The first Spanish group of experts on blue carbon ecosystems (G3ECA) has been created with the aim of protecting aquatic coastal vegetation. Blue carbon refers to the CO2 that is sequestered by coastal ecosystems, basically seagrass meadows, mangroves and salt marshes. Although they cover less than 2% of the sea surface, they bury up to 50% of marine carbon in their sediments and can retain it for millennia. We talk to Miguel Ángel Mateo, a CSIC researcher at the Centre for Advanced Studies in Blanes (CEAB) and coordinator of G3ECA together with Fernando Brun (University of Cádiz).
Miguel Angel Mateo, in the centre of the picture, working with his team a few days ago in the sampling of seagrass meadows in Portlligat (CEAB-CSIC)
G3ECA was created with a dual objective: to assess public administrations about the role of these ecosystems and their implications for national strategies in the fight against climate change, and to advise, support and carry out conservation and restoration projects, involving the private sector in the mission. The existence of voluntary carbon markets, where such projects could be monetised through the certification of carbon credits, opens a way for this.
Miguel Angel Mateo has been sampling these days with his team (the Aquatic Macrophytes Ecology Group; game-csic.com) the Posidonia oceanica meadows in Portlligat, the iconic cove of Cadaqués (Cap de Creus, Girona). Perhaps that is why the conversation almost inevitably turned to seagrass meadows and Posidonia.
It is estimated, Mateo explains, that every year ‘between 1 and 7% of seagrass meadows are lost worldwide, which is equivalent to hundreds of thousands of football pitches’. According to 2020 data from the United Nations Environment Programme (UNEP), seagrass meadows cover some 300,000 km2 worldwide; and some 1,619 square kilometres in Spain, according to the ‘Atlas de las praderas marinas’ (Atlas of seagrass meadows).
In the case of posidonia meadows, annual losses in the Mediterranean could be around 1%, although, Mateo points out, this is a very difficult figure to establish due to the lack of studies on an important section of its coasts.
'Every year up to 7% of the world's seagrass meadows are lost, which is equivalent to hundreds of thousands of football pitches’
What have you been doing these days in Portlligat?
We have been working on the development of a new methodology to inventory the amount of blue carbon stored under the bay's seabed, within the framework of the European project Effective. To this end, we are collaborating with the company GPA-Seabots, which is providing the project with several autonomous floating drones capable of mapping the soil and subsoil of the bay with unprecedented speed and precision. In addition to the inventory, these developments will make it possible to monitor the evolution of the meadows more frequently and less expensively, as well as to assess the impact of anchors on the meadow, prior to the installation of ecological buoys.
How did this think-tank come into being and how would you define it?
It is a natural consequence of the expansion of this line of research, which has grown exponentially over the last decade. The group arose from the evidence that there is a good critical mass of blue carbon experts in Spain and that joining forces can help to obtain better results. We have recently applied for a Research Network from the State Research Agency with the aim of formalising this group and improving our capacity to inform public administrations and companies on everything related to blue carbon, from inventories to carbon markets.
We are currently 30 members, specialists in very diverse areas ranging from basic science to socio-economics and carbon markets. G3ECA is therefore defined as a multidisciplinary group with a vocation to offer solutions to help conserve our coastal natural heritage and thus mitigate climate change, while contributing to economic growth and the wellbeing of society.
What actions can the private sector take in this field with your help?
Mainly actions to achieve greater protection of blue carbon marine ecosystems and, in some cases, to restore them. By taking part in these actions, companies not only can offset part of their CO2 emissions and help mitigate climate change, but also contribute to fulfilling their corporate social responsibility strategies and enhancing their reputation. Specific examples of actions would be the installation of ecological buoy fields in tourist areas with a high incidence of anchoring of recreational boats on seagrass meadows, the recovery of desiccated marshes or abandoned salt marshes, or the replanting of mangrove forests. Thanks to the existence of voluntary carbon markets, this protection and restoration could be monetised through the certification of carbon credits, helping to finance part of the cost of the actions.
By taking part in these actions, companies not only can offset part of their CO2 emissions and help mitigate climate change, but also contribute to fulfilling their corporate social responsibility strategies and enhancing their reputation.
