A recurrent and localized dinoflagellate bloom in a Mediterranean beach

A recurrent, prolonged and singular bloom of Alexandrium taylori Balech in an open beach (La Fosca, Spain, NW Mediterranean) is described. Alexandrium taylori appears at several places along a wide area of the NW Mediterranean (Costa Brava) during the summer, reaching concentrations up to 105 cells l–1, but it only proliferates persistently, massively (densities >106 cells l–1) and recurrently during August in La Fosca beach. The A.taylori bloom can be considered a manifestation of large-scale proliferation in a restricted area, where coupling between resting cysts in the sediment and bloom outbreak is not a major factor compared to the interaction of local environmental conditions with the planktonic organism's life history. From observations of environmental conditions (the environmental window) and the multiscale spatio-temporal distributions and life history of A.taylori, we describe the bloom dynamics and answer some critical questions about the different phases of the bloom. Some of these answers are: (i) the source of the A.taylori population is widespread offshore and is not located directly at the beach; (ii) high cell densities are reached and maintained with a moderate in situ growth and low loss rates; (iii) temporary cysts act as a reserve of the population.