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n other words, without Posidonia Oceanica, there would be no sand, and the water wouldn't be as transparent as it is because this marine grass filters out sediment. Last but not least, Posidonia Oceanica acts as a natural breakwater, slowing down the waves that break on the coast with less force, carrying less sand out to sea. In winter, the dead leaves of the seagrass that accumulate on the beaches prevent the sand from blowing away. A researcher of the Balearic Oceanographic Centre (Institut Espanyol d’Oceangrafia), Biel Jordà, has shown that without Posidonia Oceanica, winter storms would be as devastating as Gloria in 2020. Posidonia Oceanica meadows are threatened by boat anchoring eutrophication and warming waters. Their mortality increases when sea temperatures rise above 28°C.

Another major factor is the concrete development of the coastline. “We've mismanaged the coastline. By building hotels, ports and marinas on dunes, we've altered the natural dynamics of the beaches. A beach is a living system that includes a part that is submerged and a part that is immersed and extended by dunes," Vaquer explains. Building on dunes blocks sand movement. The sand from the dunes does not compensate and therefore, does not maintain the balance of the beaches. 

This is the case at S'Arenal, where the northern beach has shrunk since the construction of the port and marina, which trap sediment. Es Trenc, which was protected from urbanization projects in the 1970s, is now suffering the effects of human use. The retreat of the sand is particularly striking in heavily frequented areas: near the parking lots of es Cremat (Na Tirapel), the beach has lost almost 19 metres. Since 2020, the GOB association has been calling for the closure of this parking lot, singled out as one of the causes of erosion.

Overcrowding is a major factor. Every visitor unintentionally takes a few grams of sand with them, either clinging to their skin or trapped in a towel. Santanyí town council has calculated that Caló des Moro, which because of its fame on Instagram attracts 4,000 tourists a day, loses 50 kg of sand every day. At just 14 metres long, this natural gem could disappear long before the sea submerges it.

According to forecasts by researchers of the Mediterranean Institute for Advanced Studies (IMEDEA), the surface area of Balearic beaches could be halved by the end of the century. Three quarters of the sites, such as Peguera, Cala Fornells and Ca'n Pere Antoni, could be temporarily submerged by storms.  And the most vulnerable, such as Cala Formentor or Calo des moro, could disappear for good.

For a long time, it was thought that the trend could be reversed by re-injecting sand pumped from the sea onto the beaches. “A costly, temporary and ineffective solution,” Raquel Vaquer assures us: “The most important thing is to protect and conserve the Posidonia Oceanica.” This marine plant, essential to beach stability, also captures 7% of the archipelago's greenhouse gas emissions: a key ally in the face of climate change.