Inter- and intra-specific variability in morphogenetics and toxin composition of Alexandrium spp. in Irish coastal waters

Alexandrium spp. usually occur in low densities during summer along the south and west coasts of Ireland. Field investigations revealed the presence of morphologically similar strains of A. tamarense, A. tamutum and A. minutum. Several strains were cultured, derived through isolation of resting cysts or vegetative cells. Their identification was confirmed using partial sequencing of the LSU rDNA and their phylogeny was established with this marker. HPLC-FLD analysis showed that no strains of A. tamarense or A. tamutum produced paralytic shellfish poisoning (PSP) toxins. PSP toxins (GTX2 and GTX3) were only detected in strains of A. minutum derived from retentive inlets along the South Coast, the only region where shellfish regularly become contaminated with PSP toxins. All strains of A. minutum isolated from the West Coast were non-toxic. Results indicated that biogeographical studies of the various forms of A. minutum using molecular probes based on LSU rDNA sequences are of limited use. These are thought to be the first records of A. tamutum and of a non-toxic form of A. minutum outside of the Mediterranean Sea.