Pigment profile and toxin composition during a red tide of Gymnodinium catenatum Graham and Myrionecta rubra (Lohman) Jankowski in coastal waters off Mar del Plata, Argentina

Microscope observations of samples, collected in autumn 2003 during a red tide in the coastal waters of Mar del Plata, Argentina, suggest that the phytoplankton community consisted mainly of the chain-formingdinoflagellate Gymnodinium catenatum (89 000 cells l.1). However, the unusually high concentration of chlorophyll a (171ƒÊg l.1) and the relative abundance of alloxanthin (73%) among the carotenoid pigments measured by high-performance liquid chromatography (HPLC)indicated that cryptophyceans predominated in these samples. Re-examination of Lugolfs preserved plankton samples under high magnification revealed the presence of a low number of recognisable individuals of the ciliate Myrionecta rubra, together with a high abundanceof cytoplasmic contents of their broken cells. Analysis of toxin composition of these samples by HPLC with fluorescence detection showed that, as in most of the G. catenatum strains reported from different geographicalorigins, the toxin profile was dominated (82%) by the less potent N-sulfocarbamoyl toxins. However, the toxin profile of the studied G. catenatum population exhibited certain atypical aspects: it contained the toxins C1,2, GTX4, GTX2,3 and dcGTX2,3, while lacking GTX5, GTX6, C3, C4 and the recently described hydroxybenzoate saxitoxin analogues GC1.3. The toxin profile of this population differed from thosereported for Uruguayan strains, despite their geographic proximity. These results suggest that the observed G. catenatum bloom was a local event, which was not directly related to the transport of an establishedpopulation from the estuarine region of the Rio de la Plata. No harmful effects attributable to this red tide were observed on the Mar del Plata coast