Salt marshes to fight climate change

Salt marshes to fight climate change

Climate change is upon us, and the urgency to act against it has never been so high. The ever-increasing emission of carbon dioxide over the past century must be reversed and has become a global priority. The sea level is rising, and the frequency and intensity of extreme weather events are increasing, putting our shorelines and coastal communities at increased risk of flooding. Marine coastal ecosystems are vital for human health and well-being for all the services they provide to people, from food provision to coastal protection and more. Salt marshes are coastal wetlands flooded and drained by salt water brought in by the tides that occur worldwide, particularly in middle to high latitudes. As a marine and coastal ecosystem, they are excellent habitats for climate change adaptation and mitigation, and here is why.

Salt marshes in the National Park of Banc d’Arguin, Mauritania. Credit: Ewan Trégarot

A colossal carbon sink to mitigate Greenhouse Gases emissions

The main cause of climate change is the emission of greenhouse gases such as carbon dioxide, nitrous oxide, methane. Salt marshes are highly effective to store carbon, as they absorb the carbon dioxide from the atmosphere and lock it into the ground through the capture of organic sediment rich in organic matter (in a nutshell!). Globally, for terrestrial forest systems, the average carbon burial rate range between 4 to 5 g/m2/year. For salt marshes, the rates have been measured at an average of 218 g/m2/year, which is about 50 times more than terrestrial forests! The blue carbon potential of vegetated marine ecosystems is enormous, and its valuation (in monetary terms) has the potential to create opportunities to fund the restoration, conservation, and protection of saltmarshes to contribute to climate change mitigation. This is achieved by generating carbon credits through restoration activities that follow an official methodology approved by carbon offset mechanisms, such as the Verified Carbon Standards.

 However, human activities can alter the capacity of salt marshes to sequester blue carbon, and loss of blue carbon from salt marshes has been reported due to land reclamation, chemical and physical disturbances, and eutrophication. Sea-level rise and climate change may also influence carbon sequestration within tidal marshes either positively or negatively. More research is still needed to understand those highly complex processes.

A great coastal defence against sea-level rise

Sea-level rise is a significant threat to our coastline around the world. Even if a low carbon emissions trajectory is followed, the global mean sea level is projected to rise between 0.29 and 0.59 m by 2100 relative to 1986–2005, according to the last IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. Being at the interface between land and sea, salt marshes, like other vegetated marine and coastal ecosystems, are important flood and coastal defence, and critical in reducing disaster risk in low-lying coastal zones. As a matter of fact, they support three essential functions for coastal protection: wave attenuation, storm surge reduction, and seabed elevation. Indeed, the amount of waves energy reaching the shore depends on the bathymetry or state of ocean floors, the slope, and the sediment properties of the seabed. In the presence of salt marshes, the plants’ stiffness, density, leaf length, and morphology further dissipate wave energy, increase bottom friction, and reduce current flows and turbulences. Belowground, the root systems secure sand fixation, allow high sediment accretion rates and shore stability. Through sediment accretion rate or change in elevation, the marshes can respond to the elevation in sea level as the way they build up vertically is key to keeping up with sea-level rise. To ensure this function, salt marshes also require healthy associated ecosystems, like mudflats or intertidal seagrass beds, to maintain high elevation and limit the attacks of waves on salt marshes fringe.

Protecting the remaining salt marshes is a matter of urgency, but there is also potential to restore and create new habitats. By removing coastal defences or moving them further inland, ‘Managed realignment’ is one way of creating new habitat, and is one of the UK adaptation measures to increase carbon storage, and reduce risks of flooding and coastal erosion. In fact, plans are to realign 10% of England’s coastal zone by 2030 which would create 6,200 ha of new habitat. A great example of coastal realignment is the Medmerry project, which is one of the few marine Nature-based Solutions to date according to the IUCN global standards.

