Ostreopsis cf. ovata (Dinophyta) bloom in an equatorial island of the Atlantic Ocean

► A bloom of O. cf. ovata is described at the isolated Saint Paul’s Rocks. ► The Archipelago is not inhabited and not subjected to eutrophication. ► Possible causes of the bloom are presented. ► O. cf. ovata blooms in oceanic islands may potentially cause harmful effects to marine animals. The epi-benthic dinoflagellate Ostreopsis cf. ovata Fukuyo has an increasingly global distribution. In Brazil there are reports of O. cf. ovata along the coast from 8°S to 27°S latitude and blooms have been registered on the Rio de Janeiro coastline. In the current study, an O. cf. ovata bloom is reported at Saint Paul’s Rocks (0°55′10″N; 29°20′33″W), between the southern and northern hemispheres. The Archipelago is not inhabited and not subjected to eutrophication, due to isolation, and sustains a number of endemic species. Therefore, blooms of O. cf. ovata may potentially cause demise to trophic chains by affecting marine invertebrates and vertebrates.