Snorkel almost anywhere off Ibiza and you will pass over dark green meadows swaying in the current. That is posidonia, and the clear water around it is no coincidence.
Posidonia is a flowering plant, with roots, leaves, flowers and fruit, that returned to the sea long ago. It grows only in the Mediterranean.
Its floating fruit is sometimes called the olive of the sea.
From a boat it looks like a dark shadow under the surface. Underwater, it is a field of ribbon-like leaves up to about a metre long, moving with the swell, with fish darting between them.
The meadows trap sediment and release oxygen. They slow the waves, hold the seabed in place and give young fish somewhere to hide.
Without them, the water would be cloudier and the beaches thinner.
Scientists describe posidonia as a blue carbon habitat: the meadows store carbon in their roots and in the thick mat of dead material beneath them, which can build up over very long periods if left undisturbed.
Without the meadows, the water would be cloudier and the beaches thinner.
In autumn, dead leaves wash up and form thick banks on some beaches. They can look untidy, but they protect the sand from winter storms.
Many beaches now leave them in place outside the summer season.
The balls of fibre that wash up, sometimes called sea balls, are made of old leaf fibres rolled by the waves. They are harmless and part of the same natural cycle.
A meadow can be a single plant spreading by cloning over a very long time. One study estimated that some Mediterranean meadows are tens of thousands of years old.
The meadows between Ibiza and Formentera were included when UNESCO listed the site in 1999.
Posidonia grows only a few centimetres a year. An anchor and chain dragged across it can tear out a patch that took decades to grow.
A Balearic decree regulates anchoring over the meadows, and mooring buoys are installed in some bays in summer.
Mooring buoys are being installed in more bays, and there are mobile apps and charts that show where meadows lie. The rule of thumb is simple: if the seabed is dark, keep the anchor up.
Choose boat trips that anchor on sand or use buoys. Snorkel without standing on the seabed. Leave the leaves on the beach.
And if you hire a boat, learn to tell pale sand from dark meadow before you drop the anchor.
The best places are calm, rocky coves where the meadow comes close to shore. Float face down, breathe slowly and let the swell carry you; there is no need to stand.
Look for cuttlefish hovering over the leaves, wrasse and bream moving through, and fan mussels standing upright in the meadow. Fan mussels are protected and have been badly hit by disease, so admire them without touching.
Posidonia grows only in the Mediterranean, and meadows have declined in many places because of coastal building, pollution and anchoring. Where they are protected, they can hold steady or recover slowly.
The meadows between Ibiza and Formentera are among the best preserved. That is why they are part of the UNESCO listing, and why the rules on anchoring are taken seriously.
The easiest place to see the meadow without a boat is the south. Ses Salines Natural Park, declared in 2001, covers the south of Ibiza, the north of Formentera and the sea between, and the shallow water inside it holds posidonia close to the shore. Salt is still harvested here. From the low walls around the salt pans the water shows its depth by colour: pale over sand, darker where the leaves begin.
The salt pans are a Ramsar-listed wetland, and the shallow lagoons behind them work because water moves freely between sea and shore. That same exchange keeps the water clear and low in nutrients, which is what posidonia needs. Walk the paths between the pans early in the day, when the light is better for looking at the water and the heat has not yet built. Birds use the lagoons most in migration seasons.
West of the pans, the small Phoenician settlement at Sa Caleta sits on a low headland, and the beaches at Ses Salines and Es Cavallet back onto dunes and juniper. These are public places inside the same protected area, and all of them depend on the same clean water. The natural park office can say which paths are open and where the protected zones begin.
Posidonia holds sand. Its rhizomes, woody stems that creep slowly across the seabed, knit into a mat that traps sediment and fragments of dead leaf. Over a long time that mat builds into a structure with height to it, and the structure takes energy out of the swell before the swell reaches the beach. Ground that loses its meadow loses that buffer as well.
The mat is sometimes called matte, and it is a record of the meadow's own growth, laid down slowly, year on year. An anchor chain dragged through it cuts a furrow that may take a very long time to close. Sand that was held in place shifts, and the beach behind begins to lose what the meadow had been keeping.
This is why the shape of an Ibiza cove is not only about rock. Meadows grow from the shallows down to about 30 to 40 m, as far as the light allows. Where the shelf is wide and shallow, the meadow is wide too, and the water above it stays clear and pale. What looks like a beach is partly a piece of biology holding its position.
The meadows read from above as dark patches in bright water, and they are easiest to pick out from high ground when the sun is high and the surface is calm. Cliff paths on the south-west coast give that view. Look for the edge where dark green turns to turquoise, which is roughly where the leaves stop and sand begins.
Water temperature is typical rather than guaranteed: about 18-19 °C in May, 22-23 °C in June, 25-26 °C in August, 23-25 °C in September. A thin wetsuit makes the shoulder months comfortable. Much of the seasonal business closes roughly from November to April, and there are fewer flights and ferries. The quiet months suit walking the coast and looking at the water rather than swimming far.
The ferry from Ibiza Town to La Savina crosses the channel that the UNESCO listing of 1999 describes: the posidonia meadows and coastal ecosystems between the two islands. The fast crossing takes about 30 to 35 minutes, and the water below is part of a World Heritage Site. Check operators for timetables, which thin out in winter, and ask the natural park office about rules inside the protected area.
No. It is a flowering plant with roots, flowers and fruit.
It keeps the water clear, shelters fish and protects beaches. It grows very slowly and is easily damaged.
Yes. Just don't stand on it or anchor on it.
Dead leaves wash up in autumn and protect the sand from storms.
Yes, the meadows were included in the 1999 listing.
The largest expanse lies in Ses Salines Natural Park, off the south coast and across the water towards Formentera; the UNESCO listing covers this stretch. Snorkelling from beaches inside the park shows the shallower beds, and the ferry to La Savina crosses the deeper ones. Visibility is best on calm days, and much of the seasonal business around the park closes roughly November to April.
Anchoring over the meadows is regulated by a Balearic decree, and mooring buoys are installed in some bays in summer. Where no buoy is available, anchor over sand rather than seagrass, and check the current rules with the natural park office or the port authority before setting the anchor. The rules change, so confirm them for the bay you plan to use.
Meadows grow from just below the shoreline to about 30-40 m deep, so the dark patches seen from a cliff or from a boat are usually seagrass rather than rock. The shallowest beds lie close to the beaches inside Ses Salines Natural Park, where a mask and calm morning water are enough to see them clearly.
The meadows trap sediment, oxygenate the water and help hold the sand that builds the beaches, which is part of why the coast between Ibiza and Formentera was listed by UNESCO in 1999. The salt pans at Ses Salines are still worked and the wetland is Ramsar-listed. Cloudy water in a bay can simply reflect that day's wind and swell.
Photo credits: Peter Drier, CC BY 2.0, via Wikimedia Commons.
Half a minute of Ibiza, from the old town of Dalt Vila to the coves and headlands of the coast.
Captions are built in; the transcript is on the Ibiza page.
Video: JUAN CARLOS NAVALON SANCHEZ, Steven HAuse, Haseeb Ahmad, Josh Tavernier, Boris Ivas, Luca Musella on Pexels
