The dinoflagellate genus Alexandrium (Halim) in New Zealand coastal waters: comparative morphology, toxicity and molecular genetics

Morphological descriptions, toxicity data and an analysis of LSU rRNA gene sequences are presented for seven species within the marine dinoflagellate genus Alexandrium (Halim), identified in New Zealand coastal waters. All species were established in culture and comparison of their morphology with descriptions from the literature showed these isolates to correspond to the previously described taxa: A. catenella, A. tamarense, A. fraterculus, A. concavum, A. ostenfeldii, A. margalefi and A. pseudogoniaulax. With the exception of A. ostenfeldii, none of these species has previously been recorded in New Zealand. Most of these species are widespread and common, though they are rarely abundant, A. fraterculus has been the most frequent bloom former. Three species, A. catenella, A. tamarense, A. ostenfeldii, produced paralytic shellfish poisoning (PSP) toxins but to date only A. catenella has been associated with a significant shellfish-toxin contamination event. A. catenella and A. tamarense isolates produced toxin profiles predominating in low specific toxicity N-sulfo-carbamoyl analogues, and had identical LSU rRNA gene sequences which place them within the Pacific/Asian clade. The formation of putative hypnozygotes in mating experiments between A. tamarense and some A. catenella isolates suggested these were sexually compatible. However, although>70% of these cysts germinated, the survival of the progeny was poor. A. pseudogoniaulax and A. concavum are the most distantly related to other species within the genus.