Coastal saltmarshes provide globally important ecosystem services including ‘blue carbon’ sequestration, flood protection, pollutant remediation, habitat provision and cultural value. Large portions ...of marshes have been lost or fragmented as a result of land reclamation, embankment construction, and pollution. Sea level rise threatens marsh survival by blocking landward migration where coastlines have been developed. Research-informed saltmarsh conservation and restoration efforts are helping to prevent further loss, yet significant knowledge gaps remain. Using a mixed methods approach, this paper identifies ten research priorities through an online questionnaire and a residential workshop attended by an international, multi-disciplinary network of 35 saltmarsh experts spanning natural, physical and social sciences across research, policy, and practitioner sectors. Priorities have been grouped under four thematic areas of research: Saltmarsh Area Extent, Change and Restoration Potential (including past, present, global variation), Spatio-social contexts of Ecosystem Service delivery (e.g. influences of environmental context, climate change, and stakeholder groups on service provisioning), Patterns and Processes in saltmarsh functioning (global drivers of saltmarsh ecosystem structure/function) and Management and Policy Needs (how management varies contextually; challenges/opportunities for management). Although not intended to be exhaustive, the challenges, opportunities, and strategies for addressing each research priority examined here, providing a blueprint of the work that needs to be done to protect saltmarshes for future generations.
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•Saltmarshes are key ecosystems for coastal biodiversity and ecosystem services.•Science-based evidence is needed for successful conservation and management.•An international, interdisciplinary network of saltmarsh experts was assembled.•10 top research priorities were identified for future saltmarsh research.
Coastal defence structures are proliferating to counter rising and stormier seas. With increasing concern about the ecological value of built environments, efforts are being made to create novel ...habitat to increase biodiversity. Rock pools are infrequent on artificial structures. We compared biodiversity patterns between rock pools and emergent rock and assessed the role of pool depth and substratum incline in determining patterns of biodiversity. Rock pools were more taxon rich than emergent substrata. Patterns varied with depth and incline with algal groups being more positively associated with shallow than deeper habitats. Substratum incline had little influence on colonising epibiota, with the exception of canopy algae in deeper habitats where vertical surfaces supported greater taxon richness than horizontal surfaces. The creation of artificial rock pools in built environments will have a positive effect on biodiversity. Building pools of varying depths and inclines and shore heights will provide a range of habitats, increase environmental heterogeneity, therefore creating more possible ecological niches, promoting local biodiversity.
•Ecological engineering aims to create ecologically friendly urban environments.•We investigated the role of pool depth and incline in shaping biodiversity patterns in rock pools.•Rock pools were more diverse than emergent substrata.•Shallow pools supported greater algal diversity than deeper pools.•Substratum incline had little influence on colonising epibiota.
Mangroves are important sinks of organic carbon (C) and there is significant interest in their use for greenhouse gas emissions mitigation. Adverse impacts on organic carbon storage potential from ...future climate change and deforestation would devalue such ambitions, thus global projections of future change remains a priority research area. We modeled the effects of climate change on future C stocks and soil sequestration rates (CSR) under two climate scenarios (“business as usual”: SSP245 and high-emissions: SSP585). Model results were contrasted with CO
2
equivalents (CO
2
e) emissions from past, present and future rates of deforestation on a country specific scale. For C stocks, we found climate change will increase global stocks by ∼7% under both climate scenarios and that this gain will exceed losses from deforestation by the end of the twenty-first century, largely due to shifts in rainfall. Major mangrove-holding countries Indonesia, Malaysia, Cuba, and Nigeria will increase national C stocks by > 10%. Under the high-end scenario, while a net global increase is still expected, elevated temperatures and wider temperature ranges are likely increase the risk of countries’ C stocks diminishing. For CSR, there will likely be a global reduction under both climate change scenarios: 12 of the top 20 mangrove-rich countries will see a drop in CSR. Modeling of published country level mangrove deforestation rates showed emissions have decreased from 141.4 to 6.4% of annual CSR since the 1980’s. Projecting current mangrove deforestation rates into the future resulted in a total of 678.50 ± 151.32 Tg CO
2
e emitted from 2012 to 2095. Reducing mangrove deforestation rates further would elevate the carbon benefit from climate change by 55–61%, to make the proposition of offsetting emissions through mangrove protection and restoration more attractive. These results demonstrate the positive benefits of mangrove conservation on national carbon budgets, and we identify the nations where incorporating mangrove conservation into their Nationally Defined Contributions offers a particularly rewarding route toward meeting their Glasgow Agreement commitments.