How do you calculate a price on this CO2 sequestration capacity? It does not seem easy
For better or worse, the concrete function of carbon capture and storage by blue carbon ecosystems is easily translatable into an economic value. Each tonne fixed by these ecosystems, following a restoration action, or each tonne no longer emitted from them, following a protection action, has a price defined by the voluntary carbon markets, subject, like any market, to the laws of supply and demand. What is neither easy nor economical is the implementation of restoration or conservation projects, nor the subsequent certification of the effectiveness of such projects in order to achieve certification of carbon credits. This is especially true for seagrass because it is submerged.
Are there further actions that the private sector can take with you? I am thinking, for example, of reducing the impact of activities that damage the seabed, such as trawling.
In addition to those mentioned above concerning ecological anchoring and the recovery of salt marshes and mangroves, one of the objectives of the group is to discuss internally possible actions that could help the conservation of blue carbon ecosystems. These would be aimed at habitat protection and enhancement, such as improving the transparency of coastal waters. It is possible to envisage the diversity and potential of actions that can be taken to protect our coastal ‘blue heritage’.
With regard to trawling, it should be noted that it has been the biggest culprit in the destruction of seagrass meadows in Spain in the past, and still is in many parts of the Mediterranean and other seas around the world. Although trawling has been banned in Spain for years at depths of less than 50 metres [seagrass beds are found at depths of up to 40 metres], it is still practised illegally in some communities. Once a meadow is destroyed, the loss is virtually forever, as it takes decades to centuries to recover.
Even if the destruction of grasslands due to illegal trawling practices could be documented, given that their avoidance is an obligation by law, even if the obligation could be enforced and the destruction stopped completely, it would be considered a ‘non-additional’ avoidance of emissions, and therefore not eligible for certification as carbon credits. The most effective way to combat illegal trawling is to install biotopes that hinder trawlers' manoeuvres.
Studies indicate that seagrass meadows remove between 0.8 and 2% of the CO2 we humans emit each year, which does not seem very high. That doesn't sound like a very high percentage. Can you put it in context?
The context is no more and no less than that. Of the total annual global emissions, terrestrial ecosystems (forests and soils) capture 29%, the oceans 26% and the remaining 45% accumulates in the atmosphere. Of this 26%, blue carbon ecosystems are responsible for a small part. While this is not an exorbitant percentage, we cannot afford to lose this sequestration capacity. And it is very important to remember that CO2 capture and storage is just one of the many other ecosystem services that blue carbon ecosystems (BCEs) provide us with, including protection from coastal erosion, being a focus of biodiversity, a filter for pollutants, or the basis of food chains on our coasts.
What are the impacts of the disappearance of Posidonia meadows?
The destruction of Posidonia meadows must be considered virtually irreversible. Re-stocking practices are effective in some cases, but always extremely costly. This means that their implementation cannot be envisaged for large areas. The impact is very high.
The economic value of each hectare of Posidonia that is lost is very complex to establish, with estimates ranging from tens of thousands to millions of euros. The loss of associated services includes the reduction in catches of species of commercial interest, the increased vulnerability of our coasts, such as buildings, promenades, railways or beaches, as well as the loss of water quality and tourist attraction, such as clear waters and white sands. There is also a worsening of global warming, as there is a reduction in carbon sequestration capacity and the re-emission of millennial CO2.
The loss of services associated with seagrass meadows includes the reduction in catches of species of commercial interest, the increased vulnerability of our coasts, such as buildings, promenades, railways or beaches, the loss of water quality and tourist attractiveness (...). There is also a worsening of global warming, as there is a reduction in the capacity for carbon capture and the re-emission of millennial CO2.
Robots used to monitor seagrass meadows, in the last sampling in Portlligat, last August. Image: CEAB-CSIC.
Has the extent of blue carbon ecosystems lost annually been counted?
Despite the exponential increase in interest and effort in studying blue carbon ecosystems, there are still large areas of the planet with no information on the abundance or even the presence of these ecosystems. For example, almost half of the Mediterranean coastline is believed to have little or no studied seagrass distribution and abundance, particularly at depths not visible to drones and satellites.
