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Seagrasses are important marine plants that provide a variety of ecosystem services, including food and shelter for marine life, and protection from coastal erosion. This study investigated the biodiversity (alpha and beta diversity) of seagrass in the Kepulauan Banyak Marine Nature Park, Indonesia, with a specific focus on eight sites. Alpha diversity was calculated using Shannon's index, Simpson's index, and Pielou evenness. Beta diversity was determined using Bray-Curtis dissimilarity and Jaccard dissimilarity allowing us to examine the variations in species composition among different sites. Principal coordinate analysis and Partial distance-based redundancy analysis was used to visualize and investigate the impact of constraint variables to the structure of the seagrass communities. Alpha diversity varied among the sites, with the highest alpha diversity found at the Orongan and Matahari site and the lowest at the Ujung Lolok and Balai sites. The dominant substrate type (mud or sand) was found to be a significant (P≤ 0.01) determinant of seagrass alpha diversity, with mud substrates supporting higher diversity than sand substrates. The relationship between alpha diversity and constrain variables was only significant with closest distance to forest lost and longitude variables. The analysis found that water pH, closest distance to forest lost, mean distance to tourism spots, and closest distance to settlement collectively explained a significant (P≤ 0.001) portion (88.48%) of the variation in beta diversity of seagrass across the sites. The results of this study can be used to develop management strategies for the conservation of seagrass meadows in the park. [ABSTRACT FROM AUTHOR]

A review of available research into the blue carbon potential of seagrass was undertaken. This was then used to inform an analysis of the potential current, historic, and future value of carbon sequestered and stored in the Essex Estuaries Special Area of Conservation (SAC). The assessed status of Zostera in the SAC highlights the extent of historic loss and continued degradation of this designated sub-feature, and current water quality is incompatible with recovery or restoration. Seagrass blue carbon currently stored within the SAC equates to ∼18,350 t C at a sequestration rate of 117.15 t C yr−1, with a lost/potential of 534,700 t C storage capacity. The calculated financial value of current stocks (£4.6 m) is dwarfed by the lost/potential monetary value of carbon storage, £135 m, and the forfeited sequestration of £860,000-worth of carbon annually from degraded habitat. The use of carbon offset credits could help fund the huge potential for restoration that exists within the SAC. [ABSTRACT FROM AUTHOR]

Seagrass ecosystems sequester carbon at disproportionately high rates compared to terrestrial ecosystems and represent a powerful potential contributor to climate change mitigation and adaptation projects. However, at a local scale, rich heterogeneity in seagrass ecosystems may lead to variability in carbon sequestration. Differences in carbon sequestration rates, both within and between seagrass meadows, are related to a wide range of interrelated biophysical and environmental variables that are difficult to measure holistically using traditional field surveys. Improved methods for producing robust, spatially explicit estimates of seagrass carbon storage across large areas would be highly valuable, but must capture complex biophysical heterogeneity and variability to be accurate and useful. Here, we review the current and emerging literature on biophysical processes which shape carbon storage in seagrass beds, alongside studies that map seagrass characteristics using satellite remote sensing data, to create a blueprint for the development of remote sensing-enabled proxies for seagrass carbon stock and sequestration. Applications of satellite remote sensing included measuring seagrass meadow extent, estimating above-ground biomass, mapping species composition, quantifying patchiness and patch connectivity, determining broader landscape environmental contexts, and characterising seagrass life cycles. All of these characteristics may contribute to variability in seagrass carbon storage. As such, remote sensing methods are uniquely placed to enable proxy-based estimates of seagrass carbon stock by capturing their biophysical characteristics, in addition to the spatiotemporal heterogeneity and variability of these characteristics. Though the outlined approach is complex, it is suitable for accurately and efficiently producing a full picture of seagrass carbon stock. This review has drawn links between the processes of seagrass carbon sequestration and the capabilities of remote sensing to detect and characterise these processes. These links will facilitate the development of remote sensing-enabled proxies and support spatially explicit estimates of carbon stock, ensuring climate change mitigation and adaptation projects involving seagrass are accounted for with increased accuracy and reliability. [ABSTRACT FROM AUTHOR]

