The multiple functions of Posidonia
The Mediterranean Posidonia ( Posidonia oceanica ) is endemic to the Mediterranean Sea and the most common seagrass species in these waters. It covers between 25,000 and 50,000 km2 of coastal areas, corresponding to 25% of the seabed at a depth of between 0 and 40 m. Posidonia plays a key role for marine life but also for the preservation of our beaches, where we wear our ethical swimsuits .
More than half of the oxygen we breathe comes from the sea. Posidonia is called "the lungs of the Mediterranean" because it is one of the most important sources of oxygen supplied to coastal waters. According to a study by the Mediterranean Institute for Advanced Research (IMEDEA) and the BBVA Foundation, the Posidonia present in the Mediterranean produces 14 to 20 liters of oxygen per square meter every day .
The Posidonia herbarium has many functions:
- Dried Posidonia leaves were traditionally used in Mediterranean countries as packing material for transporting fragile items of glassware and pottery, as well as for shipping fresh fish from the coast to cities.
- Posidonia grows in large meadows that cover the seabed and create an ecosystem of great beauty, making possible leisure activities such as scuba diving (in eco-responsible swimsuits) .
- Posidonia habitats also play an important role as carbon sinks. They absorb carbon dioxide, store carbon at an average rate of 83 g C/m² per year and help to mitigate the effects of climate change.
- Posidonia helps stabilize the seabed, break up swells and waves, and encourage the deposition of sedimentary particles.
- Posidonia dead leaves, which can form clumps more than 2 meters high and up to 20 meters wide, also form compact and resistant structures along the banks. These natural shields provide very effective protection against beach erosion , so that you can always enjoy the sand and the sun (in an ethical swimsuit).
Role of Posidonia in the protection of beaches against erosion
A recent survey on the management of seagrass beds stranded along Mediterranean beaches reveals that more than 80% of coastal municipalities remove the beds before the summer season, despite the many benefits that these beds bring to the maintenance of beaches and coastal ecosystems.
The survey was carried out in the summer of 2017 in 144 Mediterranean cities in Spain, France, Italy, Greece and Cyprus to discover current beach management practices and tools. She revealed that the removal of Posidonia deposits is a common practice on most Mediterranean beaches, driven by the aesthetic demands of the tourism sector in the region. A practice which is however harmful to the beaches.
Indeed, Posidonia is a marine plant that forms vast underwater meadows in the Mediterranean Sea. During winter storms , its leaves and roots are washed ashore and often form thick layers mixed with sand, called benches . In spring and summer, however, these banquettes are often removed by local governments in response to heavy pressure from coastal tourism and to please bathers. Yet the banks of Posidonia play an essential role in protecting beaches against erosion and in supporting vulnerable ecosystems - such as coastal dunes - which are protected by European legislation.
"Little is known about beach management and the consequences of certain practices, however, we do know that the deposits formed from Posidonia seagrass beds act as a shield that prevents the loss of sand from the beach , providing resilience and the stability of the beach.With the Interreg project 'Posbemed', we aim to understand current practices in Mediterranean European countries and to raise awareness among beach users and managers of the benefits of this natural capital by providing tools to improve management," said Maria del Mar Otero , marine expert at IUCN's Center for Mediterranean Cooperation .
“We are trying to prove that seagrass leaves found on the beach are good and should be kept in place, as they help restore sand, fight coastal erosion and make beaches livelier” , affirms in turn Maria Eugenia Giunta Fornasin , of the Interdepartmental Agreement for Mosquito Control of the Mediterranean Coast .
Each of us can also contribute to preserving the beaches and the environment in general by taking eco-responsible actions, such as, for example, preferably buying an eco-responsible swimsuit !