How does marine life in the Black Sea compare with marine life in the Mediterranean Sea?

Marine life in the Black Sea is significantly less diverse than in the Mediterranean Sea, primarily due to the Black Sea's unique physical characteristics. While the flora and fauna of the Black Sea largely originated from the Mediterranean through a series of historical invasions, the two seas differ sharply in biological richness.1

A defining constraint for the Black Sea is its lack of oxygen below depths of approximately 230 to 500 feet (70 to 150 metres). This hydrogen sulfide-rich zone is essentially lifeless, which limits the habitat available for marine organisms. Consequently, the diffusion of sea-bottom (benthic) plants and animals in the Black Sea is four to five times poorer than in the Mediterranean. Similarly, while the Black Sea hosts a variety of microorganisms and about 750 species of phytoplankton, its zooplankton population is notably smaller, consisting of only about 80 species.21

In contrast, the Mediterranean Sea supports a much higher diversity of marine biota, with nearly one-third of its approximately 12,000 species being endemic, despite its own challenges with nutrient scarcity.3