Fish of the Black Sea

The Black Sea is stratified: an oxygenated upper layer sits over enormous anoxic depths where nothing but bacteria lives. Only its surface waters support fish. Anchovies dominate commercial fisheries. Historic beluga sturgeon (500-1000 kg) once fed Byzantine emperors caviar; today they cling to existence via strict protection. Invasive comb jellies (Mnemiopsis leidyi) crashed anchovy stocks in the 1980s, illustrating how vulnerable enclosed seas can be.