Biomasses d'ulves en Baie de Saint-Brieuc

In recent years. large quantities of green algae (Ulva sp.) had accumulated and decayed on the southern shores of the Bay of St-Brieuc (Brittany France). Maximum standing stock has been evaluated to 25 000 tons, 11 500 tons and 5 400 tons respectively for the years 1986, 1988 and 1989. Unusual low rainfall and river flow in the springtime period seem to be responsible for this observed decreased of biomass. Nevertheless, progressively increasing average concentrations of nitrogen (limiting factor) measured in terrestrial inputs may cause an enhancement of excessive growth and accumulation of Ulva in the forthcoming years. Results of a predictive numerical model validated in 1989, show that a reduction of the phosphorus inputs by 50 % might lead to a decrease of 20 to 25 % of the total biomass of Ulva.