The geographical origin of the warm-temperate paralytic shellfish poison producer Gymnodinium catenatum Graham is still under debate. It was first reported in the north-eastern Atlantic in 1976, from the Galician rías(North-West Iberia). Since then, and until 1995, recurrent blooms were recorded, with north-south progression of the affected areas, eventually affecting the whole West and South Atlantic coasts of Iberia and the Moroccancoast. This study presents results obtained from cyst analyses of a 210Pb-dated box core and a 14C-dated piston core, collected off Iberia, covering the last 2 000 years. They indicate that G. catenatum is not endemicto the area but has been introduced around the beginning of the last century, coinciding with another major environmental change, possibly related to cultural eutrophication.