Blue Carbon Ecosystems Research Articles

Alkalinity export to the ocean is a major carbon sequestration mechanism in a macrotidal saltmarsh

AbstractSaltmarshes are a blue carbon ecosystem accumulating large quantities of organic carbon in sediments. Some of this carbon can be transformed into dissolved inorganic carbon (DIC) and methane (CH4) that may eventually be exported to the ocean or atmosphere. Although extensive studies have quantified specific components of the carbon budget such as carbon burial, limited attention has been given to pore‐water‐derived carbon and total alkalinity (TA) exports to the ocean. Here, we quantified lateral exports to the ocean (outwelling) of 202 ± 160 and 78 ± 75 mmol m−2 d−1 of DIC and TA, respectively. The TA : DIC concentration ratio in the creek waters was ~ 1, implying TA production from anaerobic mineralization in sediments. The lateral TA exports were comparable to the local (94 ± 48 mmol m−2 d−1) and national (~ 50 mmol m−2 d−1) organic carbon burial. High TA exports could locally increase the ocean buffering capacity and contribute bicarbonate to the coastal ocean, acting as a long‐term carbon storage. Pore water traced by radon contributed 28–37% and 58–69% of DIC and TA exports. Separating the two major DIC components (i.e., CO2 emissions and alkalinity exports) is essential to resolve the carbon sequestration potential from saltmarshes. Here, dissolved CO2 emissions to the atmosphere accounted for 3–5% of total DIC outwelling. CH4 emissions played a minor role offsetting around 0.3 to 6% of the carbon sequestration. Overall, we demonstrate that alkalinity export into the ocean can be an overlooked carbon sequestration pathway in saltmarshes at rates comparable to carbon burial.

Towards Incorporation of Blue Carbon in Falkland Islands Marine Spatial Planning: A Multi-Tiered Approach

Ecosystem-based conservation that includes carbon sinks, alongside a linked carbon credit system, as part of a nature-based solution to combating climate change, could help reduce greenhouse gas levels and therefore the impact of their emissions. Blue carbon habitats and pathways can also facilitate biodiversity retention, aiding sustainable fisheries and island economies. However, robust blue carbon research is often limited at the scale of regional governance and management, lacking both incentives and facilitation of policy-integration. The remote and highly biodiverse coastal ecosystems and surrounding continental shelf can be used to better inform long-term ecosystem-based management in the vast South Atlantic Ocean and sub-Antarctic, to synergistically protect both unique biodiversity and inform on the magnitude of nature-based benefits they provide. Understanding key ecosystem information such as their location, extent, and condition of habitat types, will be critical in understanding carbon pathways to sequestration, threats to this, and vulnerability. This paper considers the current status of blue carbon data and information available, and what is still required before blue carbon can be used as a conservation management tool integrated in national Marine Spatial Planning (MSP) initiatives. Our research indicates that the data and information gathered has enabled baselines for a number of different blue carbon ecosystems, and indicated potential threats and vulnerability that need to be managed. However, significant knowledge gaps remain across habitats, such as salt marsh, mudflats and the mesophotic zones, which hinders meaningful progress on the ground where it is needed most.

Resilient consumers accelerate the plant decomposition in a naturally acidified seagrass ecosystem.

