Abstract

The Pseudo-nitzschia species are a usual component of phytoplankton of the fjords and channels system of southern Chile where producing recurrent blooms, and are considered a toxic or potentially toxic genus in the HABs monitoring program. However, its taxonomic identification has been scarcely developed and it is based in the external morphology to classify the species mainly within the seriata and delicatissima complexes. Here, the identification of the species present in the sub Antarctic ecoregion (45 ° to 56 ° S) of Southern Pacific, is showed. We used a total of 75 samples distributed within the study area obtained between 2006 and 2016. Morphological characterization of the species was performed first with optical microscopy and Nomarski interference contrast (NIC) to observe the contour, end- shape and overlap length of the valves, and extension of the chain. Later the samples were digested to eliminate the organic material. Silica frustules were observed with Scanning Electron Microscopy (SEM), considering the more conspicuous morphological characteristics used for diagnosis at level of Pseudo-nitzschia species. These are: length, width, striae, fibulas (10 μm), poroids (1 μm), presence or absence of central interspace (CIS), row number of poroids and type of hymen pores for the delicatissima complex. Five species were identified: P. australis, P. pungens, P. subpacifica, P. calliantha and P. delicatissima. The results of this study are the first taxonomic identification of the species that make up the genus Pseudo-nitzschia in sub-Antarctic waters of the southern Pacific.