Coastal vegetated ecosystems such as saltmarshes and seagrasses are important sinks of organic carbon (OC) and total nitrogen (TN), with large global and local variability, driven by the confluence of many physical and ecological factors. Here we show that sedimentary OC and TN stocks of intertidal saltmarsh (Sporobolus maritimus) and seagrass (Zostera noltei) habitats increased between two- and fourfold along a decreasing flow velocity gradient in Ria Formosa lagoon (south Portugal). A similar twofold increase was also observed for OC and TN burial rates of S. maritimus and of almost one order of magnitude for Z. noltei. Stable isotope mixing models identify allochthonous particulate organic matter as the main source to the sedimentary pools in both habitats (39–68%). This is the second estimate of OC stocks and the first of OC burial rates in Z. noltei, a small, fast-growing species that is widely distributed in Europe (41,000 ha) and which area is presently expanding (8600 ha in 2000s). Its wide range of OC stocks (29–99 Mg ha−1) and burial rates (15–122 g m2 y−1) observed in Ria Formosa highlight the importance of investigating the drivers of such variability to develop global blue carbon models. The TN stocks (7–11 Mg ha−1) and burial rates (2–4 g m−2 y−1) of Z. noltei were generally higher than seagrasses elsewhere. The OC and TN stocks (29–101 and 3–11 Mg ha−1, respectively) and burial rates (19–39 and 3–5 g m−2 y−1) in S. maritimus saltmarshes are generally lower than those located in estuaries subjected to larger accumulation of terrestrial organic matter. [ABSTRACT FROM AUTHOR]

Increasing the protection of coastal vegetated ecosystems has been suggested as one strategy to compensate for increasing carbon dioxide (CO2) in the atmosphere as the capacity of these habitats to sequester and store carbon exceeds that of terrestrial habitats. Seagrasses are a group of foundation species that grow in shallow coastal and estuarine systems and have an exceptional ability to sequester and store large quantities of carbon in biomass and, particularly, in sediments. However, carbon stocks (Corg stocks) and carbon accumulation rates (Corg accumulation) in seagrass meadows are highly variable both spatially and temporally, making it difficult to extrapolate this strategy to areas where information is lacking. In this study, Corg stocks and Corg accumulation were determined at 11 eelgrass meadows across New England, representing a range of eutrophication and exposure conditions. In addition, the environmental factors and structural characteristics of meadows related to variation in Corg stocks were identified. The objectives were accomplished by assessing stable isotopes of δ13C and δ15N as well as %C and %N in plant tissues and sediments, measuring grain size and 210Pb of sediment cores, and through assessing site exposure. Variability in Corg stocks in seagrass meadows is well predicted using commonly measured environmental variables such as grain size distribution. This study allows incorporation of data and insights for the northwest Atlantic, where few studies on carbon sequestration by seagrasses have been conducted. [ABSTRACT FROM AUTHOR]

The paper presents a study on the relative importance of wind regime and wave fetch for limitation of seagrass spatial distribution in Burgas Bay, the Black Sea. In Burgas Bay the relative importance of both factors is obviously changing from northern to southern coasts. The seagrass meadows facing north-northeast direction have two times smaller integral fetch and are three times more often wave impacted than those facing south-southeast. Along the southern coast the fetch (maximum and number of azimuths) is more important to allow seagrass presence, while in front of the northern coast - it is the wind speed recurrence. In the first scenario the habitat is expected to be less frequently but more strongly affected by the wave action, contrary to the second scenario, where the reversed effect is supposed. [ABSTRACT FROM AUTHOR]