Anthropogenic stressors are predicted to alter biodiversity and ecosystem functioning worldwide. However, scaling up from species to ecosystem responses poses a challenge, as species and functional groups can exhibit different capacities to adapt, acclimate, and compensate under changing environments. We used a naturally acidified seagrass ecosystem (the endemic Mediterranean Posidonia oceanica) as a model system to examine how ocean acidification (OA) modifies the community structure and functioning of plant detritivores, which play vital roles in the coastal nutrient cycling and food web dynamics. In seagrass beds associated with volcanic CO2 vents (Ischia, Italy), we quantified the effects of OA on seagrass decomposition by deploying litterbags in three distinct pH zones (i.e., ambient, low, extreme low pH), which differed in the mean and variability of seawater pH. We replicated the study in two discrete vents for 117 days (litterbags sampled on day 5, 10, 28, 55, and 117). Acidification reduced seagrass detritivore richness and diversity through the loss of less abundant, pH-sensitive species but increased the abundance of the dominant detritivore (amphipod Gammarella fucicola). Such compensatory shifts in species abundance caused more than a threefold increase in the total detritivore abundance in lower pH zones. These community changes were associated with increased consumption (52%-112%) and decay of seagrass detritus (up to 67% faster decomposition rate for the slow-decaying, refractory detrital pool) under acidification. Seagrass detritus deployed in acidified zones showed increased N content and decreased C:N ratio, indicating that altered microbial activities under OA may have affected the decay process. The findings suggest that OA could restructure consumer assemblages and modify plant decomposition in blue carbon ecosystems, which may have important implications for carbon sequestration, nutrient recycling, and trophic transfer. Our study highlights the importance of within-community response variability and compensatory processes in modulating ecosystem functions under extreme global change scenarios.

Effects of oyster aquaculture on carbon capture and removal in a tropical mangrove lagoon in southwestern Taiwan

Blue carbon ecosystems (BCEs) are a promising resource for the mitigation of global warming; however, climate spectrums and anthropogenic activities could influence the fragile balance of BCEs as carbon sinks or sources. We assess how oyster farming affects dissolved inorganic carbon (DIC) and total alkalinity (TA) on CO2 fluxes in a mangrove-dominated lagoon. Water physical, chemical and biological parameters were recorded by in-situ buoys within the lagoon and at its inflow. Structural equation modeling was adopted to clarify the factors/processes controlling the partial pressure of CO2 (pCO2). A three-dimensional environmental model followed by a conceptual DIC model was used to quantify the spatiotemporal patterns of capture and release of DIC and TA by oyster production. The results showed that 49% of TA and DIC released from mangroves was depleted by oyster shell formation. DIC was reduced by algal photosynthesis and algal was served as a food source supporting oyster production. Annual oyster production through phytoplankton photosynthesis accounted for 11% of the atmosphere carbon inflows, suggesting that oyster production served as a significant atmospheric/terrestrial carbon sink in the lagoon. The results indicate that mangroves benefit local oyster production by acting as an important source of DIC and TA, and that the oyster aquaculture contributed to carbon capture in a mangrove-dominated lagoon ecosystem.

Continental-scale plant invasions reshuffle the soil microbiome of blue carbon ecosystems.

Theory and experiments support that plant invasions largely impact aboveground biodiversity and function. Yet, much less is known on the influence of plant invasions on the structure and function of the soil microbiome of coastal wetlands, one of the largest major reservoirs of biodiversity and carbon on Earth. We studied the continental-scale invasion of Spartina alterniflora across 2451 km of Chinese coastlines as our model-system and found that S. alterniflora invasion can largely influence the soil microbiome (across six depths from 0 to 100 cm), compared with the most common microhabitat found before invasion (mudflats, Mud). In detail, S. alterniflora invasion was not only positively associated with bacterial richness but also resulted in important biotic homogenization of bacterial communities, suggesting that plant invasion can lead to important continental scale trade-offs in the soil microbiome. We found that plant invasion changed the community composition of soil bacterial communities across the soil profile. Moreover, the bacterial communities associated with S. alterniflora invasions where less responsive to climatic changes than those in native Mud microhabitats, suggesting that these new microbial communities might become more dominant under climate change. Plant invasion also resulted in important reductions in the complexity and stability of microbial networks, decoupling the associations between microbes and carbon pools. Taken together, our results indicated that plant invasions can largely influence the microbiome of coastal wetlands at the scale of China, representing the first continental-scale example on how plant invasions can reshuffle the soil microbiome, with consequences for the myriad of functions that they support.

