Posidonia: the queen of crystal clear seas in the Balearic Islands

Thank you Posidonia... for that mixture of turquoise blues and greens in transparent waters that provide a relaxing, magnificent view. You have been the seal of identity of the Balearics sea for decades. You also appeared on a number of adverts, postcards, photos showing holidays, sea trips and more... a sublime mixture showing all the biological activity happening under the sea.

Posidonia is unique to the Mediterranean

Posidonia Oceánica only lives in the Mediterranean Sea. Its morphology and reproductive capacity astonish many scientists, which is why it has been declared a World Heritage Site. Only in some areas of Australia has a species with similar, but not equal characteristics ever been seen.

Long live Posidonia

Although it looks like a seaweed, it is a very long-lived plant. Posidonia meadows can live up to 60 years. One of the most extensive is found between Ibiza and Formentera and it is estimated that posidonia can measure up to 8 km. Its history dates back to the beginning of its existence on the mainland, is over 100,000 years old, although it has managed to adapt to the rise of the sea until it has managed to survive under it, maintaining its roots, stem and flowers.

Oxygenating our waters

The oxygen quality of the water is increased by Posidonia, which makes its underwater meadows a perfect place for numerous species to live. Releasing tons of oxygen in some of the largest areas of the Mediterranean. When looking for light, Posidonia’s stems grow vertically generating spaces where many species can take shelter from the hard sand bottoms where only the strongest survive is implacable. This generates an increase in biodiversity and an exceptional oxygenation of the water, which leaves behind landscapes like those that the fortunate people of the Balearic Islands are accustomed to seeing.

A plant that is increasingly loved

Like all good love stories, that of the Balearics and Posidonia has been growing over time and more and more people are conscious of this unique plant. Those who know the true value do not mind seeing it on the beaches, or in the depths of the ocean. On the contrary, in the Balearics we know that without it, this beautiful sea would lose its identity which is why we will always support and encourage conservation.

Interested in finding out more? We interview Marcial Bardolet, Technician in charge of the Posidonia Surveillance Service of the Balearic Nature Institute (IBANAT.

What is Posidonia and where can we find it?

MB: It is a Mediterranean plant, which appears like a meadow occupying the entire coast of the Balearic Islands. There are many beneficial properties for the environment. Posidonia is one of the most extensive and oldest plants, genetically dated at 100,000 years.

Can this plant be found outside the Mediterranean?

MB: Oceanic Posidonia can only be found in the Mediterranean. However, there are other types of Posidonia like phanerogams, which we can find in Australia, but there are not many with this typology. Yes, we can find other typologies in various places with underwater prairies that are also plants. But really, like the oceanic posidonia, there is no other.

Is there a difference between Posidonia oceanica and algae?

MB: Posidonia is a plant that, unlike algae, has roots, fruits and flowers. This plant shows that it was out of the sea many years ago. It was occupying the land surface and for some reason it went back into the sea and is able to breathe there. It is a simpler typology and at an ecological category level it is at a more advanced level than algae.

Why is this plant in danger of extinction?

MB: It suffers from several threats, the most relevant are:

The increase in sea temperature

Discharges into the sea

Illegal Anchoring Practices

How does Posidonia affect the environment?

MB: It is a jewel for the sea fulfilling vital functions, such as the clarity of the water on the beaches that surround the whole of the Balearic Islands, it helps to make the water transparent.

It absorbs CO2 - much more than a tropical forest, it generates oxygen and creates the perfect habitat for thousands of marine species. Another very interesting point is that Posidonia is also capable of generating sand.

Posidonia is vital in order to continue having beaches with beautiful and transparent waters, full of life. In order to keep being able to fish, we also need posidonia.

What is the life cycle of this plant?

MB: We are used to seeing it in summer. In autumn, the leaves reproduce and we can see its green flowers which become fruit in spring (sea olives). These olives float and when they rot, some fall down and help to plant seeds, generating more of the posidonia plant. In summer it loses its leaves which turn brown, these brown leaves reach the beach in autumn and help to keep the sand there.

How deep do Posidonia plants grow?

MB: It is found all along the coast, they can be found at 0 metres (there are some Posidonias that reach the surface). All the way down to 40 metres, usually between 0 and 30 metres. They usually cover very sandy areas.

The largest meadows we have in the Balearic Islands can be found in the bay of Alcudia, Pollensa and Formentera / Ibiza. There are giant Posidonia meadows of about 650 km2 .

Do you think that yachts and boats give enough importance to this plant?

MB: Fortunately, the contact we have with the captains of the boats is very good. As lovers of the sea they do not put up any opposition to good practices and good treatment of Posidonia, we all know that it is a win/win.

We have to help the boats that come to enjoy our beautiful seas to provide tools to the captains, so that they can simply see a map and avoid it. Or they can use applications to differentiate where the sand is, and avoid posidonia. This way everybody wins.

We have a service called Posidonia Surveillance Service where large vessels can call on the VHF channel, they can consult information about where we are, some cartography or the applications that exist on the market on the website: posidonia.caib.es

Why have you decided to study these plants?

MB: Sometimes life takes you down a path and I have been lucky enough to be able to protect Posidonia. My part is not so much scientific studies, about what Posidonia is, but rather the management of how to protect it. In other words, to do this you also need to know it, obviously I must have knowledge of how its ecology works and I am passionate about that, but also what is needed in the end to protect it is how you manage the impacts and that is what I have been working on for 13 years.

I started with a European project called life posidonia, where a lot of studies were done and from there, I had the opportunity to get on that big boat called Posidonia. Now we continue to help protect them.

Is there an increase for the care of Posidonia?

MB: Posidonia is already included in European directives, in the laws of the Spanish Ministry for example the Ministry of Ecological Transition, as a protected species.

The most specific laws that are being made about its protection are in France. From 24 metres upwards posidonia is protected from impacts on anchoring. Since July 2018 we have had the protection that is an autonomous decree and that exists in the Balearic Islands. At the same time, we can also say that we are getting ready to have cartography and to give sailors the tools so that they can anchor well.

How do you think we can take care of Posidonia in future?

MB: There are many useful apps to use such as the one from the Balearic government or PosidoniaMaps and DONIA APP.

With these applications you can find out where the Posidonia meadows are and if they will be affected by anchoring. You can check the appl whilst on the boat and see the cartography. Simply press the button and it indicates if it's a good place to anchor or if you could damage the Posidonia.

This is a good tool, so that sailors can anchor with peace of mind and know that they are not making any impact on the areas they’re enjoying.

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