This carbon sink is 15x more powerful than the Amazon

This carbon sink is 15x more powerful than the Amazon. And you've probably swum over it.

Posidonia oceanica (“Neptune grass”) is unique to the Mediterranean. It:

• Absorbs CO₂ 15x faster than the Amazon (per hectare)

• Locks carbon away for 1,000+ years

• Produces 10x the oxygen of a mature tree

If intact across the Mediterranean, it could absorb up to 42% of the annual CO₂ output of all Mediterranean countries combined.

Yet, we've lost up to 50% of it in just 50 years.

Why?

1. Pollution: Runoff feeds algae that blocks the sunlight it needs.

2. Warming seas: Summer heatwaves above 26.6°C kill the grass.

3. Yacht anchors: Posidonia grows just 1–2 cm a year. A single 50m yacht anchor can destroy 1,500 m² in seconds.

The fight back is on! The EU ARTEMIS project is replanting it in Crete, and groups like Aegean Rebreath are installing eco-moorings.

But there's a glaring gap. France, Spain, and Croatia enforce strict anchoring bans with fines up to €100,000.

Greece still has no national ban.

Why?

Sources

• Octopus Foundation / Kosamare – drone survey (2022) on Posidonia coverage and carbon (15x Amazon, 42% CO₂, 1,000-year storage); also Journal of Biological Research (2024) and Moeve Global / Oceana

• IUCN Med / Biological Conservation (Telesca et al.) – up to 50% coverage lost in 50 years (2014)

• Marbà & Duarte, Global Change Biology – 26.6°C temperature threshold (2010)

• Mediterranean Posidonia Network – 50m yacht anchor destroys 1,500 m²; 1–2 cm/yr growth

• iSea / Ionian Environment Foundation – drone survey (2024): >50% of boats anchoring on Posidonia in the Inner Ionian

• Interreg Euro-MED – ARTEMIS restoration project, Crete (2025)

• TP Greece / Aegean Rebreath – eco-moorings (2026)

• AnchorGuardian.com; EUobserver – France, Spain and Croatia anchoring bans with fines up to €100,000 (2025)

• EUobserver – “Mediterranean's hidden forests under siege by tourism” – Greece has no national anchoring ban (December 2025)