Gymnodinium catenatum cell numbers and associated hydrographic structures were studied on the western coast of the Iberian Peninsula during two cruises covering contrasting sesons: autumn and spring. A poleward slope current carrying subtropical oceanic water from the Portuguese coast to the Rías Baixas was observed during both cruises. G. vatenatum was absent in this poleward current, where small naked dinoflagellates were dominant. The downwelling front between oceanic and shelf waters that is associated with the slope current caused an extensive accumulation of G. catenatum in shelf waters. Since the northward transport of G. catenatum populations on the shelf was not observed, the postulated dependence of the G. catenatum PSP episodes in the Rías Baixas on those ocurring some days before (10-15 days) on the west coast of Portugal can not be supported. A new explanation on the time-positional evolution of PSP episodes in the Rías Baixas is proposed. The poleward slope current, wich is generated off the Portuguese coast, progresses northward to the Rías Baixas creating the down welling front and accumulating G. catenatum cells from autochthonous populations in the shelf waters. This accumulation may occur on the Portuguese coast for some days before they are detected in the Rías Baixas

4 pages, 5 figures.-- Harmful algae = Algas nocivas: Proceedings of the VIII International Conference on Harmful Algae, Vigo, Spain, 25-29 June 1997

Support for this work was from CICYT project 84-0068 and from EU MORENA project (MAS2-CT93-65)

Peer reviewed