New possibilities for climate change countermeasures in ports: Organic carbon containment and creation of blue carbon ecosystems through beneficial utilization of dredged soil

As climate change has attracted increasing global attention, carbon neutral ports (CNPs) have been set as government policies in Japan. In this research, with the aim of providing a more reliable basis for policy making concerning ports, we proposed the carbon storage through stable containment of organic carbon present in dredged soil as a new climate change countermeasure in ports. Furthermore, it was revealed through scenario analysis that the containment effect through beneficial utilization of dredged soil as foundation materials for blue carbon ecosystems (BCEs) and carbon storage by BCEs have significant meanings for the realization of CNPs and sinks for the residual emissions, considering the necessity to promote dredging projects for the development of the next generation of import bases toward the realization of CNPs, which may result in the generation of a large amount of dredged soil. In a country like Japan, whose port policies and port governance make it difficult to actively promote climate change countermeasures by each port, the feasibility of these new countermeasures would depend on the government’s initiative. It would be a world-leading effort to focus on port development in addition to port operation, and utilizing the dredged soil and BCEs as carbon sinks.

Integrating blue: How do we make nationally determined contributions work for both blue carbon and local coastal communities?

Blue Carbon Ecosystems (BCEs) help mitigate and adapt to climate change but their integration into policy, such as Nationally Determined Contributions (NDCs), remains underdeveloped. Most BCE conservation requires community engagement, hence community-scale projects must be nested within the implementation of NDCs without compromising livelihoods or social justice. Thirty-three experts, drawn from academia, project development and policy, each developed ten key questions for consideration on how to achieve this. These questions were distilled into ten themes, ranked in order of importance, giving three broad categories of people, policy & finance, and science & technology. Critical considerations for success include the need for genuine participation by communities, inclusive project governance, integration of local work into national policies and practices, sustaining livelihoods and income (for example through the voluntary carbon market and/or national Payment for Ecosystem Services and other types of financial compensation schemes) and simplification of carbon accounting and verification methodologies to lower barriers to entry.

Dissolved Iron from Steel Slag with Its Chelating Agent Promotes Seaweed Growth

Blue carbon ecosystems are crucial for carbon sequestration on a global scale. However, it is unclear how we could promote and maximize carbon sequestration. Here, we demonstrate that providing an iron source to seaweed fostered its growth through increased photosynthetic efficiency and transformed the carbon into a biomass. Firstly, we revealed that the mixture of the steel slag and DTPA eluted iron dramatically in seawater. Next, we applied the eluate of the slag-DTPA pellet to the seaweed. The results for the eluate treatment showed a 25.8% increase in the photosynthetic pigment level and a 44.9% increase in the seaweed weight. Furthermore, we confirmed no elution of potential toxic substances from the steel slag and DTPA pellet. Finally, we applied the pellet at a depth of 15 m near seaweeds and observed a 52.0% increase of carbon weight in the pellet treated group, while the non-treated group showed only a 10.3% increase for five months. This study indicated that steel slag-DTPA pellet treatment induced seaweed growth and efficiently transformed its carbon into a seaweed biomass. Thus, steel slag and its chelating agent may contribute to the promotion of sea forestation and a subsequent increase in carbon sequestration known as blue carbon.

Blue Carbon Ecosystems in Brazil: Overview and an Urgent Call for Conservation and Restoration

