Distribution verticale de Dinophysis spp au cours d'un cycle de 48 heures dans le port d'Antifer (Normandie)

Time-related Dinophysis spp vertical profiles have been studyed during a 48 hours cycle in a submerged cylindric tank. A coïncidental Gymnodinium sp. (Scrippsiella trochoidea and Prorocentrum triestinum as companion species) red tide was believed to have strong effect on Dinophysis distribution in the upper layer during the tirst 24 hours cycle of the period of investigation (August 30-31, 1991). Between 24 and 48 hours, the sharp decrease of Dinophysis densities as well as the graduai decline observed in the red tide and in the vertical thermal gradient have resulted in a migration of dominant species : D. sacculus and D. cf. acuminata toward subsuperficiallevels (5 to 7 m.d) with a higher range in cells vertical movements. This behavior is very similar to the ones previously observed, in 1988 at Antifer, with the same experimental device, and in 1985, in Vilaine Bay, without isolation of a water column. The sharp decrease of Dinophysis densities in the tirst hours of the experiment is attributed to an encystment process, following an environmental stress.