Biology of toxic algae: A study of species of the genus Chrysochromulina (Prymnesiophyceae) and Alexandrium (Dinophyceae)

Abstract

The role of toxins in algal/protozoan interactions, Alexandrium strains were tested against the dinoflagellates Oblea rotunda&Oxyrrhis marina. Some non-toxic Alexandrium strains caused motility loss&grazer cell lysis indicating that PSP toxins weren t involved. Two clones of the haptophyte, Chrysochromulina polylepis, differing in their toxicity, were used in grazing experiments with O. marina. When O. marina was fed the toxic clone, O. marina food vacuoles contained fewer particles&cells grew slower than those fed the non-toxic clone. Allelochemicals from Alexandrium spp.&C. polylepis may support bloom formation by detrimental effects on grazers. Toxicity analysis of C. polylepis synchronized cultures was conducted using an hemolytic assay. Its toxicity was induced by light&increased during early G1 phase. Spirolide production was studied in A. ostenfeldii batch cultures. Total spirolide concentration per unit culture volume was related to cell concentration. An increase in spirolide cell quota occurred at the beginning of the dark phase. Phylogenetic analysis of the A. tamarense species complex with LSU rDNA sequences found a new non-toxic clade from the Mediterranean. Fossil records of the Peridiniales (~190 Ma), Gonyaulacaceae (~180 Ma)&Ceratiaceae (145 Ma) calibrated a molecular clock. Average age of Alexandrium is 77 Ma (Late Cretaceous&Early Paleogene) with earliest possible age at Mid Cretaceous (119 Ma). A. tamarense species complex likely diverged at Early Neogene (23 Ma)&late Paleogene (45 Ma). Hypotheses were proposed to explain the historical biogeography of the species. Amplified Fragment Length Polymorphism (AFLP) was established for species genetic diversity studies and used to investigate the genetic diversity within a distinct geographic region or a bloom. SSU&LSU rRNA sequences of Alexandrium ssp. were used to develop probes for the species complex, geographic clades&for A. ostenfeldii to identify them in field samples by FISH.