (the lowest IQR) and the highest average Overall Accuracy of 96.75 ± 0.63 % compared to the others—96.64 ± 0.72 % for Random Forest (RF); 96.12 ± 0.80 %for Classification and Regression Trees (CART); and 95.43 ± 0.74 % for Support Vector Machines (SVM). Thus, the GTB was instrumental in mapping mangrove distribution with 10-m spatial resolution across Thailand from 2016 to 2022, the period in which the mangrove areas increased by 11 %, reflecting successful conservation efforts over the past decade. The developed framework establishes the foundation for semi-automated mangrove mapping that can be developed for other geographical contexts.

The soil redox potential in wetlands such as peatlands or salt marshes exerts a strong control over microbial decomposition processes and consequently soil carbon cycling. Wetland plants can influence redox by supplying both terminal electron acceptors (i.e. oxygen) and electron donors (i.e. organic matter) to the soil system. However, quantitative insight into the importance of plant effects on wetland soil redox and associated plant traits are scarce. In a combined mesocosm and field study we investigated the impact of plants on soil reduction using IRIS (Indicator of Reduction in Soils) sticks. Vegetated plots were compared to non-vegetated plots along an elevational gradient in a salt marsh of the Wadden Sea and along an artificially created gradient in a tidal tank mesocosm experiment. Our findings from the mesocosm experiment demonstrated that vegetation both enhanced and suppressed soil reduction relative to non-vegetated control pots. The direction of the plant effect (i.e., net oxidizing or net reducing) was inversely correlated with background redox conditions. Insights from high-resolution oxygen profiling via planar optode imaging corroborated these findings. In the field study, vegetation consistently reduced the comparatively well-aerated Wadden Sea salt marsh soil. Reduction correlated positively with soil organic matter content and belowground biomass, indicating that greater availability of plant-derived electron donors, in the form of organic matter, increased soil reduction. Challenging the dominant paradigm that wetland plants primarily act as soil oxidizers, our study reveals their potential to exert a net reducing effect. The documented impact of these plant-induced changes in soil redox conditions suggests a previously overlooked role in shaping the stability of soil organic carbon stocks in wetland ecosystems with variable water tables. [ABSTRACT FROM AUTHOR]

Mesopelagic fishes are a vital component of the biological carbon pump and are, to date, largely unexploited. In recent years, there has been an increased interest in harvesting the mesopelagic zone to produce fish feed for aquaculture. However, great uncertainties exist in how the mesopelagic zone interacts with the climate and food webs, presenting a dilemma for policy. Here, we investigate the consequences of potential policies relating to mesopelagic harvest quotas with a dynamic social-ecological modeling approach, combining system dynamics and global sensitivity analyses informed by participatory modeling. Our analyses reveal that, in simulations of mesopelagic fishing scenarios, uncertainties about mesopelagic fish population dynamics have the most pronounced influence on potential outcomes. The analysis also shows that prioritizing the development of the fishing industry over environmental protection would lead to a significantly higher social cost of climate change to society. Given the large uncertainties and the potential large impacts on oceanic carbon sequestration, a precautionary approach to developing mesopelagic fisheries is warranted. [ABSTRACT FROM AUTHOR]

Coastal wetlands are the main distribution of blue carbon in coastal zones and well known for their high carbon sequestration capacity. Investigating the variation of carbon budget is crucial for understanding the functionality of coastal wetlands and effectively addressing climate change. In this study, a bibliometric analysis of 4,509 articles was conducted to reveal research progress, hot issues, and emerging trends in the coastal wetland carbon budget field. The number of publications and citations in this field increased exponentially from 1991 to 2022. The leading subject category was Environmental Sciences with 1,844 articles (40.9%). At present, studies have been focused on blue carbon, the effects of climate change and man-made disturbances on carbon cycle, and the restoration of coastal wetlands. Based on the hotspots and trends in this field, the future researches should include (1) exploring the functional mechanisms of various factors affecting carbon cycle and establishing a methodological system for the estimation of blue carbon in coastal wetlands; (2) researching restoration techniques of coastal wetland and constructing wetland restoration evaluation index system; and (3) formulating enforceable carbon trading policy and strengthening international cooperation. HIGHLIGHTS Bibliometric analysis of the carbon budget of coastal wetlands was conducted.; The number of publications and citations increased exponentially from 1991 to 2022.; Research hotspots of coastal wetlands shifted from greenhouse gases to blue carbon.; More attention should be paid to restoration techniques of coastal wetlands.;

