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14th International Conference on Harmful Algae, 1-5 November 2010, Creta, Greece.-- 3 páginas., Epiphytic dinoflagellates of the genus Ostreopsis have been related to harmful episodes in many Mediterranean coastal areas since 1998: respiratory difficulties, fever, and skin irritations affected people exposed to marine aerosols by recreational activities on the beach. Although this genus is widespread in most of the Mediterranean coasts, harmful events have been recorded only in some localities and periods. One of those sites has been studied for 3 years in a high frequency monitoring (EBITOX project) in order to elucidate the relationship between the microalgal community and its toxicity., This study was funded by the Spanish national project EBITOX (Study of the biological and toxinologic aspects of benthic dinoflagellates associated with risks to the human health) CTQ2008-06754-C04-04. We are in debt with A. Alastuey (Institut Jaume Almera, CSIC) who let us the aerosol samplers. We also acknowledge the support given by the Water Catalan Agency (Generalitat de Catalunya), I. Manzano (CZ Veterinari, S.A. Porriño, Pontevedra) for providing sheep blood for testing the hemolytic activity, and the facilities kindly offered by the family Aceña from the Restaurant Pins Mar (Sant Andreu de Llavaneres).

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9 pages, 5 figures, 1 table, A recurrent Alexandrium minutum bloom in the Arenys de Mar harbour (Catalan coast, North Western Mediterranean) was monitored in order to establish the relationship between vegetative cells and cyst production. The bloom lasted from January 21 to February 24, 2002 and reached cell concentrations of up to 47 × 106 cell L-1. Two aspects related to the resting cysts deposition were studied: (i) production of resting cysts during the bloom period (by means of sediment traps) and (ii) distribution of resting cysts in the sediment after the bloom (May 2002). Cyst formation in Arenys clearly started in a period with high vegetative cell densities in the water column. Once production was initiated encystment fluxes remained constant for two weeks, and covering the periods of maintenance and decline of the bloom. High cyst fluxes (up to 6000 cysts cm-2 day-1) were quantified as a result of the high vegetative cell concentration. Moreover, encystment occurring in less than 1% of the total population indicates that most of the cells are not involved in resting cysts formation. A comparison of the resting cyst flux values obtained from the sediment traps and the resting cyst concentrations in surface sediment (628-3270 cysts cm-3) three months later, revealed that the number of cysts in the sediment decreased during that time. The studies of excystment showed a high germination percentage (91%) and germling viability (100%). These data, together with the resting cyst distribution in the sediment, are important in assessing the role of resting cysts in the bloom dynamics of A. minutum in confined waters, This study was funded by the EU Project STRATEGY (EVK3-CT-2001–00046)