Abstract

Species of the potentially toxic diatom genus Pseudo-nitzschia are common components of the phytoplankton community in the fjords and channel systems of the Magallanes Subantarctic region. Despite Pseudo-nitzschia species forming recurrent harmful algal blooms (HABs) in this region, Chilean monitoring programs have his-torically simply grouped species of this genus into two groups (P. group seriata and P. group delicatissima) ac-cording to basic cell morphology under light microscopy, or as Pseudo-nitzschia spp. Based on ultrastructural features obtained from scanning electron microscopy (SEM), this study revealed more diversity within the genus than previously thought, identifying six Pseudo-nitzschia species in the Magallanes Subantarctic region (48 degrees-56 degrees S) from samples collected during a 11-year period (2006-2017). Most importantly, the study: 1) represent the first report on diversity and distribution of Pseudo-nitzschia species in this Patagonian region; 2) expanded the known distribution of P. australis and P. fraudulenta along the Chilean coast (down to 50 degrees S); 3) confirmed previous records of P. pungens and P. cf. delicatissima; and 4) formally confirm the presence of P. heimii and P. calliantha in subantartic waters.