Abstract Background Mangrove ecosystems exhibit significant carbon storage and sequestration. Its capacity to store and sequester significant amounts of carbon makes this ecosystem very important for climate change mitigation. Indonesia, owing to the largest mangrove cover in the world, has approximately 3.14 PgC stored in the mangroves, or about 33% of all carbon stored in coastal ecosystems globally. Unfortunately, our comprehensive understanding of carbon flux is hampered by the incomplete repertoire of field measurement data, especially from mangrove ecosystem-rich regions such as Indonesia and Asia Pacific. This study fills the gap in greenhouse gases (GHGs) flux studies in mangrove ecosystems in Indonesia by quantifying the soil CO2 and CH4 fluxes for different land use types in mangrove ecosystems, i.e., secondary mangrove (SM), restored mangrove (RM), pond embankment (PE) and active aquaculture pond (AP). Environmental parameters such as soil pore salinity, soil pore water pH, soil temperature, air temperature, air humidity and rainfall are also measured. Results GHG fluxes characteristics varied between land use types and ecological conditions. Secondary mangrove and exposed pond embankment are potential GHG flux sources (68.9 ± 7.0 and 58.5 ± 6.2 MgCO2e ha− 1 yr− 1, respectively). Aquaculture pond exhibits the lowest GHG fluxes among other land use types due to constant inundation that serve as a barrier for the release of GHG fluxes to the atmosphere. We found weak relationships between soil CO2 and CH4 fluxes and environmental parameters. Conclusions The data and information on GHG fluxes from different land use types in the mangrove ecosystem will be of importance to accurately assess the potential of the mangrove ecosystem to sequester and emit GHGs. This will support the GHG emission reduction target and strategy that had been set up by the Indonesian Government in its Nationally Determined Contributions (NDC) and Indonesia’s 2030 Forest and Other Land Use (FOLU) Net Sink.

Seagrass meadows serve as vital blue carbon ecosystems, sequestering significant amounts of CO2 and playing a crucial role in climate change mitigation. Semujur Island, located in the Bangka Belitung Province, exemplifies numerous small Indonesian islands boasting extensive seagrass meadows lining their shores. This research seeks to (1) describe the community structure of seagrass on Semujur Island, (2) assess the carbon storage within the seagrass ecosystem, and (3) analyze the relationship between seagrass community structure and carbon reserves across three distinct sites. According to the results of this study, there are eight species of seagrass on Semujur Island, i.e., Cymodocea rotundata, Enhalus acoroides, Halodule uninervis, Halophila ovalis, Oceana serrulata, Syringodium isoetifolium, Thalassia hemprichii, and Thalassodendron ciliatum. Diversity indices varied among sites, ranging from 1.48 to 1.72. Species evenness indices varied between 0.83 and 0.92, while dominance indices varied between 0.20 and 0.28. The highest estimated carbon stock was obtained at the site dominated by the species H. uninervis (75.11 MgC/ha); followed by the site dominated by T. hemprichii (50.55 MgC/ha). The correlation between seagrass community structure, including density and coverage, and carbon stocks demonstrated a moderate positive correlation, with coefficients of 0.430 and 0.528, respectively (p

Societal Impact Statement Seagrass ecosystems are of fundamental importance to our planet and wellbeing. Seagrasses are marine flowering plants, which engineer ecosystems that provide a multitude of ecosystem services, for example, blue foods and carbon sequestration. Seagrass ecosystems have largely been degraded across much of their global range. There is now increasing interest in the conservation and restoration of these systems, particularly in the context of the climate emergency and the biodiversity crisis. The collation of 100 questions from experts across Europe could, if answered, improve our ability to conserve and restore these systems by facilitating a fundamental shift in the success of such work. Summary Seagrass meadows provide numerous ecosystem services including biodiversity, coastal protection, and carbon sequestration. In Europe, seagrasses can be found in shallow sheltered waters along coastlines, in estuaries & lagoons, and around islands, but their distribution has declined. Factors such as poor water quality, coastal modification, mechanical damage, overfishing, land‐sea interactions, climate change and disease have reduced the coverage of Europe’s seagrasses necessitating their recovery. Research, monitoring and conservation efforts on seagrass ecosystems in Europe are mostly uncoordinated and biased towards certain species and regions, resulting in inadequate delivery of critical information for their management. Here, we aim to identify the 100 priority questions, that if addressed would strongly advance seagrass monitoring, research and conservation in Europe. Using a Delphi method, researchers, practitioners, and policymakers with seagrass experience from across Europe and with diverse seagrass expertise participated in the process that involved the formulation of research questions, a voting process and an online workshop to identify the final list of the 100 questions. The final list of questions covers areas across nine themes: Biodiversity & Ecology; Ecosystem services; Blue carbon; Fishery support; Drivers, Threats, Resilience & Response; Monitoring & Assessment; Conservation & Restoration; Governance, Policy & Management; and Communication. Answering these questions will fill current knowledge gaps and place European seagrass onto a positive trajectory of recovery.

