Large bloom-forming dinoflagellates can alter aquatic biodiversity and impact human use, posing conservation challenges. We used the maximum entropy (MaxEnt) model to predict the potential distribution of two Ceratium congeners, C. hirundinella and C. furcoides and reviewed known temperature tolerances across their introduced ranges in the American continent. MaxEnt models performed well, predicting 59% global environmental suitability for C. furcoides and 19% for C. hirundinella, with a 22% overlap in suitable areas. Reported co-occurrences in the literature occurred within these predicted overlap areas. Model response curves reflected patterns consistent with the observed water temperature distributions, with C. furcoides associated with higher mean temperatures than C. hirundinella. Future research should integrate bloom event records with quantitative measures of cell density and biomass, as the correspondence between high-suitability areas and reported impacts indicates that such data could enhance risk assessments and support more effective mitigation of the ecological impacts caused by the continuing spread of Ceratium.