In this article, we discuss knowledge and gaps regarding blue carbon ecosystems (BCEs) in Brazil, considering the urgency to apply protection actions and policies to safeguard their biodiversity and associated ecosystem services. We also indicate areas of further research to improve carbon stocks and sequestration rate estimates. We call attention to the shortage of studies on Brazilian BCEs relative to the growing knowledge on the Blue Carbon Framework accumulated worldwide over the last decade. Considering the extensive Brazilian Economic Exclusive Zone (known as “Blue Amazon”), knowledge concerning blue carbon stocks is vital at regional and global scales for mitigating global increases in atmospheric carbon dioxide (CO2). The Blue Amazon has at least 1,100,000 ha of vegetated and non-vegetated coastal ecosystems (mangroves, salt marshes, seagrass meadows, and hypersaline tidal flats) that collectively contain vast amounts of stored carbon, making Brazil an ideal place to test mechanisms for evaluating, conserving, and restoring BCEs. Other poorly understood potential sinks and sources of carbon are macroalgal and rhodolith beds, mudflats, continental shelf sediments, and marine animal forests in shallow, mesophotic, and deep waters. The carbon fluxes between diverse environmental compartments, such as soil–air, soil–water, groundwater–water–surface water, air–water, and land–ocean, in BCEs across the Blue Amazon must be studied. We emphasize the importance of assessing the total carbon stock and the recent dismantling of environmental laws that pose great risks to these important BCEs. The conservation and recovery of these areas would enhance the carbon sequestration capacity of the entire country. Furthermore, we highlight priorities to improve knowledge concerning BCEs and their biogeochemical cycles in the Blue Amazon and to provide information to assist in the reduction of atmospheric levels of CO2 for the United Nations Decade of Ocean Science (2021–2030).

Mapping seagrass meadows in coastal China using GEE

Seagrass meadows are virtual blue carbon ecosystems facing a dramatic decline on a global scale. Tracking the status and trends of seagrass meadows, which is still pending on large scales, is an emerging priority for their conservation and restoration. Here, we develop a semi-automatic procedure to identify and map seagrass meadows. Using Sentinel-2 data in Google Earth Engine (GEE) platform, a map is generated, showing a total of 11113.4 ha of seagrass meadows in coastal China in 2020. There exists the largest extent (6450.3 ha) in the coast of the South China Sea, while the second area (3909.5 ha) is in the Yellow Sea-Bohai Sea, and the seagrass meadows in the East China Sea cover about 753.6 ha. Our results provide the baseline data of seagrass meadows distribution in coastal China, and this study can be of reference for mapping seagrass meadows on a broader or even global scale.

“Slow” and “fast” in blue carbon: Differential turnover of allochthonous and autochthonous organic matter in minerogenic salt marsh sediments

AbstractSalt marshes are recognized as blue carbon ecosystems for their ability to rapidly sequester organic carbon (OC) via sedimentation. For this reason, there is growing interest in managing these systems to help mitigate climate change. However, in order for sediment accretion to offset ongoing CO2 emissions, organic matter undergoing burial must be derived from contemporary primary production. To investigate the provenance of OC sequestered by salt marshes, we analyzed the concentration and isotope composition (δ13C and Δ14C) of sedimentary OC in two minerogenic marshes in San Francisco Bay, California, USA. Data from the low marsh dominated by Spartinaspp. show that autochthonous OC is entering the sediment matrix and may in part be stabilized through incorporation into the mineral‐bound pool. However, the sedimentary OC stock as a whole is dominated by material with low values of δ13C (~ −20 to −25‰) and Δ14C (~ 100 to −300‰) indicating a preponderance of allochthonous OC that was retained in other OC reservoirs for 102 to 103 years prior to deposition in the marsh. Diagenetic modeling of OC and its δ13C values further shows that autochthonous OC is lost from the sediment profile at a much faster rate than allochthonous OC. The rapid turnover of contemporary autochthonous OC (“fast carbon”) relative to the apparent stability of old allochthonous OC (“slow carbon”) suggest that carbon burial at these sites is largely decoupled from ongoing CO2 emissions.

Evidence of improvements in the water quality of coastal areas around China

Coastal areas are huge carbon stores and hotspots for marine carbon fixation. Changes in the water quality of coastal areas are closely linked to their carbon fixation function. In this study, monitoring data were analyzed to identify how the water quality in China's coastal areas changed from 2001 to 2020. The results showed that the water quality in the coastal areas had improved gradually since 2001. The proportion of water quality in Class II and above gradually increased from 41.4% in 2001 to 77.4% in 2020, meanwhile, the proportion of water quality less than Class II, decreased from 58.6% to 22.6%, respectively. Of the four sea areas, the water quality was best in the Yellow Sea, and was poor in the East China Sea. The water quality varied between the different coastal provinces and cities and was good in coastal areas of Hainan, Guangxi, Shandong, and other provinces and cities, but was poor in Shanghai, Zhejiang, and Tianjin. Terrestrial anthropogenic pollutants were the main influence on the water quality in the coastal areas. As a hotspot for fixing blue carbon, the continuous improvement of the water quality of coastal areas laid a foundation for the health of the blue carbon ecosystems.

