Seagrasses are highly productive ecosystems and hotspots for biodiversity, providing a plethora of benefits to the environment and to people. Their value in sequestering and storing carbon is ...increasingly being recognised, as the world searches for ways to mitigate the effects and slow the pace of climate change. However, many uncertainties remain, with basic information such as average carbon stocks, variability and species-specific differences missing for many regions. This study evaluates, for the first time, the carbon storage capacity of Zostera noltii and Zostera marina from intertidal seagrass meadows in Scotland. Sediment carbon stocks in the top 50 cm from vegetated and reference unvegetated plots were quantified at 10 estuaries distributed along the Scottish east and west coasts. The organic carbon stocks in the top 50 cm of the seagrass sediment ranged from a minimum of 14.94 Mg C ha−1 at the Moray Firth to a maximum of 105.72 Mg C ha−1 at the Firth of Forth, with a mean (±SD) of 54.79 ± 35.02 Mg C ha−1 across the 10 estuaries sampled. Moreover, seagrass areas showed enhanced carbon storage compared to reference unvegetated ones, however this was highly variable across depth, and among sites and estuaries. This paper addresses key gaps in knowledge concerning the role of intertidal Scottish seagrass meadows as carbon sinks and discusses the implication of this emerging information for their effective management and conservation.
•The sediment carbon stocks of intertidal seagrass meadows were assessed in Scotland.•Sediment carbon density was highly variable across depth and among sites.•The sediment carbon stocks in the top 50 cm ranged from 14.94 to 105.72 Mg C ha−1.•Seagrass plots retained 20% more organic carbon (% DW) than unvegetated plots.
Seagrass meadows provide numerous ecosystem services and their rapid global loss may reduce human welfare as well as ecological integrity. In common with the other 'blue carbon' habitats (mangroves ...and tidal marshes) seagrasses are thought to provide coastal defence and encourage sediment stabilisation and surface elevation. A sophisticated understanding of sediment elevation dynamics in mangroves and tidal marshes has been gained by monitoring a wide range of different sites, located in varying hydrogeomorphological conditions over long periods. In contrast, similar evidence for seagrasses is sparse; the present study is a contribution towards filling this gap. Surface elevation change pins were deployed in four locations, Scotland, Kenya, Tanzania and Saudi Arabia, in both seagrass and unvegetated control plots in the low intertidal and shallow subtidal zone. The presence of seagrass had a highly significant, positive impact on surface elevation at all sites. Combined data from the current work and the literature show an average difference of 31 mm per year in elevation rates between vegetated and unvegetated areas, which emphasizes the important contribution of seagrass in facilitating sediment surface elevation and reducing erosion. This paper presents the first multi-site study for sediment surface elevation in seagrasses in different settings and species.
Seagrass meadows deliver multiple ecosystem services that are of particular importance to resource-poor coastal communities, yet they are rapidly declining globally. The Payments for Ecosystem ...Services (PES) approach has been used to fund the protection of other ‘Blue Carbon’ Ecosystems (BCE), yet seagrass has been incorporated in just one PES project worldwide. Some of the ecosystem services delivered by seagrass have the potential for inclusion under a PES framework but multiple challenges currently make this difficult, particularly under community-based management. PES programmes typically focus on carbon as the tradable service, but scientific uncertainties regarding seagrass carbon are likely to remain significant barriers to using carbon as the sole commodity under current carbon trading standards and market conditions. It is recommended here that project developers demonstrate the multiple ecosystem services delivered by seagrass meadows, along with their importance to coastal communities, in the planning and marketing of seagrass PES projects. Moreover, they should consider approaches that incorporate seagrass meadows into other blue carbon certified projects. The capacities of the communities that rely most heavily on seagrass are generally very limited. Consequently, demanding high levels of scientific certainty over carbon stocks and flows will exclude most of these communities. Standards, buyers and policy makers should consider building community capacity in the technical and marketing requirements of voluntary carbon standards. The voluntary carbon market has the flexibility to pioneer certified seagrass carbon, potentially leading to the inclusion of seagrass carbon in formal policy instruments, such as Nationally Determined Contributions (NDCs).
•Seagrass meadows deliver a plethora of ecosystem services but protection is lacking.•There has been limited inclusion of seagrass under certified carbon trading projects.•The voluntary carbon market can facilitate innovation and experimentation in CBM.•Multiple ecosystem services should be considered under certification of seagrass.•CBM of seagrass can contribute to climate, biodiversity and development targets.