Coastal salt marshes are threatened by erosion from storminess and sea level rise, with resulting losses in flood protection, wildlife and recreational space. Although more than $1 billion has been ...spent to reconcile losses, restoration has had varying success because of poor survival of planted patches in challenging wave and current conditions. Marsh expansion after colonization or replanting is regulated by positive and negative feedbacks between vegetation density and sediment capture. Dense vegetation stimulates sediment capture and vertical patch growth, but negatively constrains patch expansion by concentrating hydrological energy into erosion gullies along patch edges. Conversely, low‐density vegetation may not simulate enough sediment capture, which increases plant dislodgement mortality. The strengths of positive and negative feedbacks will vary with wave exposure, but this has never been tested in natural conditions.
We observed density‐dependent sediment feedbacks, survival and lateral expansion by Sporobolus anglicus patches (0.8 × 0.8 m) planted at three levels of vegetation density, at each of three levels of wave forcing (three sites).
We found interactive effects of plant density and forcing on the strength of positive and negative feedbacks. Density‐dependent feedbacks only emerged in moderate and exposed conditions: classic marsh tussock patch shapes, which arise due to combined positive (vertical growth) and negative (gullies) feedbacks, were only associated with high density vegetation under exposed conditions. At high exposure, survival was enhanced by dense planting, which diverted energy away from the vegetation. In sheltered conditions, expansion was the greatest at medium density, while dense patches had high mortality and erosion.
Synthesis and applications. Success of wetland restoration clearly hinges on considering interactions between environmental stress and planting density. In challenging high‐exposure settings, dense planting in large patches should maximize success, as plant facilitation boosts sediment capture and negative edge effects (gullies) will represent a diminished proportion of larger patches. Yet, benefits of dense planting will switch from positive (facilitation) to negative (competition) with reduced environmental stress, when moderate‐density planting might be optimal. Switches along stress gradients between positive and negative feedbacks are common across ecosystems. We call for wider integration of facilitation and stress–gradient principles into restoration design to safeguard restoration successes.
Success of wetland restoration clearly hinges on considering interactions between environmental stress and planting density. In challenging high‐exposure settings, dense planting in large patches should maximize success, as plant facilitation boosts sediment capture and negative edge effects (gullies) will represent a diminished proportion of larger patches. Yet, benefits of dense planting will switch from positive (facilitation) to negative (competition) with reduced environmental stress, when moderate‐density planting might be optimal. Switches along stress gradients between positive and negative feedbacks are common across ecosystems. We call for wider integration of facilitation and stress–gradient principles into restoration design to safeguard restoration successes.
Complex networks of above-ground roots and trunks make mangrove forests trap plastic litter. We tested how macroplastics relate to tree biomass, root abundance, mangrove geomorphology and river mouth ...proximity, surveying landward and seaward margins of seven forests in the Philippines, a global hotspot for marine plastic pollution. Macroplastics were abundant (mean ± s.e.: 1.1 ± 0.22 items m−2; range: 0.05 ± 0.05 to 3.79 ± 1.91), greatest at the landward zone (mean ± s.e.: 1.60 ± 0.41 m−2) and dominated by land-derived items (sachets, bags). Plastic abundance and weight increased with proximity to river mouths, with root abundance predicting plastic litter surface area (i.e., the cumulative sum of all the surface areas of each plastic element per plot). The study confirms rivers are a major pathway for marine plastic pollution, with mangrove roots are the biological attribute that regulate litter retention. The results suggest land-based waste management that prevent plastics entering rivers will reduce marine plastic pollution in Southeast Asia.
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•Mangrove plastic debris rise with proximity to river mouth.•Landward zones have higher quantities of plastics than seaward zones.•Plastic capture is explained by above-ground root abundance.•Tree biomass does not boost plastic capture.•Plastic pollution is linked to mangrove geomorphological type.
