Esther Garcés i Pieres, 1998

Dinoflagellate blooms are sometimes regarded as accumulations of slow-growing ungrazed populations. Thus, the blooms would appear not to be the end result of high cell division rates but of interactions between the physical environment and specific strategies of organisms. There are few studies that present serial in situ growth rate measurements during major temporal events such as dinoflagellate blooms, since spatio-temporal monitoring of such events is extremely difficult. Growth rate measurements tend to be discrete values collected at discrete sampling locations, whereas to provide a better idea of the population dynamics, there should ideally be a series of measurements. The main objective of this thesis is measure the in situ potential growth rate of the most important blooming dinoflagellates (toxic and non toxic) in the Catalan Coast (Alexandrium minutum, A. taylori, Ceratium furca, Dinophysis sacculus, Gymnodinium pulchellum and Gyrodinium corsicum) in field conditions. The estimated growth rate by cell cycle is used in this study to measure the in situ potential growth rate. Diffusion-based incubation methods in which there is water exchange between the inside of culture containers and the outside environment have been employed to obtain the in situ net growth rate. In the general population dynamics other biological process must take in to account. The study of the specific strategies (vertical migrations, phototaxis, mucus formation, cell aggregates, resting stages in the life history) of the dinoflagellates (Alexandrium minutum, A. taylori, Ceratium furca, and Gyrodinium corsicum) is also presented to understand the observed distribution patterns of dinoflagellates blooms in the field.