The latest estimates suggest global loss rates over the last 20 years of around 0.28% and 1.58% for salt marshes and mangroves, respectively. For seagrass meadows, the estimate is more complicated and is as high as 7% destruction at the end of the 20th century. It has also been estimated that between 20% and 30% of all seagrass cover on the planet has been lost since the early 18th century. Since the 1980s, in the case of Spain, the marine plant species most affected has been Cymodocea nodosa, with loss rates of between 10 and 15%. Zostera nolti is reported to have experienced a slight recovery, between 1 and 2%. Posidonia has experienced a net decrease of just over 1%, and stability or recovery is being seen in more and more places, undoubtedly thanks to protection laws and awareness-raising efforts by biologists and conservation associations. Unfortunately, in the previous 40 years (from 1960 to 2000), between 13 and 50% of its total area had been lost, an area that will take a long time to recover. In all likelihood, one of the main causes would have been trawling.
In the case of salt marshes in Spain, 60% of their area has been lost since the beginning of the 19th century. As they were considered unhealthy areas, they were drained and, in some cases, urbanised or salt pans were created. They are now stable or recovering, with the aim that at least 50% of the remaining ones will have improved by 2030.
How do you monitor this loss?
The evolution of the extent of salt marshes and mangroves is monitored using aerial images (both from low altitude and from satellites).
Monitoring in the case of grasslands is more complicated and costly because they are submerged ecosystems. At certain depths, observation by optical systems is not possible. The evolution of grassland extent is studied by comparing the extent and density of the habitat from one mapping campaign to the next. Since the deep meadow boundary is particularly vulnerable to coastal water deterioration, it is common practice to mark this boundary and measure whether the meadow is advancing or retreating in relation to this boundary from one year to the next. We do this by diving.
New and more accessible technologies, such as aerial drones, satellites, or floating and submersible drones, equipped with sonar, photography and video systems, are making the work much easier than in previous years and will allow more frequent, accurate and less costly monitoring of seagrass meadows, marshes and mangroves.
“Nowadays, only around the 8% of our seas has been protected”
It is said that we cannot know what pristine marine ecosystems were like. If you consider restoring ecosystems to their original state, what would be the goal?
Pristinity is a rhetorical concept if it is not given a frame of reference. It is defined as ‘first, primitive, original’. When we talk about ecosystem restoration, we must focus on achievable goals that ensure functionality and resilience, i.e. we must decide to what former state we aspire to return the ecosystem. In general, this ‘virginity’ or pristinity is understood as a state prior to significant human impacts. For practical purposes, the goal is usually to recover the area of ecosystem lost through identified anthropogenic causes or catastrophic natural events. It has been estimated that protecting 30% of our planet would allow the damage to the rest to be repaired.
Tell me about some of the group's more immediate projects.
The most current activity of our group focuses on two recently initiated European projects. One is the European Coastal Blue Carbon, funded by the European Space Agency. In this project, GAME is responsible for making available our extensive published and unpublished database on blue carbon stocks in seagrass and saltmarsh biomass and soil in Spain and in some areas of the rest of the Mediterranean, as well as their accumulation rates. We will use Regression Boosted Tree models to obtain spatially explicit maps of blue carbon storage in Spain and France, initially. This project ends in 2027.
In the Effective project, our group is leading the objective of three-dimensionally mapping seagrass meadows to inventory blue carbon stocks using autonomous floating and submersible vehicles equipped with surface and sub-surface acoustic probes. The work, in pilot mode, is being carried out in the bay of Portlligat, in Cap de Creus. This project ends in 2026.
Mercè Fernández / Comunicación CSIC en Cataluña
Learn more:
Spanish group of experts on blue carbon ecosystems (G3ECA) https://g3eca.com/
Recent trend reversal for declining European seagrass meadows https://www.nature.com/articles/s41467-019-11340-4
Protecting the 30% of the planet. “Why we’re committing to 30 x 30”. https://www.nature.org/en-us/what-we-do/our-priorities/protect-water-and-land/land-and-water-stories/committing-to-30x30/
Effective project: “Potenciando el bienestar social y la prosperidad económica mediante el refuerzo de la gestión de la protección y la restauración de áreas marinas protegidas mediterráneas.” https://effective-euproject.eu/
European Coastal Blue Carbon project https://esa-coastal-blue-carbon.eu/