Illustration of the managed realignment at Medmerry 2011. Credit: Google Earth
Illustration of the managed realignment at Medmerry 2019. Credit: Google Earth

One of the most noticeable effects of climate change is the increasing frequency and severity of storms. If the climate continues to warm and sea levels continue to rise, the effects of these storms could be devastating, putting these and other coastal communities worldwide at risk.

And much more that we know and we don’t know…

Beyond being a carbon sink and a great coastal defence against flood, these intertidal habitats are essential for healthy fisheries and communities, and they are an integral part of our economy and culture. They also provide essential food, refuge, or nursery habitat for many species of fish and shrimps of commercial interest.They mitigate flooding by slowing and absorbing rainwater and protecting water quality by filtering runoff and metabolizing excess nutrients. However, salt marshes globally have seen their ecological condition and physical properties degraded by the combined effects of climate change and anthropogenic stressors such as pollution and land-use practices. The resulting decline in the coastal protection service they provide put coastal infrastructures and populations even more at risk in the face of climate change. The cumulative impact of climate change and anthropogenic activities on the state of saltmarshes and their ability to provide ecosystem services remains largely unknown. It is one of the main challenges the MaCoBioS project will attempt to solve. Our experts will soon collect in-situ data in the salt marshes of the Southern UK and Ireland across a gradient of environmental conditions and protection measures. Stay tuned for fieldwork updates and results!

You could get involved in protecting these fabulous habitats

Want to contribute to the research on salt marshes? If you are based in the UK, The Saltmarsh App gives you all you need to know to collect essential plant and soil data. Next time you take a walk by the sea or take out your binoculars to enjoy the richness and abundance of birds on saltmarshes, why not collect a few data? Or else you can help spread the word on this amazing natural habitat, highlighting its importance for human well-being and fighting climate change.

Text by Ewan Trégarot, with the help of Mialy Andriamahefazafy and Cindy Cornet

For further reading:

IPCC Special Report on the Ocean and Cryosphere in a Changing Climate:

Managed realignment:

Salt marshes research and App:

Verified Carbon Standards:

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Corals: environmental records of the past

Corals: environmental records of the past

Humans are wonderful creatures; our intellect has allowed us to thrive on this planet through impressive technological and scientific advances. However, this success has come at a cost. For example, most marine ecosystems are now under pressure from a variety of stressors mostly linked to human activities. In the case of coral reefs, these stressors include a combination of global pressures in the form of warming and ocean acidification, and local pressures which include overfishing, habitat destruction, pollution, increased sedimentation, to name just a few. This pressure has caused a worldwide loss and degradation of coral reefs; however, there are still questions about the full scale of these changes and on the ability of corals to withstand them. For example, we know that extreme heat can kill corals, but it is not fully understood how quickly corals can increase their tolerance to thermal stress, or how local and global stressors interact with each other. The latter is crucial because while fixing global warming and ocean acidification requires a global effort, but local governments and managers can implement policies to remove or reduce local stressors and give corals a better fighting chance in the face of climate change.

Massive colony of Sidereastrea siderea colony in Martinique. Photo: Jean-Philippe Maréchal (2021).

One of the reasons for current knowledge gaps is the lack of long-term temporal observations of key environmental parameters, such as temperature, salinity, or the pH of seawater. Historically, we either lacked the technology to monitor these parameters, access to such technology was expensive or there was no clear understanding of the need to monitor these parameters. Therefore, to put current changes in perspective, accounting for natural variability, it is necessary to find ways to fill knowledge gaps, and corals can help us to do so!

