Reinforcement of carbon sinks in the marine environment by G.I.S Posidonie

The RenforC project is one of the winning projects in the 2020 call for projects by the setec Foundation to combat climate change in France. It is supported by the “Groupement d’Intérêt Scientifique pour l’environnement marin, en particulier des Posidonies”, also known as G.I.S Posidonie.

The G.I.S Posidonie is an association of scientists whose main activities are based on the acquisition of knowledge about the marine environment, the scientific development of this knowledge, and assistance with the conservation, restoration and management of the marine environment.

The project

Posidonia: the lung of the Mediterranean under threat

Posidonia, also known as Mediterranean tapeweed, is a seagrass species located at low depths in the Mediterranean Sea. In addition to being a refuge for many marine animals, Posidonia meadows act as carbon sinks that fix carbon underground during their slow growth, a few centimetres per year. In Corsica, they cover 60% of the seabed between 0 and 40 metres deep and, like an underwater lung, have accumulated 15% of the carbon in the air over the last 4,000 years. Its exceptional characteristics make it an essential species in the fight against climate change.

However, human activity is disrupting this balance: in addition to the pressure exerted by climate change, the anchoring of pleasure boats in these coastal waters is uprooting the meadows over several metres and destroying biodiversity in a significant way.

Since 2020, the anchoring of boats longer than 24 metres has been prohibited in the Bouches de Bonifacio natural reserve. It was following this action that the RenforC project of the G.I.S Posidonie was able to be set in motion to try to repair the damaged environment.

The RENFORC programme

The G.I.S Posidonie’s RenforC (Reinforcement of carbon sinks in the marine environment) programme consists of replanting seagrass beds using cuttings in the Gulf of Sant’Amanza in Bonifacio, Corsica.


It is divided into four phases:

Phase 1: The organisation of a seminar for the presentation of the project to the partners and above all the sharing of transplantation protocols between the four project partner intervention teams – THALASSA Marine research & Environmental awareness (France); Biosurvey (Italy); Instituto Mediterráneo de Estudios Avanzados (Spain); the International School for Scientific Diving “Anna Proietti Zolla” (Italy)


2023 review seminar ©G.I.S Posidonie


Phase 2: The setting up of scientific expeditions during which cuttings are taken upstream and replanted in the damaged areas by the 4 teams. Annual monitoring of the meadows is then planned after the experimentation with the goal of scientifically comparing the performance of the different techniques used by each team.

Not only would this programme allow the restoration of an essential ecosystem, but it would also contribute to scientific progress in this field by comparing different transplantation methods.


 April and June 2021 expeditions: Removal of cuttings and transplantation of the herbarium. ©G.I.S Posidonie

Phase 3:  Experimentation with an additional protocol based on cuttings harvested from wrecks instead of transplants taken from the herbarium, in order to study the influence of the transplants’ origin.

Phase 4:  Monitoring of the experiments continues with the addition of factors such as carbohydrate measurement, leaf length and growth rate. This enables us to assess the vitality of the cuttings.

A search for Posidonia blooms was carried out in parallel.


Other experiments

Other experiments have included the planting of posidonia seeds, supported by the setec Foundation. Flowering is rare, occurring only every 10 years. Parallel experimental projects were carried out at Sant’Amanza and Taverna.




How has the project progressed so far?

The first phase of the project took place in April 2021, during which a seminar to present the project and share knowledge was organised with all the partner members, including the setec Foundation.

This was very quickly followed by the start of the second phase: a first field expedition was carried out by the THALASSA Marine research & Environmental awareness team in April, followed in June by the three other teams from Biosurvey, the Instituto Mediterráneo de Estudios Avanzados and the International School for Scientific Diving. All used different transplantation methods, as explained above. A total of 12.500 seagrass cuttings were planted during these expeditions. The growth of the plants is monitored by the scientists throughout the implementation of the project.

As of october 2022, two dives were organized to follow the evolution of the experimentation: a first one in july 2021, and a second one in may 2022. These dives allowed the team to collect information to gather intermediate results, that can be observed in the following table:



In September 2023, a seminar was held to review the progress from 2021 to 2023. Initial encouraging results were noted, with a high survival rate for cuttings. The ultimate aim is to compare the protocols with the reference zone on all these parameters to assess the impact of climate change and heat waves on Posidonia meadows. Carbohydrate sampling and analysis are carried out after heat waves to assess carbohydrate reserves before the winter period. This is linked to carbon sequestration capacity.

Monitoring continues, and discussions are underway on regulations governing access to and use of the sea by boats.

The role of the setec Foundation

The setec Foundation is providing financial support to the G.I.S Posidonie for all of its activities. At the end of the 2020 call for projects on “Fighting climate change in France”, it committed to allocate a total of 20 000 euros to the organisation in order to carry out the programme.

Rigorous monitoring is also organised throughout the year following the awarding ceremony, during which reports on the progress of the project are exchanged to ensure that the missions are carried out properly and that the association’s needs are being covered. RenforC is one of the flagship projects supported by the Setec Foundation in 2020 and represents an essential contribution to carbon neutrality and the ecological transition.

Marine engineers from setec in vivo (a subsidiary of the setec group) are providing voluntary support to the project by sharing their expertise with G.I.S Posidonie at each stage.

In 2022, the Foundation decided to renew its support for a new experiment involving the transplanting of cuttings from shipwrecks.

Then in 2023, the setec Foundation helped finance the experimentation of different techniques for planting Posidonia seeds.


To know more about the G.I.S Posidonie, go on their website or France Bleu.

Download the article on the RenforC project published in the magazine TRAVAUX (November 2021) of the Fédération Nationale des Travaux Publics (FNTP)

Download the article on the RenforC project published in Le Point (May 2022).

Download the article of the project published in Corse Matin (2023) : Corse-Matin_20230915