Toxicity of Pseudo-nitzschia populations from Bizerte Lagoon, Tunisia, southwest Mediterranean, and first report of domoic acid production by P. brasiliana

Abstract

Identification of species within the diatom genus Pseudo-nitzschia H. Peragallo, some of which produce the neurotoxin domoic acid (DA), causative agent of amnesic shellfish poisoning (ASP), is crucial for biotoxin monitoring and decision making concerning shellfish harvesting. The occurrence of this genus is reported here at species-complex resolution, for samples collected during one year from March 2006 to February 2007 in Bizerte Lagoon (northern Tunisia) and at one coastal station located in the southwest Mediterranean Sea. Six morphospecies (P. brasiliana Lundholm, Hasle & Fryxell, P. calliantha Lundholm, Moestrup & Hasle, P. delicatissima (Cleve) Heiden complex species, P. pseudodelicatissima (Hasle) Hasle, P. multistriata (Takano) Takano and P. seriata (Cleve) H. Peragallo group species) were observed in the field samples and their periodicity was studied. Five taxa (P. brasiliana, P. cf. delicatissima, P. pseudodelicatissima, P. multistriata and P. cf. seriata) were described for the first time for Bizerte Lagoon. Species of the P. delicatissima complex were the most common, represented in 61% of the samples, followed by P. multistriata, P. calliantha and P. brasiliana, which were found in 20–33% of the samples. The rarest species were P. pseudodelicatissima and species of the P. seriata group, which were present in only 7 and 5% of the samples, respectively. Densest Pseudo-nitzschia blooms (>10⁶cells L⁻¹) were caused by P. delicatissima-complex species (March 2006) and P. brasiliana (October 2006). One P. brasiliana isolate and two strains of P. cf. delicatissima produced DA in culture (8.9 and 7.5–9.5 fg cell⁻¹, respectively). This study gives the first report of DA production in P. brasiliana, based on the retention time of a DA standard and its position relative to an internal standard, using high-performance liquid chromatography (HPLC). Our study calls attention to the probable occurrence of an ASP event in the region, where important shellfish aquaculture sites are located, and therefore the requirement for a more intensive monitoring.

Keywords:

• Pseudo-nitzschia
• ultrastructure
• domoic acid
• Pseudo-nitzschia brasiliana
• toxicity
• Bizerte Lagoon
• aquaculture

Acknowledgements

We gratefully thank Claude Léger (Fisheries and Oceans Canada, Moncton, New Brunswick, Canada) for the DA analyses and James Ehrman (Digital Microscopy Facility, Mount Allison University, Sackville, New Brunswick, Canada) for producing scanning electron micrographs used in this study.