Research Development, Current Hotspots, and Future Directions of Blue Carbon: A Bibliometric Analysis

The blue carbon ecosystem has a strong capacity for carbon sequestration, but its research progress and development are still unclear. This study used CiteSpace to conduct a visual analysis, based on the analysis of 908 articles retrieved from the Web of Science Core Collection. The results showed that blue carbon research has gone through an early exploratory stage based on the scientific concept research, a research stage on the carbon sequestration process of the diverse blue carbon ecosystems, and a blue carbon protection and restoration stage based on climate change and human activities. The blue carbon theoretical framework has been continuously improved and the subject is currently more focused. The hot research topics are different at different stages. In the early stage, they focused on the types of blue carbon ecosystems and the process of carbon sequestration. Blue carbon research has developed from a single ecosystem type to multiple ecosystem types, and from concept recognition to system assessment research. Recently, research on the response, restoration and protection of blue carbon ecosystems has become a hotspot under the combined effect of human activities and climate change. In the future, it is necessary to strengthen the scientific research on blue carbon, to protect the integrity of the ecosystem structure and service functions, and to make a greater contribution to the global carbon neutrality strategy.

Beyond habitat boundaries: Organic matter cycling requires a system‐wide approach for accurate blue carbon accounting

AbstractAs coastal ecosystems become widely recognized for their capacity to sequester carbon (blue carbon), standard accounting methodologies for the generation of carbon credits are being developed. To ensure the applicability of these standards across blue carbon ecosystems, we investigated organic carbon provenance and burial in salt marshes and seagrass meadows of an arid, upwelling‐dominated Eastern Pacific lagoon. We found low carbon density in benthic sediments of Bahía de San Quintín (5.9 ± 0.5 mg C cm−3), only marginally higher in Zostera marina beds (6.9 ± 0.5 mg C cm−3), likely due to remineralization and hydrodynamically driven export of seagrass material, resulting in low carbon burial rates (4.5 ± 2.5 g C m−2 yr−1). Sediment organic carbon is mainly controlled by the fraction of fine sediment and its source is largely allochthonous, although sources differ spatially. Salt marshes at San Quintín derive 40% of their organic matter from autochthonous material and exhibit higher carbon burial rates (up to 414.7 ± 28.6 g C m−2 yr−1) and sediment carbon densities (32.0 ± 0.7 mg C cm−3) compared to benthic sediments. This study emphasizes the connectivity of blue carbon habitats with marsh plant detritus supplementing benthic carbon burial and incorporation of detrital eelgrass in marsh sediments. Our findings highlight the importance of allochthonous organic matter for carbon sequestration in blue carbon habitats, suggesting standard accounting practices that deduct allochthonous organic matter would miss the full potential for carbon burial.

Coastal Ecosystem Services Modeling in Latin America to Guide Conservation and Restoration Strategies: The Case of Mangroves in Guatemala and El Salvador

We modeled the coastal protection and blue carbon ecosystem services provided by the mangroves of the Paz River Basin (El Salvador and Guatemala) using InVEST Coastal Vulnerability and Coastal Blue Carbon Models, with the goal of supporting the Regional Coastal Biodiversity Project of the International Union for the Conservation of Nature, in determining potential priority mangrove areas for conservation and restoration. To quantify the relative coastal protection that mangroves provide, we combined maps of different aspects of vulnerability, including ecological, physical, and social data. We also estimated carbon stocks, net sequestration, and the economic value of carbon sequestration as a service in 2050 and 2100. We then developed a combined index of coastal protection and carbon sequestration services to highlight potential priority conservation and restoration areas for mangroves. We found that in Guatemala the coastal protection service was provided in greater quantity in the province of Moyuta, while in El Salvador this service was the highest in the provinces of San Francisco Menéndez, Jujutla and Acajutla, which also had the greatest total carbon stock. In the Paz River Basin, we estimate there are approximately 1,741 hectares of mangroves that provide the highest coastal protection and carbon sequestration services. Furthermore, we identified 318.9 hectares across both countries where mangroves could potentially be restored.