Salt marshes provide many important ecosystem services, key among them being carbon sequestration. However, a large degree of uncertainty remains in salt marsh carbon budgets, particularly during colder months of the year when salt marsh microbial and vegetative activity is assumed to dormant. We also lack data on urban systems. In this study, we used an easily portable carbon dioxide sensor package to directly measure net carbon dioxide (CO2) fluxes throughout the winter in a temperate, urban salt marsh. We sampled across the dormant season both on normal (cold) temperature days and on days that were anomalously warm (defined here as air temperatures 2.8°C above the long-term average). We demonstrated that median (±mad) daytime CO2 fluxes doubled on the warm days, compared to cold days (1.7 ± 2 mmol m-2 h-1, 0.7 ± 1.3 mmol m-2 h-1, respectively). We also show that net CO2 emissions scaled with soil temperature. The high day-to-day variability, however, implies that infrequent or sparse measurements cannot sufficiently capture the temporal dynamics of dormant season salt marsh net CO2 fluxes. The magnitude of the net CO2 source from our sampling during the dormant season leads us to hypothesize that, as mean annual temperatures continue to increase, dormant season CO2 emissions from salt marshes will increasingly offset growing season carbon dioxide uptake. This change compromises the carbon sequestration capacity, and therefore the climate mitigation potential of these ecosystems. Future studies should focus on quantifying the impact of dormant season CO2, and other greenhouse gases on salt marsh carbon budgets. [ABSTRACT FROM AUTHOR]

Monitoring mangrove forest biomass is vital for assessing their carbon sequestration potential. This study uses airborne LiDAR data to estimate the aboveground biomass (AGB) of an old‐growth mangrove forest in the Katunggan It Ibajay Ecopark (KII Ecopark) on Panay Island, Philippines. To establish a relationship between the LiDAR canopy height profile with the field observed AGB at the plot level, we tested 20 LiDAR derived relative height (RH) metrics. First, we tested a relationship between field observed Lorey's mean canopy height (Hm) and RH metrics, which were then used to estimate AGB by applying a previously established allometric model. Second, we tested the direct relationship between RH metrics and observed AGB. Among RH metrics, RH95 showed the best correspondence with the Hm (R2 = 0.79) and when it was applied to the previously developed allometric for AGB estimation, the results showed a large underestimation of AGB (R2 = 0.46) for plots with higher canopy heights. Conversely, the direct method using a power regression model with RH95 and observed AGB provided a better estimate (R2 = 0.58). However, both models still underestimated AGB at the KII Ecopark. We conclude that, LiDAR‐based AGB estimation using Hm as a single variable can result in considerable underestimation, especially in old‐growth mangrove forests such as KII Ecopark. Further studies are necessary to develop accurate models for estimating AGB in such special types of mangroves which is important for mangrove monitoring, reporting and verification (MRV). [ABSTRACT FROM AUTHOR]

Blue Carbon is increasingly popular worldwide, and it also belongs to circular economy field which would last a long period in academy. To further understand the development and characteristics of Blue Carbon, this study uses CiteSpace software to perform quantitative analysis on literature published on Web of Science and Chinese CNKI database with the main topic of "Blue Carbon." The results show that: (1) Since 2009, increasing attention has been paid to Blue Carbon research, among which the United States, Australia and China are the leading countries. (2) Keywords such as "Blue Carbon," "mangrove," "carbon sequestration" and "carbon neutrality" are the high-frequency keywords appearing both in China and the World in recent years. (3) Spartina alterniflora, soil organic carbon, livestock, trophic cascade, biodiversity and seagrass ecosystem clustering are hot topics related to international Blue Carbon research, while organic carbon, seagrass-conservation, methodology, sustainable development, climate change, carbon neutralization, coastal zone and carbon storage are hot topics related to Chinese Blue Carbon research. In addition, based on the research trends of Blue Carbon, this paper attempts to sort out the research framework from three levels: core characteristics, theoretical basis and research methods, respectively. Facing a series of challenges brought by climate change, Blue Carbon research should strengthen the accurate estimations of Blue Carbon sink and its market potential, and explore the reasonable market mechanism and protection mechanism, to respond to realistic demands, solve major concerns and promote new progress in Blue Carbon theory and practice. [ABSTRACT FROM AUTHOR]