Global inventories that show mangrove forests have rich carbon stores currently lack data from arid areas where carbon stocks may be functionally impoverished relative to humid regions. We quantified ...total carbon stocks (C) of three arid Avicennia marina stands in Qatar and report an aboveground biomass allometric equation and the first below ground biomass allometric equation in the region. The allometric relationships indicate that below ground mangrove C stocks in arid locations are more important than previously reported. Comparison of previously published and our locally developed allometric equations show that A. marina in Qatar allocate comparatively more biomass to below ground components than the same species in tropical humid settings, which is consistent with plant adaptations to living in stressed conditions. Total C stocks were 45.70 ± 3.70 Mg C ha−1, of which tree and soil C stocks to 50 cm depth represented 10.18 ± 0.82 Mg C ha−1 and 35.52 ± 2.88 Mg ha−1 respectively. Soil C stocks to 1 m depth were 50.17 ± 6.27 Mg C ha−1. Overall, mangroves sustain relatively small C stocks in the arid, hypersaline environment of Qatar, which may be due to both relatively low tree productivity and growth, as well as limited rainfall-driven transport of terrigenous sediment inputs. By providing further estimates of mangrove carbon at their climatic extremes, these results can contribute to a better quantification of global mangrove carbon, reduce uncertainty in below ground tree C estimates from arid mangroves and have implications for mangrove carbon stocks in the face of climate change.
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•The study quantified total carbon stocks of arid Avicennia marina stands in Qatar.•We report the first below ground biomass allometric equation for A. marina in the region.•A. marina in Qatar had higher below carbon partitioning than the same species from the tropics.•Carbon stocks were lower than other tropical regions.
The plant economic spectrum (PES) predicts a suite of correlated traits in a continuum from resource conservation to rapid resource acquisition. In addition to competing for resources, plants need to ...cope with other environmental stresses to persist and reproduce. Yet, it is unclear how multiple strategies (i.e. traits uncorrelated with the PES) affect plant biomass allocation, hindering our ability to connect environmental gradients to ecosystem services.
We examined intraspecific dimensionality of leaf and root traits in the salt marsh pioneer species Spartina anglica across salinity, redox and sand content gradients, and related them to above‐ground and below‐ground plant biomass—properties associated with wave attenuation and sediment stabilization in coastal marshes.
Through principal component analysis, we did not find support for a single PES trait dimension (strategy), but instead identified four trait dimensions: (a) leaf economic spectrum (LES, leaf analogue of PES); (b) fine roots‐rhizomes; (c) coarse roots; and (d) salt extrusion. Structural equation modelling showed a shift towards the conservative side of the LES under increasing salinity, while redox had a positive influence on the coarse roots dimension. In turn, these trait dimensions were strongly associated with above‐ground and below‐ground biomass (BLW biomass) allocation.
These results indicate that under high salinity, plants will adopt a conservative strategy and will invest more in BLW biomass. Yet, high sediment redox would still allow plants to invest in above‐ground biomass. Therefore, plants' trait‐mediated biomass allocation depends on the specific combination of abiotic factors experienced at the local scale.
Synthesis. Our study highlights the importance of considering multiple ecological strategies for understanding the effect of the environment on plants. Abiotic stresses can influence multiple trait strategy‐dimensions, with consequences for ecosystem functioning.
Sommario
Lo spettro economico delle piante (SEP) postula che i tratti funzionali delle piante si distribuiscano lungo un continuum dalla conservazione all'acquisizione delle risorse. Oltre a competere per le risorse, le piante devono anche resistere allo stress ambientale se vogliono sopravvivere e riprodursi. Ciónonostante, non é ancora chiaro come strategie multiple (i.e. tratti correlati con il SEP) influiscano sull'allocazione della biomassa nelle piante, riducendo la nostra capacitá di legare gli effetti dei gradienti ambientali sui servizi dell'ecosistema.
Abbiamo esaminato la dimensionalitá nei tratti funzionali di radici e foglie a livello intraspecifico della pianta pioniera laguanare Spartina anglica lungo gradienti di salinitá, redox e sabbia, e l'abbiamo legata alla biomassa apo‐ ed ipogea che é associata alla capacitá di attenuazione delle onde e della stabilizzazione del sedimento nelle lagune costiere.
Attraverso l'analisi dei componenti principali, non abbiamo trovato supporto per una singola strategia SEP, ma abbiamo identificato quattro strategie: (a) lo spettro economico delle foglie (SEL, analogo fogliare del SEP); (b) radici fini – rizomi; (c) radici grossolane; e (d) estrusione fogliare di sale. Modelli di equazioni strutturali hanno dimostrato uno spostamento verso il lato conservativo del SEL all'aumentare dello stress salino, mentre una riduzione dello stress redox ha positivamente influenzato la produzione di radici grossolane. Di conseguenza, a queste dimensioni nei tratti funzionali era fortemente associata all'allocazione apo‐ ed ipogea delle biomassa delle piante.