Seagrass meadows are productive ecosystems that contribute to climate change mitigation by accumulating 'Blue Carbon' in their plant biomass and sediments. However, there is wide variation in reported sediment carbon stocks (Cstocks) across different global regions and between meadows composed of different seagrass species. Therefore, understanding the drivers for sediment Cstocks variation is crucial to developing effective conservation and restoration projects for seagrass ecosystems. This study analyses the influence of environmental factors on the variation in sediment Cstocks for six intertidal seagrass meadows within the Solent region, in southern England. There were significant differences between sites for all variables, except leaf density, and concentrations of the sediment pore water nutrients. Sediment dry bulk density, mean grain size, sorting coefficient, % mud, elevation above sea level, and pore water salinity showed high levels of association with Cstocks when assessed individually. Multivariate analyses showed that sediment dry bulk density, sorting coefficient, % mud, and pore water pH and concentration of nutrients greatly influenced Cstock. Moreover, sediment characteristics acted in conjunction to explain most of the variation in Cstock among sites. Therefore, sediment characteristics should be considered as important indicators for carbon storage potential in intertidal temperate seagrass meadows. [ABSTRACT FROM AUTHOR]

There is increasing urgency to implement climate change mitigation strategies that enhance greenhouse gas removal from the atmosphere and reduce carbon dioxide (CO2) emissions. Recently, coastal "blue carbon" habitats⁠—mangroves, salt marshes, and seagrass meadows—have received attention for their ability to capture CO2 and store organic carbon (OC), primarily in their sediments. Across habitat types and regions, however, information about the sequestration rates and sources of carbon to local sediments remains sparse. Here we compiled recently obtained estimates of sediment OC stocks and sequestration rates from 139 cores collected from temperate seagrass (Zostera marina) meadows in Alaska, British Columbia, Washington, and Oregon. Across all cores sediment OC content averaged 0.75%. Organic carbon stocks in the top 25 cm and 1 m of the sediment averaged 1,846 and 7,168 g OC m−2, respectively. Carbon sequestration rates ranged from 4.6 to 93.0 g OC m−2 yr−1 and averaged 24.8 g OC m−2 yr−1. Isotopic data from this region suggest that OC in the sediments is largely from noneelgrass sources. In general, these values are comparable to those from other temperate Z. marina meadows, but significantly lower than previously reported values for seagrasses globally. These results further highlight the need for local and species‐level quantification of blue carbon parameters. While temperate eelgrass meadows may not sequester and store as much carbon as seagrass meadows elsewhere, climate policy incentives should still be implemented to protect existing sediment carbon stocks and the other critical ecosystem services associated with eelgrass habitats. Plain Language Summary: As we search for innovative solutions to capture and store atmospheric carbon, coastal wetlands are doing so for free and at rates greater than mature forests. The carbon market, by brokering carbon offset monies, can fund coastal wetland restoration projects where a net greenhouse gas reduction can be shown. Yet seagrass carbon sequestration capacity varies among species and even within meadows of the same species. Thus, obtaining site‐specific carbon storage values is essential for restoration planning. Here we report carbon stocks and sequestration rates compiled from 30 eelgrass meadows (Zostera marina) in Oregon, Washington, British Columbia, and Alaska, areas underrepresented in current literature. We then compare these findings to previously reported values for Z. marina and for seagrasses globally. While carbon stocks and sequestration rates varied at small spatial scales, we observed no latitudinal patterns. Our values were similar to those found in other Z. marina meadows, but significantly lower than global seagrass averages. Through isotopic analysis we found that the majority of the carbon originated from noneelgrass sources and very little from eelgrass itself. These results, the first to reveal eelgrass carbon sequestration capacities in the Northeastern Pacific, expose the importance of obtaining local values for carbon sequestration. Key Points: Sediment carbon content varied both within and among Northeast Pacific eelgrass meadows, yet there was no clear latitudinal trendCarbon in eelgrass meadow sediments appears to be derived largely from noneelgrass sourcesNortheast Pacific carbon stocks and accumulation rates are comparable to other Z. marina meadows but lower than global seagrass values [ABSTRACT FROM AUTHOR]

