Functional analysis of Microcystis vertical migration: A dynamic model as a prospecting tool

YOYO is a deterministic model intended to represent the growth and vertical movements of Microcystis colonies in the water column. The fluctuations of the carbohydrate content in cells are submitted to the influence of photosynthesis and biosynthesis. They modify the colony density, which responds through a vertical movement of migration. The model simulates, at a daily scale, the fluctuations of Microcystis density resulting from the dynamics of the carbohydrate reserve metabolism during photosynthesis. A sensitivity analysis is carried out, under constant conditions of light, temperature and colony diameter, in order to identify the effect of light and temperature on the metabolism and migratory behaviour of colonies with different diameters. State equilibria, reached under permanent regimes of light and temperature close to culture conditions, are consistent with experimental results from the literature. A periodical light forcing is then applied, for one temperature and a large range of diameters. Simulations point out that migrations are characterised by a pair amplitude/period of the movement, which depends on the diameter. The migratory behaviour highlights an ecological advantage linked to the colony diameter.