Historical cyst record as evidence for the recent introduction of the dinoflagellate Gymnodinium catenatum in the north-eastern Atlantic

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 rias (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 Moroccan coast. This study presents results obtained from cyst analyses of a (210)Pb-dated box core and a (14)C-dated piston core, collected off Iberia, covering the last 2 000 years. They indicate that G catenatum is not endemic to the area but has been introduced around the beginning of the last century, coinciding with another major environmental change, possibly related to cultural eutrophication.