Symbol of Six-Fours-les-Plages, a seaside town on the French coast located in Var, the seahorse has disappeared from the "lagoon" of Brusc – actually a lagoon closed off by a posidonia reef. The cause: the collapse, in the early 2000s, of the cymodocea seagrass that structured the entire ecosystem. On September 27 and 28, the Hippo-Campus festival brought together residents, scientists, and institutions to assess the situation and accelerate restoration, with a simple goal: for biodiversity to become rich enough to welcome back the iconic animal. A very local experience, but enlightening for the entire Mediterranean
By Olivier Martocq - journalist
IA Index: Library of Mediterranean Knowledge
The seahorse, a sign of the restoration of biodiversity in the Mediterranean
22-med – October 2025
In Six-Fours-les-Plages, the Hippo-Campus festival mobilizes residents and scientists to restore the lagoon of Brusc.
The hoped-for return of the seahorse illustrates how science, institutions, and citizens are rebuilding a fragile Mediterranean ecosystem.
#mediterranean #biodiversity #seahorse #ecosystem #lagoon #france
Festival organizer, Vincent Bellingard, a French professor, embraces a method: “The environment is a societal issue: everyone is concerned. Using emotion and humor to convey a rigorous message, supported by science and institutions, is the best way to act.” The seahorse, “Poseidon’s horse” in ancient tales, is an umbrella species: “To bring it back, we must first restore the habitat and biodiversity. Our horizon is the 30 hectares of seagrass in the lagoon.” Throughout this festival, scientists and representatives from various public and private organizations involved in the project “a bit crazy, to reintroduce this disappeared animal.” took the stage.
A unique lagoon… and brutally degraded
Marine biologist at the Paul-Ricard Oceanographic Institute – located on one of the islands of the lagoon – Sylvain Couvray recalls the uniqueness of the site: “One of the largest posidonia barrier reefs in the world closes the bay and protects a very shallow body of water. Inside, a meadow of cymodocea dominated.” In two years at the beginning of the 2000s, “more than 99% of the seagrass disappeared, replaced by a sandy expanse.” After ruling out overpopulation and occasional pollution, researchers blame “a profound modification of the sediment, notably due to sand deposits for beach nourishment.”
Since the cessation of these pressures (prohibitions in the lagoon, transfer of boats to the port), patches of seagrass have reappeared. Transplantations have succeeded, “but it’s slow: around 5% of the initial surface.” A complementary avenue: reintroducing holothurians, “sediment engineers,” to enrich the soil and accelerate recovery. “It’s like putting earthworms back in a forest: we naturally enrich the substrate to help the seagrass.” Olivier Brunel from the Oceanographic Institute of Monaco draws a parallel with the noble pen shell (Pinna nobilis), a giant bivalve endemic to the Mediterranean, once omnipresent: “Protected since 1992, the species had been recovering… until the arrival, in 2016, of a parasite that decimated almost 100% of the populations in open sea.” Refuges remain in lagoon environments, and pathways are emerging: resistance genetics, breeding, and replanting resistant individuals. “The first published genome of the noble pen shell comes from an individual from Brusc,” he points out. Proof that local knowledge can inform Mediterranean responses.
Another essential but underground project to undertake is combating pollution. “The recipe is clear,” explains Pierre Boissery, a marine expert at the Rhône-Mediterranean-Corsica Water Agency, “for an environment to function, quality water is needed. In the Mediterranean, this requires efficient wastewater treatment plants, oversized compared to the discharges from local populations, as they must be capable of absorbing tourist flows.”
A chain of actors for a house to rebuild
To simply summarize what is happening in Brusc, Vincent Bellingard chooses the image of a construction site where everyone holds a brick: science, management, funders, the state, citizens. “Like a house, there needs to be a project manager and skilled trades. In the lagoon, without habitat, the fish leave.” France being a champion in terms of administrative layers and agencies for implementation, reconstructing this ecosystem involves many actors.
At the French Office for Biodiversity, Élodie Damier situates the legal framework of this marine area labeled Natura 2000. “The Natura 2000 network consists of a set of natural sites, both terrestrial and marine, aimed at ensuring the long-term survival of particularly threatened species and habitats, with high conservation stakes in Europe. The goal here is to preserve the posidonia seagrass (about 75% of the site), the barrier reef, coralligenous areas… as well as animals like the Common Dolphin.” Actions focus on knowledge, awareness, and visitation with strict rules to follow: “Navigation, anchoring, swimming, and diving are prohibited in the lagoon; offshore, we deploy anchoring zones and light equipment to avoid anchoring in the seagrass.” Among the latest tools for the general public is Nav&Co, a mobile app that displays regulations and environmental points of interest: “It’s serious, as it is informed by the managers of the various Natura sites.”
Another involved actor, the Coastal Conservatory has made Brusc a demonstrator. Fabrice Bernard, director of international cooperation, reminds us that “If the French coast retains green windows, it is thanks to acquisitions protected since 1975 ‘for everyone and forever.’ Here, the example is remarkable: the municipality, Paul-Ricard Institute, Conservatory, and Water Agency have managed to plan and finance pilot operations.” The site has even received a UN label as a specially protected area of Mediterranean interest.
Regulate without opposing
In daily life, this translates into active co-management of the island of Grand Rouveau and its maritime public domain. “Two eco-guards are stationed there in summer to promote good practices — no anchoring in the seagrass, no fires, no camping, respect for paths.” Sometimes, it is also necessary to combat invasive species. Caroline Illien, the director of heritage management at the Conservatory, recalls the battles fought against the black rat and the uprooting of witch's claw to favor the return of local species.
Ensuring compliance with laws and regulations, the maritime prefecture adopts a protection line that is “both firm and practicable.” For André Grosset, “Natura 2000 advocates for the sustainable development of activities: we do not exclude, we frame. After the anchoring orders for vessels over 24 m on posidonia, we are now working with local authorities and users to regulate small boating — buoys, dedicated zones, credible alternatives.” Other projects include regulating the observation of marine mammals (“swimming with them is prohibited”), controlling noise nuisances from vessels, and likely in the future, light projected during night anchoring. “Our decisions must be scientifically supported and socially accepted,” concludes the deputy head of the “Protection and Sustainable Management of Marine Space” at the maritime prefecture of the Mediterranean.
It remains to sustain efforts over time: accelerate the recovery of seagrasses (substrate, holothurians, targeted transplantations), manage visitation, equip compatible anchorages, maintain prohibitions in the lagoon, and educate tirelessly. “We have turned off the stress taps; it is up to us to maintain the resilience dynamic,” summarizes Sylvain Couvray. And the scientist connects reason and emotion: “Convincing people to act makes the environment a matter of the heart.” Participatory science also brings signals of hope: last year, a juvenile seahorse was observed in Brusc. “Cousins,” the syngnathids, have reappeared: there is no reason the seahorse should not return.
Cover photo: Sergiu-Jacob- Pexels