A three dimensional, three-layer biological model is used to assess impact of eddy-dominated horizontal circulation on the spatial and temporal variations of plankton biomass in the Black Sea. Simulations are shown to exhibit patchy distributions of phytoplankton biomass as inferred from satellite images, and their intensities agree reasonably well with observations. Overall performance of the three layer model points to its potential capability as a practical alternative tool to more complex and computationally expensive multi-level models, without sacrificing much from the basics of the ecosystem dynamics.