The onset of a major seagrass initiative in West Africa enabled important seagrass discoveries in several countries, in one of the least documented seagrass regions in the world. Four seagrass ...species occur in western Africa, Cymodocea nodosa, Halodule wrightii, Ruppia maritima and Zostera noltei. An area of about 62,108 ha of seagrasses was documented in the studied region comprising seven countries: Mauritania, Senegal, The Gambia, Guinea Bissau, Guinea, Sierra Leone and Cabo Verde. Extensive meadows of Zostera noltei were recorded for the first time at Saloum Delta, Senegal, which represents the new southernmost distribution limit of this species. This paper also describes the seagrass morphology for some study areas and explores the main stressors to seagrasses as well as conservation initiatives to protect these newly documented meadows in West Africa. The produced information and maps serve as a starting point for researchers and managers to monitor temporal and spatial changes in the meadows’ extent, health and condition as an efficient management tool.
Population connectivity influences the distribution of genetic diversity and divergence along a species range, as the likelihood of extinction or differentiation increases in isolated populations. ...However, there is still poor understanding of the processes mediating inter-population dispersal in marine species that are sessile and lack planktonic life stages. One such case is the seagrass species
Halodule wrightii
, which produces basal seeds, although detached plants can drift. Along the tropical western coast of Africa, this species occurs in distant discontinuous habitats, raising the question of how interpopulation dispersal is mediated. The species is a key source of ecosystem functions including feeding large migratory grazers. This study aims to infer whether genetic differentiation of the seagrass
H. wrightii
along the western coast of Africa supports a hypothesis of predominant transportation of rafting seagrass by ocean currents, versus the hypothesis of biotic vectors of dispersal. Additional hypotheses were addressed concerning range-wide clonality and genetic diversity, assessed with microsatellite markers on populations of the west coast of Africa from Mauritania to Angola. Population genetic diversity and structure were compared with predictions from biophysical models of dispersal by oceanographic currents. The genetic data revealed low divergence among most populations, in strong contrast with predictions of very low probability of connectivity mediated by currents along the western African coastline. Moderate to high genotypic diversity showed important seed recruitment, but genetic and genotypic diversities were lower at range edges. Populations north and south of the equator were differentiated, and remarkably, so were neighboring equatorial populations despite their proximity. These results reveal independent sources of colonization of meadows in these islands, which are major habitat for migratory grazing green turtles, also supporting the hypothesis of biotically mediated seed transport. The importance of seagrass for conservation of endangered macrofauna has been widely reported; here we report evidence supporting the reciprocal role, that macrofauna protection can also plays a role in long-term survival and reproductive success of seagrass.
Abstract
The concentrations of six trace metals (Mn, Zn, Cu, Pb, Co and Cd) in five compartments (blades, sheaths, vertical rhizomes, main axis plus additional branches and roots) of the seagrass
...Cymodocea nodosa
from the Gulf of Thessaloniki, Greece were determined monthly, together with potential associated variables (climate variables, sediment metal concentrations, plant compartment biomass, size and age). Uni- and multivariate data analyses were applied. Univariate analyses showed that leaf blades displayed the highest annual mean concentration of most metals (Mn, Zn, Pb, Co, Cd) analyzed, whereas sheaths had the highest Cu concentration; metal concentrations in blades generally showed a wider monthly variability than those in the other plant compartments, and especially roots. The multivariate pattern of metals in leaf blades showed a seasonal periodicity that appeared to be governed by the cumulative effect of plant growth dynamics and sediment metal content. In particular, most metal concentrations increased from April onwards, with enhancement of blade biomass, size and age, and remained high throughout the blade growing season, whereas Cu concentration showed the opposite pattern; an additional increase in blade Zn concentration during early winter coincided with a marked increase in sediment Zn content. The multivariate patterns of metals in the other plant compartments showed no distinct seasonality and were not markedly related to the examined variables. These findings are not consistent with the assumption that metals in seagrass tissues display an overall seasonal trend of markedly higher levels during the cold period. The present study stresses the need for more knowledge on metal seasonality in seagrass compartments and on the associated variables.
