Stoichiometric variations of NI P , C and O 2 during a Gymnodinium catenatum red tide and their interpretation

The chemical parameters 'NO', 'PO' and 'CO' are constants that remain invariable during photosynthesis or remineralization of organic matter. Nevertheless, exceptionally, during a red tide these parameters are no longer constant. Their vertical variation during a Gymnodinium catenatum red tide in the Ria de Vigo, Spain, in October 1986 is described. Stoichiometric equations are obtained for biomass synthesis in the superficial water layer and in the nutricline which are adjusted to the experimental data. From these chemical parameters a new parameter 'NCO' is calculated which remains constant in both normal phytoplankton populations and dinoflagellates endowed with vertical migration and differential synthesis of cellular compounds. With this parameter, the oxygen loss to the atmosphere during the red tide was estimated and a good fit was found with that calculated from the diffusion. This permits the calculation of net accumulated production. From the same parameters, the vertical transport of nutrients produced by the migration of the dinoflagellates is quantified. A good agreement with the spatial distribution of total nitrogen (organic and inorganic) is obtained, if the carbohydrate consumption in respiration is taken into account.