Rahim, A.; Soeprobowati, T.R.; Putranto, T.T.; Hadiyanto, H., and Alfalah, M.H., 2024. Investigating the impact of climate and land use changes on mangrove ecosystems: A bibliometric analysis from 2013 to 2023. Journal of Coastal Research, 40(4), 768–778. Charlotte (North Carolina), ISSN 0749-0208. Mangroves are essential to the stability of coastal regions, especially when facing the threat of climate change. However, deforestation, land use changes, and rising sea levels destroy mangrove forests. Based on bibliometric analysis, this paper aims to gain insight into the impact of climate and land use changes on mangroves. By searching Scopus, 534 pieces of literature from 2013 to 2023 were found, and they were analyzed based on bibliometric information and article metadata. Trends and hotspots of the impact of climate and land use changes on mangrove research were explored using VOSviewer software. The results of a network co-occurrence analysis revealed that mangroves, climate change, land use change, blue carbon, and wetlands represent the most popular central areas of study. The results of this paper show that the countries with the greatest number of publications on mangroves and climate and land use changes are the United States, Australia, India, Indonesia, and China. The research findings revealed that remote sensing and geographic information systems (GIS) are the most recently used technologies to enhance the research field of ecosystem monitoring in mangrove research. Maintaining and increasing carbon sinks through sustainable management of mangrove ecosystems have been a potential priority in climate change and mangrove ecosystem research development. This research highlights trends in the impact of climate and land use changes on mangrove ecosystem research over the past 10 years. It identifies areas that require further research investment to promote future research collaboration. [ABSTRACT FROM AUTHOR]

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The climate benefit of blue carbon sequestered by mangrove forests can be partially offset by CH4 emission, but this offset is rarely assessed using multi‐year high‐frequency measurements. Here, four‐year eddy covariance measurements were used to examine temporal patterns of CH4 flux and its blue carbon offset (i.e., reduced climate benefit) in a subtropical estuarine mangrove in China. We found both diel and seasonal CH4 fluxes were mainly driven by soil temperature and tidal activities, showing greater nighttime emission. On average, one‐tenth of CO2 uptake was offset by CH4 emission using the sustained‐flux global warming potential metric at a 20‐year time horizon, while this offset could vary over an order of magnitude due to asynchronous fluxes of CH4 and CO2 across diel and seasonal cycles. These results highlight the significant contribution of nighttime emission to mangrove CH4 budget and the importance of asynchronous flux variations in assessing mangrove's climate benefit. Plain Language Summary: Mangrove forests also emit CH4 into besides absorbing CO2 from the atmosphere, leading to reduced climate benefit of blue carbon sequestration or "blue carbon offset". To assess the temporal patterns of mangrove CH4 flux and blue carbon offset, we analyzed a four‐year time series of high‐frequency measurements of CH4 and CO2 fluxes in a subtropical estuarine mangrove in China. The results showed mangrove forests emitted more CH4 at night than in the daytime and the temporal variability of CH4 flux was co‐regulated by soil temperature and tidal activities. Mangrove CH4 emission on average offset one‐tenth of blue carbon sequestration based on the sustained‐flux global warming potential metric at a 20‐year time horizon, while this offset varied over an order of magnitude across time scales. Future studies on mangrove CH4 budget and climate benefit should pay more attentions to nighttime emission and the asynchronous variability between CH4 and CO2 fluxes. Key Points: Four‐year eddy covariance mangrove CH4 and CO2 fluxes were presented to examine temporal patterns of CH4 flux and its blue carbon offsetBoth diel and seasonal CH4 fluxes were mainly driven by soil temperature and tidal activities with greater nighttime emissionThe blue carbon offset by CH4 emission varied significantly across time scales due to asynchronous CH4 and CO2 flux variations [ABSTRACT FROM AUTHOR]

