Frequently Asked Questions on the Mediterranean deep sea
The Mediterranean Sea is on average around 1,500 metres deep. Its deepest point — at 5,267 m depth — is the Calypso Deep in the Ionian Sea, off the coast of Greece.
The deep sea starts at around 200 metres depth, where sunlight is no longer sufficient for photosynthesis. More than 80% of the Mediterranean seafloor lies within this zone.
Yes, the Mediterranean is home to coral reefs, but not the tropical kind most people picture – rather cold-water coral reefs.
Cold-water coral reefs grow in complete darkness, up to thousands of metres below the surface. They do not need sunlight or warm temperatures and feed by filtering particles from ocean currents.
These reefs form complex habitats that support fish, crustaceans, and other deep-sea species.
The main protection currently in place is a ban on bottom-contacting fishing, such as bottom trawling, below 1,000 m depth, adopted by the General Fisheries Commission for the Mediterranean (GFCM) in 2005.
In waters shallower than 1000m, bottom trawling is permitted across much of the Mediterranean, including in areas where some of the most ecologically important and vulnerable deep-sea habitats occur – namely between 600 and 1,000 m depth.
Oceana is calling for the bottom trawling ban to be extended from 1,000 m to below at least 800 m to effectively protect these habitats.
Deep-sea ecosystems are home to an abundance of marine life, making them biodiversity hotspots. Further, species like cold-water coral reefs and sponge grounds provide nursery and feeding habitats for commercially important fish and other species, thus supporting fisheries.
Deep-sea habitats store significant amounts of carbon, mostly in seafloor sediments, for centuries or millennia, thus playing a key role in regulating our climate. However, when disturbed by destructive activities, like bottom trawling, this carbon can be released as CO₂ back into the ocean, undermining the ocean’s climate regulation role.
Deep-sea species and habitats are also long-lived and slow-growing, making them highly vulnerable to physical disturbance. Recovery is extremely slow — if it happens at all — so damage can persist for decades or centuries.
Yes, the Mediterranean is one of the most overfished seas in the world. According to latest data (2025) from the General Fisheries Commission for the Mediterranean, around 52% of assessed fish populations in the Mediterranean and Black seas are still overfished. Overall fish populations have declined by more than a third over the past 50 years in the Mediterranean, and by around 50% in the Western region and the Adriatic Sea.
As coastal populations decline, industrial fleets are moving into deeper waters, increasing pressure on fragile deep-sea habitats. Effective fisheries management must address both fish populations and the ecosystems they depend on.
The Mediterranean is under intense pressure from climate change and human activities. The sea is warming faster than the global ocean average, and its semi-enclosed nature means pollution accumulates more easily. Further, around 150 million people live along its coasts, adding additional pressure from tourism, fishing, shipping and coastal development. The Mediterranean is at the same time a major biodiversity hotspot. Although it represents less than 1% of the global ocean, it is home to 4%-18% of marine species, including many endemic species found nowhere else.
Protecting the Mediterranean is therefore essential for restoring biodiversity, increasing ecosystems’ climate resilience, ensuring food security and supporting coastal economies.
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