Evolution of blue carbon trading of China's marine ranching under the blue carbon special subsidy mechanism

The carbon sequestration function of marine ranching (MR) is an important part of the carbon cycle. China carrying out blue carbon trading (BCT) of MR will improve the carbon trading mechanism, protect the blue carbon ecosystem, and promote the realization of carbon neutrality. We construct an evolutionary game model comprising three players interacting under a mixed carbon policy, namely the Chinese local government, MR, and firms that demand blue carbon. We analyze four possible stable points and numerically simulate the main parameters such as the subsidy intensity, blue carbon price, and carbon tax standard, and discuss the evolution path of each player under the blue carbon special subsidy mechanism. We find that the local government providing special subsidies for BCT is essential for building a blue carbon market. Differentiated subsidies and taxes can be implemented for different types of MR to strengthen the carbon sequestration enthusiasm of MR. In the initial stage of BCT, the subsidized blue carbon price should be lower than the carbon tax standard; after building the blue carbon market, the subsidized blue carbon price can be adjusted to be the same as the carbon tax standard. Moreover, it is necessary to research and develop supporting management and monitoring facilities for MR to maintain the blue carbon ecosystem's stability and avoid the positive feedback effect of the carbon cycle.

Deposition Flux, Stocks of C, N, P, S, and Their Ecological Stoichiometry in Coastal Wetlands With Three Plant Covers

The depositional flux of coastal wetlands and the deposition rate of biogenic elements greatly affect the carbon sink storage. Ecological stoichiometry is an important ecological indicator, which can simply and intuitively indicate the biogeochemical cycle process of the region. This study investigated the soil deposition flux, stocks, and ecological stoichiometric ratios of C, N, P, and S under different water and salt conditions based on 137Cs dating technology in the Yellow River Delta (YRD) of China. The results showed that the deposition fluxes were 0.38 cm/year for PV wetlands, 1.08 cm/yr for PA wetlands, and 1.06 cm/yr for SS wetlands. Similarly, PA wetlands showed higher deposition fluxes of C, N, and S compared with SS and PV wetlands. PA wetlands had higher stocks of C (5.86 kg/m2), N (0.36 kg/m2) and S (0.36 kg/m2) in the top 1-m soil layer compared with PV and SS wetlands. However, the highest deposition rate of P (9.82 g/yr/m2) was observed in SS wetlands among the three wetlands. Three accumulative hotspots of C, N, and S in soil profiles of PA and SS wetlands were observed at soil depths of 0–10, 40–60, and 90–100 cm, whereas one accumulative hotspot of P was at the soil depth of 10–12 cm in SS wetlands and 80–82 cm in PA wetlands. PV wetlands showed higher accumulations of C, P, and S in the top 10 cm soil layer and N at the soil depth of 90–100 cm. The higher top concentration factors in these three wetlands indicated that the dominant input of plant residues was the main reason. The ratios of C/N and C/N/P of each sampling site were higher in the surface soils and decreased with depth. The ratios of C/P and N/P were larger in the surface layer (0–20 cm), the middle layer (40–60 cm), and the deep layer (90–100 cm). The ratios of N/P and C/N/P were relatively lower, indicating that these studied wetlands were N-limited ecosystems. The results implied that the coastal wetlands in the YRD have huge storage potential of biogenic elements as blue carbon ecosystems.

