• impact of rhizome harvesting
• impatto della raccolta dei rizomi
• Posidonia oceanica (L.) Delile
• success of transplantation
• successo del trapianto

The endemic Posidonia oceanica (L.) Delile is a dominant seagrass species in the Mediterranean Sea. It provides important ecosystem services such as protection from coastal erosion, substrate stabilization and nursery for numerous organisms. It promotes nutrient cycling, supplies raw materials, and supports carbon storage by sequestering carbon and releasing oxygen, which enhances water quality. However, P. oceanica is threatened by several stressors, including direct human disturbance (e.g., anchoring, trawling, pollution, eutrophication, sediment accumulation) and global warming.
For these reasons, P. oceanica meadows are declining in some areas, while thriving on others. Reforestation interventions are increasingly recommended by various European directives to compensate for the loss of the seagrass in critical areas. There are several reforestation techniques available, such as growing rhizomes in the aquarium, planting seeds using fixation systems, directly securing plant fragments to the substratum, anchoring rhizomes with artificial supports, and transplanting cuttings in protective nets or cages. Most of these techniques require "cutting transplantation," involving the transfer of plant fragments from a donor meadow to a recipient site.
Following a reforestation intervention carried out in July 2023 on the island of Giannutri, two different experiments were carried out. The first one aimed at identifying the least invasive way of collecting shoots for transplantation and the second one aimed at identifying the factors that influence the success or failure of the transplant.
In the first experiment, conducted in July 2023 at Punta Secca (Giannutri Island), we compared the effect of collecting rhizomes of P. oceanica at the edges or in the middle of donor meadows. It was hypothesized that disturbing the meadows at the edges would have more detrimental effects on the seagrass compared to collecting rhizomes in the middle, since water motion during storms should have greater impacts at the margins of the meadows, amplifying harvesting effects. It was also hypothesized that differences between positions (margin vs. middle of the meadow) would increase with the intensity of disturbance – i.e. the number of shoots collected.
The second experiment was conducted in June 2024 at Cala dello Scoglio (recipient meadow), using rhizomes collected from two donor meadows (Cala Brigantina and Punta Secca). We examined whether the success of reforestation depended on the characteristics of the origin and donor sites. Since reforestation interventions inevitably involve exposure of the collected rhizomes to multiple sources of stress, including detachment from the substratum, transportation (sometimes involving aerial exposure) and relocation to a different place, it is important to assess the vulnerability of the seagrass to any of these disturbances.
Preliminary results from the two experiments indicate that collecting rhizomes from the middle of the donor bed can mitigate subsequent impacts compared to harvesting at the edge and highlight the importance of the characteristics of the destination site in determining the success of a reforestation intervention. Reducing exposure of rhizomes to stressful conditions, such as aerial exposure during transportation, can also increase the chances of success. These results help identifying best practices to guide future reforestation practices, contributing to reverse the loss of a slow-growing species such as P. oceanica.