Questi risultati indicano che all'aumentare della salinitá le piante adottano una strategia di conservazione delle risorse ed investono maggiormente nella porsione ipogea. Ciónonostante, se le medesime piante crescono in sedimenti con alto redox, allora esse sono in grado di investire biomassa anche nella porzione apogea. Quindi, l'allocazioni di biomassa mediata dai tratti funzionali dipende dalla specifica combinazione dei fattori ambientali che a cui la pianta é sottoposta a livello locale.
Sintesi. Il nostro studi sottolinea l'importanza di considerare diverse strategie ecologiche per capire quali effetti l'ambiente ha sulle piante. Gli stress aboitici possono influenzare questa multi‐dimensionalitá dei tratti funzionali, con consequenze per il funzionamento degli ecosistemi.
Our focal saltmarsh grass expressed conservative leaf traits and invested more in below‐ground biomass under high salinity. Yet, it was still able to express a high proportion of coarse roots and produce greater above‐ground biomass under high redox. Therefore, our study highlights the importance of multiple trait dimensions in connecting the environment to plant biomass allocation and ultimately ecosystem functions.
Over the last decades, population densities in coastal areas have strongly increased. At the same time, many intertidal coastal ecosystems that provide valuable services in terms of coastal ...protection have greatly degraded. As a result, coastal defense has become increasingly dependent on man-made engineering solutions. Ongoing climate change processes such as sea-level rise and increased storminess, require a rethinking of current coastal defense practices including the development of innovative and cost-effective ways to protect coastlines. Integrating intertidal coastal ecosystems within coastal defense schemes offers a promising way forward. In this perspective, we specifically aim to (1) provide insight in the conditions under which ecosystems may be valuable for coastal protection, (2) discuss which might be the most promising intertidal ecosystems for this task and (3) identify knowledge gaps that currently hamper application and hence need attention from the scientific community. Ecosystems can contribute most to coastal protection by wave attenuation in areas with relatively small tidal amplitudes, and/or where intertidal areas are wide. The main knowledge gap hampering application of intertidal ecosystems within coastal defense schemes is lack in ability to account quantitatively for long-term ecosystem dynamics. Such knowledge is essential, as this will determine both the predictability and reliability of their coastal defense function. Solutions integrating intertidal ecosystems in coastal defense schemes offer promising opportunities in some situations, but require better mechanistic understanding of ecosystem dynamics in space and time to enable successful large-scale application.
•We identify research needs for using intertidal ecosystems for coastal protection.•Ecosystems provide most protection when tides are small and areas are wide.•There is need for data on true protection value under extreme storm conditions.•We lack knowledge on long-term ecosystem persistence.•We lack insights in thresholds for ecosystem establishment and degradation.
Saltmarshes are a crucial component of the coastal carbon (C) system and provide a natural climate regulation service through the accumulation and long-term storage of organic carbon (OC) in their ...soils. These coastal ecosystems are under growing pressure from a changing climate and increasing anthropogenic disturbance. To manage and protect these ecosystems for C and to allow their inclusion in emissions and natural-capital accounting, as well as carbon markets, accurate and reliable estimates of OC accumulation are required. However, globally, such data are rare or of varying quality. Here, we quantify sedimentation rates and OC densities for 21 saltmarshes in Great Britain (GB). We estimate that, on average, saltmarshes accumulate OC at a rate of 110.88 ± 43.12 g C m−2 yr−1. This is considerably less than widely applied global saltmarsh averages. It is therefore highly likely that the contribution of northern European saltmarshes to global saltmarsh OC accumulation has been significantly overestimated. Taking account of the climatic, geomorphological, oceanographic, and ecological characteristics of all GB saltmarshes and the areal extent of different saltmarsh zones, we estimate that the 451.65 km2 of GB saltmarsh accumulates 46,563 ± 4353 t of OC annually. These low OC accumulation rates underline the importance of the 5.20 ± 0.65 million tonnes of OC already stored in these vulnerable coastal ecosystems. Going forward the protection and preservation of the existing stores of OC in GB saltmarshes must be a priority for the UK as this will provide climate benefits through avoided emissions several times more significant than the annual accumulation of OC in these ecosystems.
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•We conducted the first national saltmarsh OC accumulation assessment for Great Britian.•On average Great Britain saltmarshes accumulate 110.88 ± 43.12 g C m−2 yr−1.•Annually, 46,563 ± 4353 t of OC accumulate in Great Britian's saltmarshes.•The rate at which these saltmarshes accumulate OC is lower than previous estimates.•The low accumulation rates highlight the need to protect the OC locked in the soil.
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