Photo courtesy of Manu San Félix
The crystalline waters around Ibiza and Formentera are one of the islands' main attractions. Indeed, sometimes the sea is so turquoise, you could be forgiven for thinking you'd been transported to the Caribbean. But did you know this is mainly thanks to a very special plant that is often mistaken for seaweed?
Named after the ancient Greek sea god, Posidonia oceanica (to give it its full, scientific name), is a type of seagrass found all over the Mediterranean. However, the meadows around Ibiza and Formentera are some of the best examples of their kind. So much so that in 1999, they were declared a UNESCO World Heritage Site.
The meadows stretch, quite literally, for miles. One particular patch off Formentera was found to be 15 kilometres long and, in 2012, scientists studying specimens from it revealed they believed it to be between 80,000 and 100,000 years old, making it among the largest and oldest living organisms on the planet.
The lungs of the Mediterranean
Posidonia is vital to our marine ecosystem, supporting a variety of species, including fish and sea horses, which use it for feeding, breeding and shelter. Not only that, it is also a highly effective carbon sink. Scientific studies have shown that seagrass meadows have much higher long-term carbon burial rates per square metre than tropical forests, such as the Amazon. In posidonia meadows, this carbon can be locked away in seabed sediments for centuries or even millennia, making them a key natural ally in the fight against climate change.
The plant also filters the water, trapping sediments to improve water quality and clarity, as well as producing oxygen via photosynthesis. For this reason, it is often referred to as the “lungs of the Mediterranean”.
Under threat
Despite being one of our most valuable natural assets, posidonia is in danger. Across the Mediterranean, Posidonia oceanica meadows are estimated to have regressed by about 34% over the last 50 years.
The warming of the seas due to climate change poses a major threat, as Posidonia starts to suffer adverse effects once the water temperature reaches 28°C. This is something that is now happening over extended periods in summer, as revealed by annual monitoring of the sea temperature in Talamanca Bay, carried out by local environmental group GEN-GOB and financed by Ibiza & Formentera Preservation.
The same study also measures the coverage and density of Posidonia in Talamanca and other points around the island, and has found some areas in which more than 50% of the meadow is dead and shows no signs of recovery.
This is not just down to rising sea temperatures but also factors such as increasing pollution in the water and uncontrolled boat anchoring. Posidonia oceanica grows incredibly slowly, at a rate of around one centimetre a year. Just one vessel dropping anchor in the grass can create a bald patch, which can take decades or even centuries to repair.
With around 2000 recreational charters estimated to cross between Ibiza and Formentera every day during the season, it’s easy to see how even just a small percentage discharging their waste at sea or anchoring in the meadows can cause extensive and lasting damage.
Our Blue Crime Classroom is a new project, run in conjunction with Jaume I University in Castellón, which seeks to shed light on illegal practices such as these by studying their impact on our marine environment and promoting policies to improve its protection.
Preventing erosion
Even when dead, Posidonia still fulfils an important function, its brown leaves protecting coastal areas from erosion. For this very reason, the leaves that cover the shoreline in many parts of the island are removed by town halls from the more popular beaches during the summer months, allowing people to enjoy the sand.
They are then put back in the winter, in order to provide a natural shield against storms and prevent beaches from being washed away.
What you can do
We all need to play our part to ensure this magical plant is able to thrive in our waters. Even if you are just visiting the island briefly, you can still do your bit to help:
- If you’re going out on a boat trip, please ask your captain to ensure they don’t anchor in posidonia. The free Posidonia MAPS app for iPhone and Android, can help guide them. Eco-moorings should be used where available.
- Ensure that wastewater is not discharged overboard; special containers are provided in the ports for this purpose.
- Invest in environmentally friendly, “reef-safe” sunscreen. Pollutants from normal sun cream contaminate the water and can damage the seagrass.
- Become a Posidonia ambassador and help spread the word about this precious plant and how best to protect it.
- Donate to our Posidonia protection work via our website below.
You can find out more about Ibiza & Formentera Preservation and donate towards their work by going to their website: ibizapreservation.org. You can also follow them on Instagram, Facebook and LinkedIn.
