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

In 1998, the toxins responsible for paralytic shellfish poisoning (PSP) were detected in Thau Lagoon, France. The causative organism was identified as Alexandrium tamarense, a member of the 'tamarensis' species complex. This dinoflagellate was first observed in the lagoon in 1995 by a monitoring programme following more than a decade with no observations of this species. The species is thus new to these waters, but its origins were unknown. In this paper, morphological and molecular data are anaysed for two clonal cultures established from the 1998 bloom. These data are compared to results from Alexandrium isolates originating elsewhere in the world to infer an origin. Thecal plate morphology, restriction fragment length polymorphism, DNA sequencing and toxin analyses demonstrate that the Thau Lagoon strains are A. catenella, and are closely related to populations of A. catenella found in temperate Asia, specfically the Japanese Temperate Asian riboype of the tamarense/catenella/fundyense species complex. They show no homology with strains from western European waters, including the Mediterranean. Until now, the Japanese Temperate Asian ribotype has not been reported outside the western Pacific. The most likely scenario is that A. catenella was introduced to Thau Lagoon via the ballast water of a ship docked at Sete, France, a shipping port in direct communication with the lagoon. This case provides a clear example of the dispersal of a toxic Alexandrium species, probably via human activities.