Functional analysis of Microcystis vertical migration:: a dynamic model as a prospecting tool.: II.: Influence of mixing, thermal stratification and colony diameter on biomass production

Yoyo is a deterministic model developed to represent the growth and vertical movement of Microcystis sp. colonies in the water column. Migration of colonies is represented in the model through the dynamics of carbon-reserve metabolism during photosynthesis and biosynthesis. It was used to quantify combined impacts of light, temperature and mixing on the growth and migration of colonies with different diameters. These 3 factors characterise a vertically non-homogeneous water column. Although conditions of simulation are schematic, they allow identification of situations in which the ability to regulate buoyancy gives Microcystis an advantage over non-mobile phytoplankton. Even if some vertical structures appear unfavourable for the exploitation of light energy, they nevertheless offer some advantages for the access to nutrients. Each diameter has particular benefits, and the increase in diameter observed throughout the year is probably an ecological adaptation to fluctuations in the environment at a seasonal scale.