Paralytic shellfish poisoning toxins in France linked to a human-introduced strain of Alexandrium catenella from the western Pacific: evidence from DNAand toxin analysis

In 1998, the toxins responsible for paralytic shellfish poisoning(PSP) were detected in Thau Lagoon, France. The causative organismwas identified as Alexandrium tamarense, a member of the ‘tamarensis’species complex. This dinoflagellate was first observed in thelagoon in 1995 by a monitoring programme following more thana decade with no observations of this species. The species isthus new to these waters, but its origins were unknown. In thispaper, morphological and molecular data are analysed for twoclonal cultures established from the 1998 bloom. These dataare compared to results from Alexandrium isolates originatingelsewhere in the world to infer an origin. Thecal plate morphology,restriction fragment length polymorphism, DNA sequencing andtoxin analyses demonstrate that the Thau Lagoon strains areA. catenella, and are closely related to populations of A. catenellafound in temperate Asia, specifically the Japanese TemperateAsian ribotype of the tamarense/catenella/fundyense speciescomplex. They show no homology with strains from western Europeanwaters, including the Mediterranean. Until now, the JapaneseTemperate Asian ribotype has not been reported outside the westernPacific. The most likely scenario is that A. catenella was introducedto Thau Lagoon via the ballast water of a ship docked at Sète,France, a shipping port in direct communication with the lagoon.This case provides a clear example of the dispersal of a toxicAlexandrium species, probably via human activities.