In Bouin polder, one of the oyster culture zone on landbase in France, artificial substrate was suspended every week to study the variation of the biomass of benthic microalgae as the chlorophyll a. The meteorological and physico-chemical factors in sea water were studied by analysing the correlationship, correlation circle and principal component of these factors. Among the meteorological factors such as insolation, precipitation and wind, insolation was one of the most prominant factors associated with the increase of water temperature, salinity, pH and biomass but with the decrease of turbidity, dissolved oxygen and nitrate. Nitrate was the main contributor for the variation of biomass among the other nutrient components, while phosphate and silicate increased in summer when the biomass increased.