Climate change is reshaping coastal wetlands worldwide, driving ecosystem shifts like mangrove poleward expansion into saltmarshes in tropical‐temperate transitional zones. Though warming is recognized as the primary driver, a lack of detailed field studies limits our ability to predict mangrove responses to rapid climate warming.Here, we characterized how mangroves vary across a temperature gradient at 18 sites along Florida's Gulf of Mexico coast (USA). We used minimum air temperature (Tmin) derived from daily data from 1989 to 2021 as the independent variable and applied plot‐based and synoptic approaches to quantify species‐specific mangrove variation at community, population, and individual levels. We then used these results to spatially project future mangrove ecosystem properties under multiple warming scenarios.Across the Tmin gradient from −10.8 to −1.4°C, mangrove canopy height and coverage ranged from 0.4 to 11.5 m and 15% to 98%, respectively, with both exhibiting sigmoidal increases with Tmin. Estimated mangrove aboveground biomass ranged from 0 to 496.7 Mg/ha and showed a positive linear relationship with Tmin due both to the tall tree stratum's increased biomass per tree and higher abundance.While the population abundance and coverage of Rhizophora mangle and Laguncularia racemosa had positive linear relationships with Tmin, Avicennia germinans exhibited a significant quadratic relationship, reflecting the higher freeze tolerance of this species. Such tolerance may stem from A. germinans' higher morphological plasticity observed at the individual level, adapting to cold stress by exhibiting a more shrub‐like architecture at colder sites.Based on these field‐derived quantitative relationships, we projected substantial increases in mangrove coverage and canopy height near current range limits, with tall A. germinans dominating in the north and R. mangle dominating the centre and south of the study region.Synthesis. To better predict the ecological consequences in coastal wetlands under future climate change, it is essential to understand how mangroves respond to winter temperature regimes across a temperature gradient. Collectively, these cross‐level and species‐specific results advance our understanding of mangrove temperature sensitivity and provide information about the future of coastal wetland structure and function in response to a changing climate. [ABSTRACT FROM AUTHOR]

Background: Mangrove ecosystems exhibit significant carbon storage and sequestration. Its capacity to store and sequester significant amounts of carbon makes this ecosystem very important for climate change mitigation. Indonesia, owing to the largest mangrove cover in the world, has approximately 3.14 PgC stored in the mangroves, or about 33% of all carbon stored in coastal ecosystems globally. Unfortunately, our comprehensive understanding of carbon flux is hampered by the incomplete repertoire of field measurement data, especially from mangrove ecosystem-rich regions such as Indonesia and Asia Pacific. This study fills the gap in greenhouse gases (GHGs) flux studies in mangrove ecosystems in Indonesia by quantifying the soil CO2 and CH4 fluxes for different land use types in mangrove ecosystems, i.e., secondary mangrove (SM), restored mangrove (RM), pond embankment (PE) and active aquaculture pond (AP). Environmental parameters such as soil pore salinity, soil pore water pH, soil temperature, air temperature, air humidity and rainfall are also measured. Results: GHG fluxes characteristics varied between land use types and ecological conditions. Secondary mangrove and exposed pond embankment are potential GHG flux sources (68.9 ± 7.0 and 58.5 ± 6.2 MgCO2e ha− 1 yr− 1, respectively). Aquaculture pond exhibits the lowest GHG fluxes among other land use types due to constant inundation that serve as a barrier for the release of GHG fluxes to the atmosphere. We found weak relationships between soil CO2 and CH4 fluxes and environmental parameters. Conclusions: The data and information on GHG fluxes from different land use types in the mangrove ecosystem will be of importance to accurately assess the potential of the mangrove ecosystem to sequester and emit GHGs. This will support the GHG emission reduction target and strategy that had been set up by the Indonesian Government in its Nationally Determined Contributions (NDC) and Indonesia's 2030 Forest and Other Land Use (FOLU) Net Sink. [ABSTRACT FROM AUTHOR]

