In order to investigate the identity, abundance and toxicity of a distinctive Ostreopsis species present in the southern-central coast of Cuba, Ostreopsis field populations were examined during January-September of 2010. The morphological and partial LSU phylogenetic data suggested the presence of O. lenticularis, although a very close species like O. labens could not be discarded. Results indicated the presence of palytoxin-like molecules in a natural extract at concentration of 0.12 pg/cell. Ostreopsis populations were very stable through the course of the study, and a maximum of 7.9 × 10⁴ cells/g of macroalgae fresh weight was recorded on June.