Ten percent of all organic carbon (Corg) absorbed by the ocean each year is stored in seagrass‐bearing sediments. The preservation of these carbon stores is considered a vital method to mitigate climate change. Seagrass‐bearing sediments have been correlated with sediment geophysical properties yet have not been related to sediment acoustic properties. For this purpose, sediment cores were collected from a Thalassia testudinum seagrass meadow in South Texas, USA, where geophysical, acoustical, and Corg properties were measured. It is hypothesized that when deposits of Corg adsorb onto mineral surfaces and are stored in pore spaces, compliant layers between grain contacts and the formation of an organic‐rich suspension reduce sediment stiffness. Results from this seagrass meadow demonstrated a strong correlation between sediment P wave modulus and Corg and show promise toward the development of an in situ ultrasonic sediment probe to more rapidly quantify and monitor seagrass carbon stores. Key Points: Seagrass‐bearing sediment P wave modulus correlated better with organic carbon content than with mud contentPresence of organic carbon between grains can affect bulk wave propagationEx situ results show promise for rapid in situ organic carbon estimation within the studied seagrass meadow [ABSTRACT FROM AUTHOR]

An extensive area of seagrass covering the shore of part of the South African estuary ranked highest in overall national conservation and biodiversity importance (the Knysna estuarine bay) was killed by a series of seasonal green‐tidal blankets of Ulva starting in the late austral summer of 2015, leaving bare muddy sediment. An earlier (2011) survey of then seagrass macrobenthic assemblages at 27 stations along over 1 km of that shore was exactly repeated in 2018 after this event.After loss of seagrass, intertidal macrofauna became significantly less speciose (1:0.61), spatially and systematically more uniform (1:1.30 and 1:1.63), but more (not the usual less) abundant (0.62:1). Assemblage composition also changed, with polychaete numbers (small nereidids, spionids, fabriciids and an endemic paraonid) increasing from <50% of total macrofaunal individuals to >90% (although cirratulids decreased), whereas small malacostracan crustaceans (except the amphipod Grandidierella sp.) and microgastropods diminished to insignificant levels—microgastropods for reasons possibly unconnected with the green tide.Comparison with areas not vegetated in 2014, however, indicated that although macrofaunal abundance was greater in the 2018 Ulva‐induced bare areas, levels of per unit area biodiversity (number of species, species and taxonomic diversity per station) were comparable. This suggests that the effect of local loss of seagrass cover is context dependent, particularly with regard to pre‐existing local seagrass versus adjacent bare‐sediment differentials, and does not necessarily lead to any "degraded" state.Decreased local importance of small malacostracans may severely impact the region's usage by the adult and juvenile fish for which it is an important nursery and feeding ground. [ABSTRACT FROM AUTHOR]

Despite the importance of coastal ecosystems for the global carbon budgets, knowledge of their carbon storage capacity and the factors driving variability in storage capacity is still limited. Here we provide an estimate on the magnitude and variability of carbon stocks within a widely distributed marine foundation species throughout its distribution area in temperate Northern Hemisphere. We sampled 54 eelgrass (Zostera marina) meadows, spread across eight ocean margins and 36° of latitude, to determine abiotic and biotic factors influencing organic carbon (Corg) stocks in Zostera marina sediments. The Corg stocks (integrated over 25‐cm depth) showed a large variability and ranged from 318 to 26,523 g C/m2 with an average of 2,721 g C/m2. The projected Corg stocks obtained by extrapolating over the top 1 m of sediment ranged between 23.1 and 351.7 Mg C/ha, which is in line with estimates for other seagrasses and other blue carbon ecosystems. Most of the variation in Corg stocks was explained by five environmental variables (sediment mud content, dry density and degree of sorting, and salinity and water depth), while plant attributes such as biomass and shoot density were less important to Corg stocks. Carbon isotopic signatures indicated that at most sites <50% of the sediment carbon is derived from seagrass, which is lower than reported previously for seagrass meadows. The high spatial carbon storage variability urges caution in extrapolating carbon storage capacity between geographical areas as well as within and between seagrass species. Key Points: The Z. marina Corg stocks varied widely within and across studied regions; majority of this variation was explained by five sediment and environmental variablesThe Z. marina Corg stocks were comparable to other seagrass species and other blue carbon habitats such as salt marshes and mangrove forestsCarbon isotopic signatures indicated that at most sites, only less than half of the sediment carbon is derived from seagrass, though variation was significant [ABSTRACT FROM AUTHOR]