GETTING BY ANTHROPOCENE WITH A LITTLE HELP FROM MICROBES

When modern man evolved in Africa 250,000 years ago by hunting and gathering, would he dream of megalopolis and flying machines? Would he ever understand how we managed to create and expand so much that this could cause our very decline like an Icarus that reached for the sun while the wax on his wings melts? Nowadays, as we find more and more evidence of the negative impacts we have caused to the biosphere, we are also looking for solutions to write a different future, a sustainable future. In this perspective, I present how a microbcentric approach can help achieve many of the Sustainable Development Goals (SDGs) based on the knowledge that microorganisms are the engines of life on Earth. The science of microbiology has shown that most microorganisms are not pathogens but live in close association with almost any plant or animal, with many advantages that can certainly be used in an evidence-based manner. Each of the 17 SDGs can be strengthened by considering microbes – from improving or restoring soil fertility to produce food to protecting blue carbon ecosystems, such as corals and mangroves. Recognizing that these minuscule beings hold one of the keys to a sustainable future is essential, which would be achieved by strengthening research, microbial literacy actions, and cooperation among scientists, stakeholders, decision-makers, and society. Microorganisms can help us create opportunities for the future, like a Daedalus that finally gets heard by an arrogant Icarus.
 Keywords: Sustainable Development Goals, bioeconomy, microbial innovations, sustainability, climate change.

Temporal and spatial dynamics of tropical macroalgal contributions to blue carbon

Blue carbon ecosystems are a vital part of nature-based climate solutions due to their capacity to store and sequester carbon, but often exclude macroalgal beds even though they can form highly productive coastal ecosystems. Recent estimates of macroalgal contributions to global carbon sequestration are derived primarily from temperate kelp forests, while tropical macroalgal carbon stock in living biomass is still unclear. Here, using Singapore as a case study, we integrate field surveys and remote sensing data to estimate living macroalgal carbon stock. Results show that macroalgae in Singapore account for up to 650 Mg C biomass stock, which is greater than the aboveground carbon found in seagrass meadows but lower than that in mangrove forests. Ulva and Sargassum dominate macroalgal assemblages and biomass along the coast, with both genera exhibiting distinct spatio-temporal variation. The annual range of macroalgal biomass carbon is estimated to be 450 Mg C yr−1, or 0.77 Mg C ha−1 yr−1. Noting the uncertainties of the fate of macroalgal biomass carbon, we estimate the potential sequestration rate and find that it is comparable to mature terrestrial ecosystems such as tropical grasslands and temperate forests. This study demonstrates that macroalgal seasonality allows for a consistent amount of biomass carbon to either be exported and eventually sequestered, or harvested for utilization on an annual basis. These findings on macroalgal growth patterns and their considerable contributions to tropical coastal carbon pool add to the growing support for macroalgae to be formally included in blue carbon assessments.

Intrinsic Photosensitivity of the Vulnerable Seagrass Phyllospadix iwatensis: Photosystem II Oxygen-Evolving Complex Is Prone to Photoinactivation.

Phyllospadix iwatensis, a foundation species of the angiosperm-dominated marine blue carbon ecosystems, has been recognized to be a vulnerable seagrass. Its degradation has previously been reported to be associated with environmental changes and human activities, while there has been a limited number of studies on its inherent characteristics. In this study, both the physiological and molecular biological data indicated that the oxygen-evolving complex (OEC) of P. iwatensis is prone to photoinactivation, which exhibits the light-dependent trait. When exposed to laboratory light intensities similar to typical midday conditions, <10% of the OEC was photoinactivated, and the remaining active OEC was sufficient to maintain normal photosynthetic activity. Moreover, the photoinactivated OEC could fully recover within the same day. However, under harsh light conditions, e.g., light intensities that simulate cloudless sunny neap tide days and continual sunny days, the OEC suffered irreversible photoinactivation, which subsequently resulted in damage to the photosystem II reaction centers and a reduction in the rate of O2 evolution. Furthermore, in situ measurements on a cloudless sunny neap tide day revealed both poor resilience and irreversible photoinactivation of the OEC. Based on these findings, we postulated that the OEC dysfunction induced by ambient harsh light conditions could be an important inherent reason for the degradation of P. iwatensis.