The Mediterranean's vanishing underwater forests are facing an irreversible decline

Countries & Cities · Published 12 October 2026 Swipe more like this →

In short: Posidonia oceanica, the Mediterranean's most vital endemic seagrass, is disappearing at an alarming rate. These massive meadows can extend 45 meters deep, yet they have lost an estimated 34% of their area in just the last 50 years due to cumulative local stressors.

These seagrass meadows are among Earth's most valuable coastal ecosystems, providing essential goods and services. Beyond their ecological importance, they possess a remarkable carbon absorption capacity, capable of soaking up 15 times more carbon dioxide annually than a similarly sized area of the Amazon rainforest. They grow through a complex system of horizontal and vertical rhizomes, creating a terrace-like formation known as a 'kill' that traps sediment and allows them to colonize environments that algae cannot. The plant's foliage produces fibrous balls called egagropili, which wash up on shores. These structures are locally referred to as Neptune balls or the olive of the sea.

Despite their importance, the species is in significant decline. Research indicates that at least 1.5% of seagrass beds are lost every year. While the Mediterranean's P. oceanica is a primary target for marine protection—included in the European Union’s Habitat Directive as a priority habitat—the damage is often permanent. Due to their sluggish growth and minimal regeneration speeds, restoring these meadows is typically viewed as impossible within a human lifespan. The species is highly endemic to the Mediterranean Sea. Its leaves can reach lengths of approximately 1.5 metres.

The drivers of this regression are multifaceted, involving climate change factors like warming and ocean acidification, alongside direct human activities. Coastal urban development, fishing, aquaculture, and physical disturbances such as trawling, anchoring, dredging, and pipeline refilling all contribute to the decline. While managing these direct impacts can promote resilience, the slow biological pace of the plant means that conservation efforts must be proactive rather than reactive to ensure the species' long-term persistence. The plant's leaves are bright green and possess thirteen to seventeen parallel ribs. These leaves are organized into bushes containing several leaves, with the youngest located in the centre.

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