Mangrove soils are highly enriched in organic carbon. Tidal pumping drives seawater and oxygen into mangrove soils during flood tide and releases carbon-rich porewater during ebb tides. Here, we resolve semi-diurnal (flood/ebb tides), diel (day/night) and weekly (neap/spring tides) drivers of porewater-derived CO 2 fluxes in two mangroves and update global estimates of CO 2 emissions building on earlier observations from other sites. Tidal pumping controlled p CO 2 variability within the two mangrove creeks. The highest values of p CO 2 (2,585–6,856 µatm) and 222Rn (2,315–6,159 dpm m−3) and lowest values of pH (6.8–7.1) and dissolved oxygen (1.7–3.7 mg L−1) at low tides were due to enhanced porewater export. 222Rn and p CO 2 in mangrove porewater were 4–15 and 38–41 times greater than surface waters, respectively. p CO 2 increased by 50 ± 30 % from high to low tide, 9 ± 22 % from day to night and 57 ± 5 % from neap to spring tide with clear changes in hourly, diel, and weekly time scales. Combining our new estimates with literature data, global porewater-derived (16 sites) and water-atmosphere (52 sites) CO 2 fluxes in mangroves would upscale to 45 ± 12 and 41 ± 10 Tg C y−1, respectively. These fluxes represent 25 % of net primary production and are twice as high as the sediment carbon burial rates in global mangroves. Overall, our local observations and global compilation suggest that porewater-derived CO 2 exchange is a major but often unaccounted source of CO 2 in mangroves. The porewater-derived CO 2 can be emitted to the atmosphere or laterally exported to the ocean and should be included in carbon budgets to solve global imbalances. [ABSTRACT FROM AUTHOR]

Restoration of mangrove forests has garnered increasing global prominence as a nature‐based solution for carbon (C) sequestration. However, it was unclear whether the radiation forcing induced by methane (CH4) emissions and albedo changes during mangrove restoration processes can offset the cooling effect resulting from the net carbon dioxide (CO2) uptake. In this study, we measured the CO2, CH4, and albedo during 2020–2022 using an open‐path eddy covariance system in an 8‐year restored mangrove ecosystem afforested in Zhejiang Province, China. Their integrated global warming potentials (GWPs) were calculated to assess the climatic impact of mangrove restoration. The results showed that the restored mangroves functioned as a CO2 sink and a CH4 source, with annual values of −656.75 to −465.41 and 5.54 to 9.07 g C m−2 yr−1, respectively. The albedo varied slightly with a range of 0.11–0.13. The integrated GWPs of CO2, CH4, and albedo were −1,354.00 and −1,875.70 g CO2‐eq m−2 yr−1 over the 20‐ and 100‐year time horizons, respectively. The negative values indicated that the mangrove restoration had a net cooling effect, mainly due to CO2 uptake. The warming effects caused by CH4 emissions and albedo changes had the potential to partially offset CO2 uptake by 12.55%–36.51% and 0.08%–0.42%, respectively. Random forest analysis showed that photosynthetically active radiation (PAR) was the dominant driver on integrated GWPs with feature importance values of 0.34. Our results revealed that the cooling benefit of 8‐year restored mangroves remained significant, even when it was partially offset by CH4 emissions and albedo changes. Plain Language Summary: Restored mangrove ecosystems have great potential to mitigate climate change and expand natural carbon sinks. They have climate benefits by sequestering atmospheric carbon dioxide, but these benefits could be offset by methane emissions and albedo changes during mangrove restoration processes. Currently, long‐term measurements of these carbon fluxes and albedo in mangrove restoration are lacking. Based on 3‐year flux tower measurements, we examined these fluxes in 8‐year restored mangrove wetlands, located in the estuary of the Aojiang River in southeastern China. The mangrove restoration acted as a carbon dioxide sink and a methane source, and the albedo of the ecosystem exhibited slight variations of 0.11–0.13. The global warming potentials of these carbon fluxes and albedo were calculated to evaluate the climatic effect of mangrove restoration. The results showed that the cooling effect of carbon dioxide uptake was dominant in the restored mangrove ecosystem, partially offset by positive radiative forcing from methane emissions and albedo changes. Mangrove restoration resulted in a net cooling contribution to the climate, despite only 8 years of restoration. Key Points: Mangrove restoration acted as a CO2 sink and a CH4 source from 2020 to 2022Integrated GWPs of CO2, CH4, and albedo showed a net cooling effect in restored mangroves and were mainly driven by CO2 uptakeRandom forest algorithm showed that PAR was the most important driver of the integrated GWPs in the restored mangrove ecosystem [ABSTRACT FROM AUTHOR]

