Integrative characterization of Ostreopsis cf. ovata (Dinophyceae) in the central and southwestern Gulf of California: Morphology, molecular phylogeny, and toxicity assessment

Potentially toxic dinoflagellates of the genus Ostreopsis are expanding their distribution globally, with a marked increase in the frequency of Benthic Harmful Algal Blooms (BHABs). Six of the twelve species of Ostreopsis produce a highly potent non-proteinaceous toxin known as palytoxin (PLTX) and its analogs, posing a significant threat to human and environmental health. The study of BHAB species, particularly the genus Ostreopsis, is a recent development in Mexico. With a comprehensive approach, this study aimed to taxonomically and toxicologically characterize Ostreopsis strains from three locations in the central and southeastern Gulf of California. Morphometric and tabular analyses suggested that Ostreopsis cf. ovata and O. fattorussoi are the most probable morphospecies. However, phylogenetic analyses inferred from LSU rDNA (D1-D3) and ITS rDNA sequences further narrowed our results to the Ostreopsis ovata species complex, which also suggests its dominance in the region. In a composite sample (three strains from each of the three locations) chemically analyzed with LC-MS/MS, no intact palytoxins were found; however, amine aldehyde fragment derivatives common to PLTX, OST-D, OVTX, 42-OH PLTX, deoxy PLTX, and isobaric PLTX, were found at low intracellular concentrations. These findings were consistent with an Artemia franciscana bioassay, as the mortality rate after 48 h of exposure was below 10 % and showed no significant differences (p > 0.05) between the control and experimental conditions. Therefore, it is concluded that the tested strains of O. cf. ovata do not currently represent a risk to human or ecosystem health.