A one-dimensional coupled physical-ecosystem model identifies factors causing blooms of the coccolithophore Emilania huxleyi in the Black Sea, regularly observed during the early summer periods. The model specifically applies for a more idealized ecosystem of the interior basin, away from the coastal zone. It is represented in the form of four groups of phytoplankton (diatoms, dinoflagellates, E. huxleyi, a small phytoplankton group), and two groups of zooplankton further accompanied by simplified nitrogen and phosphorus cycles. The simulations show that the internal trophodynamic conditions in the Black Sea support E. huxleyi bloom development during May-July period as a part of the seasonal phytoplankton succession. They start flourishing after the diatom and dinoflagellate blooms under nitrogen depleted and moderate light conditions. They make use of regenerated nutrients available in the surface mixed layer and grow concomitantly with picophytoplankton community in the subsurface levels. (c) 2005 Elsevier B.V. All rights reserved.