Reef forming corals precipitate a calcium carbonate skeleton that forms the reef foundation.  These skeletons come in all shapes and sizes, from the delicate and intricate branching corals to the massive types that are named as such due to their stable ball- or boulder-shaped skeleton. The skeletons of corals are attractive to paleoceanographers because they can tell us about the past, if you know how to read the stories recorded in their skeletons. This is because corals continuously deposit new layers on top of their older skeleton, thus growing bigger and bigger every year and creating a record of their history. Some massive corals can become real life giants as the can live for several centuries, never ceasing to grow. The oldest massive corals are believed to be nearly a thousand years old. But corals are living organisms that respond to their environment as we do, and their skeleton records these changes in a similar way to trees forming rings. In winter, when the waters are cold, corals tend to grow slower and form a denser skeleton while in summer, when it is warmer, corals usually grow faster and form a less dense skeleton. Therefore the skeleton of a massive coral records this seasonal rhythm in the form of annual bands that resemble the rings in the trunk of a tree.

X-ray image from a core of a massive coral showing the annual density bands.

If a year is unsually cold or warm this influences the average growth rate for that particularly year. Therefore, if we measure the distance between these annual bands, we can reconstruct the growth history of a coral throughout its life. The incorporation of elements present in seawater into the skeleton of the corals is also influenced by changes in the environment. For example, the incorporation in strontium into the skeleton varies with temperature; therefore the changes in strontium in the skeleton can be used to reconstruct the changes in the seawater temperature through time. Similarly the amount of barium in the skeleton of corals appears to respond to changes in the amount of terrestrial runoff reaching the reef.

As part of the MaCoBioS project we are planning to analyse the growth and chemistry of the skeleton of corals from Martinique and Bonaire the Caribbean. These analyses will be used to reconstruct temporal changes in terrestrial inputs into the reef, and to determine how this is linked to land use change and pollution over time. In addition, we will investigate how different corals control their internal chemistry to facilitate the formation of the skeleton and how this mechanism responds to ocean acidification and thermals stress. For this second goal we will compare corals from the tropical Caribbean with corals from the temperate Mediterranean. These projects aim to provide managers and policy makers with better information on how corals respond to changes in their environment over long periods of time so that they can take the right steps to manage the reef and help preserve these magnificent ecosystems.

The Freie Universität Berlin team (Dr. Georg Heiß, Dr. Juan Pablo D’Olivo Cordero and Dr. Moshira Hassan) collecting a coral core in Martinique. Photo: Dr. Diego Kersting

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Blue intelligence

Blue intelligence

An ocean of data

We are living in the era of “Big data”, where the amount of data has increased and will continue rising exponentially in volume, velocity and variety. Within Marine & Coastal Ecosystems (MCEs), a huge amount of information for environmental monitoring and analysis are collected daily by satellite, aerial remote sensing tools, monitoring stations, ships, and buoys to serve marine and coastal-related sectors.

To exploit the potential of big data and overcome limitations in current mainstream frameworks, the research community has started focusing on cutting-edge Machine Learning (ML) approaches, offering a new way of looking at complex environmental systems, while providing useful predictive insight into the functioning of MCEs. ML algorithms have been applied to better understand MCEs, using an array of data types and processing methods to unravel unknown patterns and complex relationships in the data.

ML can be used to analyse the impacts of climate change (CC) on MCEs, with methods including ecological modelling  and multi-risk assessments (MRA) that allows evaluating CC risk across different sectors (e.g., fisheries, coastal and marine development, climate adaptation, and risk insurance) and marine eco-regions. 

With technological advancements, the scientific community has come to the consensus that analysing big data (including environmental, climatic, meteorological, and socio-economic data) with ML has the potential to solve real-world issues, paving the way for improved understanding and more effective management of CC risks and their interactions with the socio-ecological system.

Figure 1: Exploiting heterogeneous ‘big data’ with Machine Learning (ML) within MCEs

Boosting climate risk assessment with ML

Global warming is exacerbating weather, and extreme climatic events and is projected to aggravate risks across multiple sectors. Assessing and managing the multiple risks posed by interacting anthropogenic and natural drivers (including climate change) is one of the major challenges that the research community is currently facing.

This is particularly crucial for MCEs, where little is known about the complex inter-relationships between CC, biodiversity, and ecosystem services (ES) flow, due to limited data availability. 

