Diversity and distribution of species of the planktonic diatom genus Pseudo-nitzschia (Bacillariophyceae) from the Gulf of Tehuantepec, southern Mexican Pacific

All species of the diatom genus Pseudo-nitzschia Peragallo are marine and truly planktonic. Many species are widely distributed, and some are recognized to produce domoic acid, a toxin causing amnesic shellfish poisoning (ASP) in humans, therefore it is relevant identifying and monitoring the species of the genus. The purpose of this work was to recognize the species of Pseudo-nitzschia from the Gulf of Tehuantepec, located in the southern Mexican Pacific. Fiftyeight fixed samples collected by net from 4 oceanographic cruises carried out in the Gulf of Tehuantepec, were analysed by light, scanning electron and transmission electron microscopy. Ten morphospecies were identified, described, and illustrated: Pseudo-nitzschia cuspidata, P. delicatisdii and P. subfraudulenta. All species identified conform the basic and detailed morphology (e.g. valves, striae, poroids structure, central interspace) and morphometric data previously given in the literature. Some species are flagged as potentially toxic, although no toxic bloom was documented during the period of samplings. Their local distribution is given, and their world distribution is discussed. Pseudo-nitzschia cuspidata and P. heimii are new documented records in the Mexican Pacific. A list of Pseudo-nitzschia taxa found in the Mexican Pacific is provided.