Background The endemic Mediterranean seagrass species Posidonia oceanica (Neptune grass) forms dense and extensive underwater meadows with leaves that can reach 1m in length. These rare seagrass meadows (listed as a priority for conservation according to the EU Habitats Directive) provide important ecological services and support a highly diverse community, including species of economic interest. However, when Posidonia meadows decompose, as part of their natural life-cycle, a residue is washed ashore that causes a disagreeable smell. Thousands of tonnes of beached Posidonia oceanica are collected by coastal communities each year, and disposed of in landfill sites. As well as the high cost of cleaning and disposal, there is a lack of guidelines on how to effectively manage this biomass material. Moreover, the heavy machinery used to remove seagrass residues along sandy coastlines can cause considerable damage to coastal ecosystems. Objectives The objective of the P.R.I.M.E. project was to develop the reuse of Posidonia oceanica residues through an integrated management system. The project aimed to reduce the environmental impact of the removal of the beached residue and to reduce the costs related to its disposal, principally through its reuse as compost for local agriculture. The project involved all concerned stakeholders, including local authorities responsible for coastal areas, bathing establishment directors, beach users, municipal waste disposal services, compost producers and agricultural companies. Results The P.R.I.M.E. project established an integrated management system for beach Posidonia oceanica residues, taking into account marine ecosystem issues and the potential reuse of these residues in agriculture. The project identified methods of residue recovery and methods for utilising the collected organic biomass material to produce compost as fertilisers. This was achieved through a participatory multi-stakeholder approach, mainly involving policymakers (local, regional and national), compost producers, beach resort managers and agriculture companies, and the implementation of knowledge-gathering, pilot study, demonstration, training and dissemination activities. The project consolidated and assessed available knowledge about the management, monitoring and mapping of seagrass meadow residues and other stranded biomass around the Mediterranean. This involved gathering a large amount of data for an economic analysis, including dynamic and qualitative aspects of biomass accumulations, collecting methods employed, and the costs of removal and disposal. Posidonia meadow residues were collected, washed, cut-up in situ, and transported to five pilot sites, where physical, biological and chemical parameters were characterised, to help define best practice methods for low-impact residue removal and pre-processing. Two different pre-processing approaches (involving grinding and drying) were assessed; while, in parallel, three prototypes were designed and set up ("Rotative wash de-sanding prototype", "Bio-grinder prototype" and the "Dryer prototype"). Demonstrative activities at the pilot study sites included Life Cycle Assessment (LCA) of the identified management system. The Dryer prototype was used to demonstrate the agronomic use of green compost from Posidonia residues in greenhouse cultivation or as soil amendment. The results of demonstrative tests also showed that seagrass residues could be reused as compost in a range of other applications (e.g. nursery production of horticultural plants, organic agricultural fertiliser, and as soil amendment for urban green areas). The project provided training for administrators and technicians of local authorities and private companies on the eco-sustainable management of stranded Posidonia. Specific outputs of the project included a database for information on beached biomass management and compost production processes, a map of Posidonia meadow locations, and a report on methodologies for monitoring these meadows and their residues. The project developed a DSS (Decision Support System) for the management and use of beached biomass residues ("software PRIME"), which enables the identification of best practice through a list of questions relating to the beaching phenomena. This software assesses and quantifies the collection, treatment, storage and transport phases related to the management of beached biomass. In addition, the project published national and international manuals for the recycling of beached biomass residues in coastal dune reclamation and restoration; guidelines for the valorisation of beached biomass residues that balance environmental protection with tourism; and the creation of a register of 78 technicians certified for the sustainable management of beached Posidonia residues. The project ideas have been taken up by interested stakeholders. For instance, at least three of the five industrial composting plants in Puglia are now engaged in the composting of Posidonia residues, while numerous municipalities and entrepreneurs have expressed interest in applying the strategies promoted by the project (in Puglia, Toscana, Sardinia and Sicilia). The reuse of Posidonia residues leads to a decrease in the costs for their disposal. More specifically, surveys have shown that in Italy 50% of beached biomass reaches landfills, with municipal authorities bearing all the costs (70-80 €/tonne), with an average expenditure of about 140 000€ annually. If, on the other hand, 50% of this is used for compost, the costs borne will be related only to transport. When considering the Regional Plan for Urban Waste Management (updated 2013), on average, the transport costs represent about 36% of the total costs spent by the provinces in the Puglia region. Choosing the compost alternative will thus help them save 65% of the costs related to beached biomass disposal. The project demonstrated that rather than being an environmental problem, integrated management can turn beached seagrass residues into a useful resource for agriculture. Further information on the project can be found in the project's layman report and After-LIFE Conservation Plan (see "Read more" section).