Etude expérimentale et modélisation des effets de la lumière et des sels nutritifs azotés sur la croissance d'une algue unicellulaire servant de fourrage en aquaculture intensive

INTRODUCTION For several years, intensive aquaculture has been aiming at experimentally building shortened food chain allowing commercial farming of one mollusk or fish specie. Therefore, CNEXO (IFREMER) developed several branches in its laboratories, each one starting with the growing of one or several unicellular algae which primary production was utilised to feed, either an intermediary herbivore crustacean, or directly larvae or juvenile mollusks (abalone, scallops...). A first step consisted in setting up then trivialize in vitro algal production. Now that we can benefit from routine farming, it seems interesting to move on to a second step, a more analytical one, in order to possibly optimize this type of production. The object of this DEA internship is to therefore test the adaptation capacity and growth of a unicellular alga (Haptophycea Isochrysis affinis galbana) using different lighting scenarios and nitrogened salts feeding. We will attempt to establish a simple numerical model simulating main phyto-planktonic growth processes. Furthermore, from those laboratory cultures, we can establish a close and fine follow up of rather quick (only a few hours) evolution of physiological phenomena (significant parameter modifications of cellular metabolism). Such work will allow a better grasp of some of the reactions characterising the growth of the first food chain link. As a matter of fact, this work provides data bases measured at high frequency from which we are able to calibrate short term effect modelling(high provision of nutritional salts)and to launch sub-model bases able to be integrated into a more general model which for example would simulate planktonic production (phyto and zooplankton) in a natural environment.