Eléments nutritifs limitant la biomasse phytoplanctonique d'une lagune tropicale de Côte d'Ivoire. Comparaison des méthodes d'estimation

"In vitro" enrichment experiments on natural populations have been used to determine the nutrients controlling the potential biomass of phytoplancton in the Ebrié coastal lagoon. The limiting nutrients were generally nitrogen, phosphorus and carbon, in this order ; in three cases out of eleven, P and N act simultaneously ; in an extreme eutrophication case, N, P and C were all limiting. No effect was observed following addition of metals, vitamins or chelators. The limitations deduced from the enrichment experiments show a. good agreement with the elementary composition of the external medium ; in waters potentially limited by N alone, the dissolved inorganic nutrients have a N : P ratio lower than 25. The agreement is poorer when the sestonic N : P ratio is used. The limits of application of these various results in lagoon Ebrié are discussed.