Posidonia

Posidonia.

19-07-2019Manu San Félix

The Balearic Islands are blessed to have an underwater treasure: 650has of posidonia (Posidonia oceanica) seagrass meadows. This treasure is under threat from anchors and wastewater. Today we’ll talk about anchoring impacts; future articles will focus on possible solutions.

Posidonia oceanica is a Mediterranean endemic plant, which provides multiple ecosystem services. Thanks to posidonia we have transparent waters and white sand beaches. It supports biodiversity and acts as a fish nursery. It prevents coastal erosion, produces oxygen and it is a crucial carbon sink absorbing 7% of total carbon emissions of the islands. Posidonia has great ecological value and we must preserve it.

Every summer many boats anchor over posidonia meadows. Last June dozens of boats were reported anchoring over the seagrass meadow of Portals Vells; which resulted in 7 of them being fined. Posidonia meadows have been declared a priority EU habitat. It’s illegal to anchor over it. The Balearic Government is one of the very few regions with specific legislation to protect Posidonia. Other areas strongly affected by irregular anchoring are Portocolom bay, Ibiza and Formentera.

Posidonia grows very slowly; about 1 to 5 centimetres per year. Because of this, the damage caused by one day anchoring could take decades to restore. In 2017, researchers estimated that the anchor of a 15 m long boat, uprooted about 165 posidonia shoots in Portocolom; and that it would take 5 years of optimal conditions to regenerate. This single action released 915 g of carbon to the atmosphere, adding to climate change. This is just an example of how much damage a single unconscious act of anchoring on seagrass meadows can cause. Project this to the rest of the Balearic Islands, and you soon realise that action is needed now. A study revealed that Posidonia oceanica meadows in s’Espalmador (Formentera) were reduced by 44 % between 2008 and 2012, mainly because of the impact of anchoring. And then, there is the documented event of the 116m Turama boat in Formentera a few years ago whose damage will take almost thousand years to restore.

Apart from uprooting the plant, anchoring and boat activity also increases water turbidity, making it more difficult for the plant to access the light it needs to make photosynthesis and survive.

This is why badly treated water is another of the main threats to Posidonia meadows. Unfortunately, there are still several bays and Posidonia meadows across Majorca which suffer from the impacts of poor water quality. Action is also needed and urgent to address this issue and we’ll talk about what needs to be done in another article too.

The third major impact on Posidonia, is climate change. Warmer waters increase mortality of Posidonia. But if anchors and wastewater weaken the plants then Posidonia meadows are more vulnerable and less able to cope with climate change.

Protecting and recovering seagrass meadows is critical, they are our submarine forests.
Marilles Foundation advocates for action and promotes solutions to protect this priority habitat. More about this in the near future. In the meantime, if you are a boat owner please remember: anchoring on seagrass meadows is forbidden and keep 200 m distance from the coast in beaches and 50 m in rocky areas, for swimmer’s safety.