The complexity of MCEs, and their spatio-temporal dynamics causes major challenges when trying to understand cumulative risks in these systems. Challenges include identifying sites at high risk of cumulative effects (hotspots), and determining the relationships and synergies between multiple pressures that may interact to cause severe impacts.

What are the competitive benefits of ML, and how it may help to better analyse and manage current and future climate change risks on MCEs?

Thanks to the current digitization of EU and international society, ML-based methods can provide an alternative approach to characterizing complex environmental systems and provide reliable quantification of the effect of human activities on MCEs along with the interacting climate-driven and local/global anthropogenic factors affecting MCEs.

ML methods can be broadly applied across different environments, (e.g., river basins, lakes, mainland, coastal areas, and urban areas), and they can be used to carry out diverse tasks while taking into account various stressors, and hazards, exposure, and vulnerability factors (e.g., climatic, economic, social, demographic, cultural, institutional, governance and environmental).

ML for MaCoBioS

Within the MaCoBioS project, we exploit the potential of ML, as well as the huge amount of data that is available for environmental observation and monitoring (e.g. remote sensing data from Copernicus CMEMS and Sentinel missions, USGS Earth Explorer, among others). ML models will be used to assess the response of MCEs to the cumulative impacts caused by CC and human activities, including resulting changes to ES capacity and flow in these systems.

We will use scenario-analysis to assess the response of MCEs under multiple ‘what-if’ multi-risk scenarios, modelled by considering different CC conditions and management strategies. Furthermore, by using worst-case scenarios, ML models can explore the resilience and tipping points of marine coastal socio-ecological systems to multiple risks.

Figure 2: Multi-tiers workflow for ML model development in the MaCoBioS eco-regions and case studies

The outputs of our ML-based applications will comprise a set of GIS-based multi-risk screening scenarios, including eco-region and local scale maps and risk metrics, simplifying understanding and communication of risks induced by changing climate and management conditions in the investigated cases. Data produced will be made available through the MaCoBioS Web-GIS Platform. This information will facilitate the identification of areas and MCEs where management actions and adaptation strategies would be best targeted, and will be used as input data for the Nature Based Solutions suitability mapping as envisaged in WP3.

Figure 3: Expected outcomes from the ML application in the MaCoBioS eco-regions and case studies

An exciting challenge ahead

The availability of spatio-temporal datasets is expected to increase thanks to the rising availability of advanced technologies for real-time environmental data acquisition (e.g., satellites, drones). This process might even be accelerated by ML optimizations in data collection and pre-processing systems. The combination of big -remote sensing- data, ML algorithms able to handle them, together with field survey data feeding validation processes, show a high predictive potential to evaluate and manage short-, medium- and long-term multiple risks due to climate change. In this sense, methods based on artificial neural networks with the use of multiple layers in the network (i.e., deep learning) could be the most promising methods, offering a higher ability to learn from data and understand highly nonlinear behaviours. Deep learning will likely be applied even more frequently to discover intricate climate, environmental and socio-economic structures in large data sets. Under the perspective of a rising abundance of data and ML models’ complexity, researchers will have the possibility (and duty) to enhance the understanding of future climate variability and risks, improving capabilities in climate forecasting, predictions, and projections, with the main aim of providing accurate and sound multi-risk scenarios that will allow for more robust adaptation planning and sustainable management of MCEs.

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EcoMagazine MaCoBioS-FutureMares

EcoMagazine MaCoBioS-FutureMares

EcoMagazine MaCoBioS-FutureMares

MaCoBioS is featured in the special issue of the EcoMagazine ( towards the United Nations Decade of Ocean Science ( The piece discusses how nature-based solutions can be a sustainable way of meeting humans’ needs while protecting and enhancing natural ecosystems. When done well, they can be powerful tools to fight against climate change and protect biodiversity. We are proud to be featured in the special issue along with the project FutureMares.(

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