Climate change is predicted to alter pathogen–host relationships and there is evidence of an increase in disease in both terrestrial and marine environments. Infection rates do not always increase ...linearly with temperature since thermal tolerance ranges of host and pathogens do not necessarily overlap and the host may benefit from thermal refugia of low or no disease pressure. Here, we demonstrate that climate warming may alleviate pathogen pressure in a climate-vulnerable Mediterranean seagrass, Posidonia oceanica. We tested the impact of warming on infection by Labyrinthula sp.—the causative pathogen of wasting disease—and the combined effect of elevated temperature and disease on photobiology. Infected and control shoots of P. oceanica were incubated at temperatures between 24 and 32 °C, encompassing maximum summer seawater temperatures projected for the Mediterranean Sea during the twenty-first century. Warming reduced the occurrence and severity of the disease and temperatures >28 °C inhibited cell division and growth of Labyrinthula. Photochemical efficiency was not significantly affected by short-term warming or by Labyrinthula infection. These results suggest that, unlike what has been predicted for the majority of pathogen–host relationships, warming may lead to a reduced risk of wasting disease in P. oceanica and relieve pathogen pressure from this species.
•We present long-term eelgrass flowering shoot data from the Isles of Scilly, UK.•Flowering is highly structured in time and space, increasing with sea temperature.•Survival maintains local density, ...with flowering contributing to colonisation.•Testing experimental prediction with field observation is spatial scale dependent.
Interaction between biotic and abiotic drivers of dynamics is an important topic in ecology. Despite numerous short-term studies, there is a paucity of evidence about how environmental structure modifies dynamics in marine systems. We quantified Zostera marina flowering and non-flowering shoot density annually from 1996 to 2012 around the Isles of Scilly, UK, parameterizing a population dynamic model. Flowering is structured in time and space, with temperature and flowering positively associated at some locations only. We found no evidence that flower production contributes to seagrass density but ‘patchiness’ was positively associated with flowering in the previous year. With evidence of substantial overwinter survival, findings support the hypothesis that local populations are maintained largely through vegetative reproduction but sexual reproduction may contribute to colonisation of vacant habitat. This long-term study (1) tests validity of shorter-term investigations, (2) quantifies interaction between biotic and abiotic factors and (3) promotes seagrass as a model ecosystem.
Seagrasses are marine foundation species that form ecologically important habitats in coastal areas around the world. They provide a range of ecosystem services, including coastal protection and the ...recently recognised large contribution to global carbon sequestration and storage. To date, the majority of published studies on the aforementioned ecosystem services is limited to specific geographic regions and seagrass species. This PhD study attempted to explore and provide the first evidence, to the best of our knowledge, on the role of Scottishseagrasses as carbon sinks and sediment stabilisers. In 2013, shoot dynamics of Zostera noltii plots were monitored biweekly and seasonally in the Forth estuary and digital images of the surveyed plots were taken for the development of a remote sensing technique which would accurately estimate the vegetation cover. In 2014, sediment samples from vegetated and unvegetated plots within beds of Z. marina and Z. noltii were collected from all the major estuaries along the east coast of Scotland, from the Firth of Forth in the south to Dornoch Firth in the north. Samples were analysed for organic matter, organic carbon, radionuclides 210Pb, 137Cs and 241Am, and δ13C in order to determine the organic matter and organic carbon density, longevity and sources of carbon respectively. To explore the role of seagrass in sediment deposition and stability, surface elevation was measured monthly in seagrass plots and bare sediment in the Forth estuary over two years. The results and main mechanisms underlying these findings are reported and discussed in detail in each chapter. In short, the proposed method based on digital images provided estimates of seagrass coverage that are more accurate than observers' estimates, with some constraints when macroalge and/or extreme light are present. Intertidal seagrass meadows in Scotland showed significantly enhanced carbon storage compared with bare sediment. Seagrass plots contained variable quantities of carbon in their sediments with species composition having a significant effect on carbon stocks, whereas depth and seagrass abundance had no effect on carbon stores. Despite their small above-ground biomass Scottish seagrass plots had a strong influence on sediment deposition and prevented erosion. Further research is needed to understand what factors drive large carbon sequestration and storage at some sites, thus contributing policy-relevant information on the prediction of the seagrass carbon hot-spots. Also, long-term datasets on surface elevation change are important in order to understand the effect of all the processes involved on sediment deposition in seagrass beds.
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