Transplanting Posidonia oceanica: a major scientific advance for the conservation of seagrass meadows

A study has resulted in the transplantation of 384 m² of Posidonia oceanica seagrass on the scale of an industrial project as part of maritime works in Monaco. This success challenges the idea that these ecosystems are "non-transplantable". This unprecedented experiment, conducted over a period of eight years, opens up new prospects for the preservation of seagrass meadows threatened by coastal urbanisation.

As part of the construction project for the "Mareterra" district in Monaco, the marine works involved the destruction of several hectares of Posidonia oceanica meadows, an underwater plant essential to the Mediterranean ecosystem. To limit this impact, Andromède Océanologie and the University of Liège set up an unprecedented large-scale transplantation operation.

The experiment began in 2017 with the relocation of 384 m² of seagrass meadows from the construction zone to the Larvotto marine reserve. The technique used, known as "clod" transplantation, enabled the roots and associated substrate to be preserved intact, giving the plants a better survival rate. The study validated an operational technique capable of transplanting large areas of seagrass in record time, a major step forward in preserving these fragile ecosystems.

For eight years, rigorous monitoring was carried out to observe the resilience of the transplanted meadows," explains Sylvie Gobert, an oceanologist at ULiège. Despite major marine works carried out nearby, the transplanted meadow showed remarkable resilience, with health indicators rapidly approaching those of the neighbouring natural meadows." Three years after transplanting, both the transplanted and natural seagrass beds were flowering. After eight years, the surface area of the transplanted seagrass had exceeded the area initially transplanted, recording an expansion of 25.8% in 2024. "These results validate the idea that transplanting is a viable and ecologically relevant alternative as a mitigation measure in coastal development projects."

This experience is revolutionising the way in which seagrass conservation is approached in coastal development projects. Until now, the destruction of seagrass beds was considered irremediable, and compensatory measures were often limited to the installation of artificial reefs. However, this study proves that transplantation is a viable alternative that should be fully integrated into environmental conservation strategies.

Sylvie Gobert provided a scientific perspective that was essential for assessing the viability of the transplantation and ensuring rigorous monitoring of the physiological and structural parameters of the meadows.  University of Liège has leading expertise in the study and preservation of seagrass meadows, dating back to the 1970s. This long tradition of research is based in particular on observations made at the STARESO underwater and oceanographic research station, located in Corsica, in a protected marine area. For more than fifty years, this station has been studying the evolution of Posidonia oceanica meadows under natural conditions, providing unique and valuable data on their growth, resilience and ecological role. Thanks to the work carried out on this exceptional site, ULiège has developed in-depth knowledge of the dynamics of the meadows and the best strategies for their conservation and restoration. This expertise was a major asset in ensuring the success of the transplantation project in Monaco, by guaranteeing a rigorous protocol and a detailed scientific assessment of the long-term results.

The success of this experiment calls into question current practices and paves the way for better management of marine ecosystems. "By integrating transplantation as a mitigation measure in coastal development projects, it becomes possible to significantly reduce the environmental impact while preserving these precious habitats for Mediterranean biodiversity," concludes Sylvie Gobert.

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