In salt marshes of the Southeastern USA, purple marsh crabs (Sesarma reticulatum), hereafter Sesarma, aggregate in grazing and burrowing fronts at the heads of tidal creeks, accelerating creek incision into marsh platforms. We explored the effects of this keystone grazer and sediment engineer on salt marsh sediment accumulation, hydrology, and carbon (C) and nitrogen (N) turnover using radionuclides (210Pb and 7Be), total hydrolyzable amino acids (THAA), and C and N stable isotopes (δ13C and δ15N) in sediment from paired Sesarma-grazed and un-grazed creeks. Sesarma-grazed-creek sediments exhibited greater bioturbation and tidal inundation compared to sediments in un-grazed creeks, as indicated by larger 210Pb and 7Be inventories. Total organic carbon (TOC) to total nitrogen (TN) weight ratios (C:N) were higher and δ15N values were lower in grazed-creek sediments than in un-grazed-creek sediments, suggesting Sesarma remove and assimilate N in their tissues, and excrete N with lower δ15N values into sediments. In support of this inference, the percent total carbon (TC) and percent TOC declined by nearly half, percent TN decreased by ~ 80%, and the C:N ratio exhibited a ~ threefold increase between Sesarma fore-gut and hind-gut contents. An estimated 91% of Sesarma's diet was derived from Spartina alterniflora, the region's dominant salt marsh plant. We found that, as Sesarma grazing fronts progress across marsh landscapes, they enhance the decay of Spartina-derived organic matter and prolong marsh tidal inundation. These findings highlight the need to better account for the effects of keystone grazers and sediment engineers, like Sesarma, in estimates of the stability and size of blue C stores in coastal wetlands. [ABSTRACT FROM AUTHOR]

The enormous soil carbon pool stored by mangroves depends upon microbial respiratory activities and enzymes associated with carbon breakdown in soils. Our hypothesis is that increased microbial activity leads to elevated carbon breakdown. To prove this, we measured microbial respiratory and enzyme activity for nitrogen, phosphorus, and carbon cycle in soil from three coastal ecosystems: mangroves, restinga, and Atlantic forest. The multivariate ordination analysis showed that each treatment had distinct soil microbial activity according to the soil layer and seasons. Our results suggest that the Atlantic forest ecosystem had the highest respiration activity (i.e., CO2-C release), dehydrogenase, phosphatase, protease, and urease activities, while mangroves and sandy coastal plains (called restinga) had lower respiration and enzyme activity. Therefore, soil microbial respiratory activity variation was influenced by soil microbial activity in the most superficial layer in coastal soil ecosystems. The agreement between dehydrogenase activity and CO2-C respiration measurements suggests that microbial activity is an efficient indicator of carbon breakdown. Our findings also indicate that the vegetation type in the different ecosystems contribute to stimulate the soil microbiota increasing both its microbial activity and carbon storage. These issues should be considered for the conservation policies to promote effective protection of vital coastal ecosystems in Brazil. Understanding the coastal ecosystem-induced nutrient shifts in microbial communities is important because they can lead to lagged and multiplicative effects on carbon storage. Taken together, our results illustrate the identification of keystone (organic carbon and microbial activity) as an indicator to offer evidence-providing tools to achieve more ecologically efficient managing practices. [ABSTRACT FROM AUTHOR]

Seagrasses are globally acknowledged as crucial habitats as they provide a variety of ecosystem services. Mexico's legislation protects most of these marine plants; however, the protection often fails in application. The Gulf of California, despite being a biodiversity hotspot, has scant data on seagrasses. Here, human activity and climate change increasingly threaten these coastal ecosystems, with conservation and research efforts lacking coordination at a regional level. Our manuscript aimed to review and standardize existing data on Gulf of California seagrass species, ensuring open access for data updates; pinpointing conservation deficiencies; and guiding future research. We have added new records to the official public data, but we were able to recapture only 25% of the seagrass locations meaning a potential reduction in their historical distribution of 45.8%. Even though Mexico's legislation protects some species of seagrasses, it protection often fails in the application. We identified that only 6.1% of the seagrass locations are within protected areas that recognize their presence in their management plans (e.g., the Balandra Flora and Fauna Protected Area and the Upper Gulf of California and Colorado River Delta Biosphere Reserve). At least 55.9% of seagrass records are associated with potentially damaging activities like pollution, coastal modification or biological resources use, while 23% are exposed to higher frequency of marine heatwaves. Given the importance of seagrass meadows under Mexican law and their internationally recognized ecological value, sharing current information and guiding research is essential. Our study seeks to galvanize renewed research initiatives and raise more awareness on the conservation of the Gulf of California's seagrasses. [ABSTRACT FROM AUTHOR]