| Summary: | Dinoflagellates belonging to the genus <i>Gambierdiscus</i> produce ciguatoxins (CTXs), which are metabolized in fish to more toxic forms and subsequently cause ciguatera fish poisoning (CFP) in humans. Five species of <i>Gambierdiscus</i> have been described from the Canary Islands, where CTXs in fish have been reported since 2004. Here we present new data on the distribution of <i>Gambierdiscus</i> species in the Canary archipelago and specifically from two islands, La Palma and La Gomera, where the genus had not been previously reported. <i>Gambierdiscus</i> spp. concentrations were low, with maxima of 88 and 29 cells·g<sup>−1</sup> wet weight in samples from La Gomera and La Palma, respectively. Molecular analysis (LSUrRNA gene sequences) revealed differences in the species distribution between the two islands: only <i>G. excentricus</i> was detected at La Palma whereas four species, <i>G. australes</i>, <i>G. caribaeus</i>, <i>G. carolinianus</i>, and <i>G. excentricus</i>, were identified from La Gomera. Morphometric analyses of cultured cells of the five Canary Islands species and of field specimens from La Gomera included cell size and a characterization of three thecal arrangement traits: (1) the shape of the 2′ plate, (2) the position of Po in the anterior suture of the 2′ plate, and (3) the length−width relationship of the 2″″ plate. Despite the wide morphological variability within the culture and field samples, the use of two or more variables allowed the discrimination of two species in the La Gomera samples: <i>G.</i> cf. <i>excentricus</i> and <i>G.</i> cf. <i>silvae</i>. A comparison of the molecular data with the morphologically based classification demonstrated important coincidences, such as the dominance of <i>G. excentricus</i>, but also differences in the species composition of <i>Gambierdiscus</i>, as <i>G. caribaeus</i> was detected in the study area only by using molecular methods.
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