In spite of how it looks, Posidonia oceanica is not an algae – it is a plant with long, ribbon-like leaves flourishing in the oceans. Its history begins 70 to 100 million years ago, when flowering land plants colonized the ocean floor. Thus a remarkable marine ecosystem was born. It offered unparalleled services for the whole of our planet and it still continues to do so now, in the modern age. Posidonia meadows have overcome all climatological extremes since dinosaurs’ times. But now their future is at stake.

Posidonia oceanica is a species of seagrass endemic to the Mediterranean Sea. Forming underwater meadows, it creates essential living habitats for thousands of marine species. Many fish species depend on these habitats for their regular living and feeding grounds. For others, the meadows are vital reproductive areas, offering shelters to spawn and nurseries for the juveniles. 

However, providing biodiversity refuge is but one of the ecosystem services of Posidonia meadows. The other services, like carbon sequestration and coastal protection against erosion, are of no less importance. Economically speaking, the monetary value per hectare of Posidonia meadows exceeds by far that of coral reefs and the Amazon rainforest.

The Mediterranean region has over 2 million ha of Posidonia oceanica meadows distributed along its coastlines.

But over the last 50 years, we have lost an estimated 34% of Posidonia meadows. The cause of this loss is mainly anthropogenic and consists of pressures such as anchoring, pollution, and climate change. 

When seagrass ecosystems are degraded or destroyed, their carbon sink capacity is adversely affected or totally lost, and the otherwise stored carbon is released, resulting in increased emissions of CO2. It’s plain to see that the loss of Posidonia is disastrous for Mediterranean life and its biodiversity, and it irreversibly contributes to climate change.