Background The Natura 2000 site Arrábida-Espichel is located just south of Lisbon, on the west coast of Portugal. The site was classified as an SCI due to the high marine biodiversity of the area, including more than 1 100 marine species of fauna and flora. Seagrass meadows in the site guaranteed shelter and food to the juveniles of many species of marine fauna, giving it a nursery role similar to many estuaries. However, in recent years, these non-estuarine Zostera marina meadows and their associated biodiversity had been almost totally destroyed. The main threats have been illegal fishing practices - such as dredging for bivalves - and the anchoring and mooring of recreational boats. Seagrass formations in what was the last truly marine example of this habitat on Atlantic Iberian Coastlines fell from 30 ha in 1983 to 0.006 ha in 2006. A management plan was approved in 2005, which regulates all activities for the area, including fishing and recreational boat numbers. However, the regeneration of meadows was prevented by the lack of natural seagrass recruitment possibilities within the site. Further obstacles included the lack of awareness amongst both the local and visiting populations of the importance of the habitats and their needs. Objectives The Biomares project proposed an active management strategy for reefs and the restoration of sand banks permanently covered with sea water - Habitats 1170 and 1110 respectively under the EU Habitats Directive - at the Marine Park Site Arrábida-Espichel. It aimed to reverse the existing tendency for overexploitation and damage to habitats. The project specifically sought to restore the lost seagrass meadow at Portinho da Arrábida. This challenging objective was to be achieved through the planting of seagrasses in the target area. Seagrass would be harvested from donor populations. However, it would also be important not to overly stress the donor sites through excessive harvesting. Therefore the project also aimed to cultivate seagrass by sowing seeds on the target site and propagating seagrass shoots in laboratory, which could also be planted. These different approaches would help achieve the additional goal of establishing genetic diversity in the restored habitat. Results The project successfully conducted the preparatory actions for habitat restoration of Zostera marine meadows. It gathered marine data and raised awareness of local stakeholders that will be extremely important for the future management of the SCI. However, the hoped for re-establishment of the seagrass habitats was even more challenging than had been anticipated and was not ultimately successful. The project assessed the available area and genetic diversity of donor populations. An extended search resulted in a full assessment of cover distribution and conservation status of the seagrass habitat along the Portuguese coast. It identified the four most appropriate areas for harvesting donor plants and three areas for collecting seagrass seed covering different species. The team conducted four annual surveys of key marine data using techniques including seabed acoustics, sediment analysis, net fishing for marine life samples and seabed videoing. These generated a marine ecosystem characterization and cartography covering the project area to a depth of 100 m. They also developed quantitative spatial models to estimate the time required for total recovery of a continuous seagrass meadow based on examination of patch dynamics for different planting densities of specific species. A key focus of the project was engaging with fishing and leisure-boat activities. Specific studies characterised the fishing fleet, trends in fishing activity and the opinions and expectations of fishermen. Several tons of underwater cables were removed from old moorings in the project area and substituted by around 100 environmentally friendly mooring buoys. However, plans to install a floating dock to protect the seabed further remained unfulfilled by the end of the project due to bureaucratic delays. The oceanographic museum created dedicated space and materials for laboratory work and diving support. The team conducted seagrass germination experiments with varying temperature, salinity, sediment and light to find the optimum conditions. However, not enough seeds grew to the seedling state to allow their use as a donor population. Nor was the direct sowing of seeds on the seabed successful, with no germination observed. The flowering shoots of seagrass from donor populations were harvested and a pilot transplanting activity conducted. Three pilot sites were found to be unsuitable because of strong water currents, unsuitable sediment and port harbour usage. Despite the creation of 62 pilot plots, with a total of 5 276 plant sods across 7 ha, survival was very low with major threats seeming to be storms and predation from fish. Further information on the project can be found in the project's layman report (see "Read more" section).