A coupled plankton–anchovy population dynamics model assessing nonlinear controls of anchovy and gelatinous biomass in the Black Sea

A coupled model of lower trophic levels and anchovyEngraulis encrasicolus ponticuspopulation dynamics was developed to analyze the mechanisms controlling sharp anchovy and gelatinous zooplankton biomass transitions from the 1960s to the 1980s in the Black Sea. An increase in anchovy stocks from estimated low (~300 kt) to moderate (~700 kt) in the late 1960s was related to weakening piscivore predation pressure, slight nutrient enrichment of the basin during an early eutrophication phase, and competitive exclusion of gelatinous carnivores. The transition to high stocks (~1500 kt) from 1979 to 1980 was caused by additional nutrient enrichment. With enhanced enrichment, gelatinous carnivores started to coexist with anchovy at low biomass levels (