The Black Sea

The Black Sea is one of the most enclosed and vulnerable marine basins in the world — connected to the rest of the ocean only through the narrow Bosphorus Strait, with an extremely slow rate of water exchange. This is exactly what makes it so sensitive to pressure arriving from land: pollution from nutrients and plastics, rising water temperatures, and accelerating coastal erosion.

A Sea Split Into Two Worlds

One of the most unusual things about the Black Sea is that below roughly 150–200 metres, the water is essentially devoid of oxygen — one of the largest permanently anoxic water bodies on the planet. As a result, almost all life in the sea is confined to a thin surface layer, and it is precisely this narrow “habitable” band that bears the full weight of pollution, fishing and warming. Any additional pressure on this narrow layer affects the whole ecosystem disproportionately.

Pressure on the Ecosystem

Studies of long-term data show that the Black Sea ecosystem has passed through different states over recent decades — from a relatively balanced food web in the 1960s, through severe eutrophication and the collapse of fish populations in the late 1980s, to partial stabilisation in the 1990s. These abrupt transitions show how quickly pressure from fishing, pollution and invasive species can overturn a sea — and how slowly it recovers.

Six Countries, One Basin

The Black Sea is shared among six coastal states, and its catchment area covers parts of more than twenty countries — rivers such as the Danube, the Dnieper and the Don drain almost the whole of Central and Eastern Europe into it. Pollution released thousands of kilometres inland reaches the Bulgarian coast carried by these rivers. Protecting the Black Sea is therefore fundamentally a regional task, not only a national one.

What We Monitor

We track a combination of indicators — water quality, the spread of microplastics, the increasingly frequent marine heatwaves (periods of unusually high surface water temperature), and the rate of erosion along Bulgaria’s Black Sea coast. This information feeds into our analysis and our position on policy at national and regional level, including under the Marine Strategy Framework Directive and the Bucharest Convention on the Protection of the Black Sea.