The Black Sea is a unique marine environment. It is an enclosed coastal basin with characteristics between than of an estuary and the open ocean, with about 87% of its water mass being permanently anoxic or devoid of oxygen. The Black Sea houses a wide variety of habitat types but has a relatively low diversity of species. Historically, the Black Sea has been one of the most biologically productive regions in the world.
Specific biodiversity issues
Among the coastal basins of the world's oceans, the environmental degradation in the Black Sea is thought to be the most severe. Threats to Black Sea biodiversity are the introduction of alien species, commercial fisheries and overexploitation of resources, chemical contamination, especially from oil products, eutrophication (nutrient enrichment from plant matter) and pollution from agriculture, industry and sewage.
Most non-native species in the Black Sea have been introduced in ballast waters from shipping. Low species diversity combined with high habitat diversity in the region provides favourable conditions for invasive species, which can disrupt the stability and functioning of ecosystems and represents the biggest threat to biodiversity in the Black Sea. Eutrophication has been the main cause of the critically low oxygen levels in the Black Sea, which has led to dramatic reduction in fish catches.