Gymnodinium litoralis sp. nov. (Dinophyceae), a newly identified bloom-forming dinoflagellate from the NW Mediterranean Sea

Recurrent high-biomass blooms of a gymnodinioid species have been periodically 37 recorded at different sites in the NW Mediterranean Sea (Catalan and Sardinian coast), 38 causing intense discolorations of the water. In this study, several strains of the causative 39 organism were isolated and subsequently studied with respect to the morphology of the 40 vegetative cells and different life cycle stages, pigments profile, and molecular 41 phylogeny. Based on phylogenetic analyses, the strains were placed within the 42 Gymnodinium sensu stricto clade. The species possessed a horseshoe-shaped apical 43 groove running anticlockwise around the apex and the major accessory pigment was 44 identified as peridinin. These characteristics place the organism within the 45 Gymnodinium genus, as defined today, although some other characteristics, such as 46 vesicular chambers in the nuclear envelope and a nuclear fibrous connective were not 47 observed. Morphologically, the isolates highly resemble Gyrodinium vorax (Biecheler) 48 but major differences with the latter suggest that they comprise a new species, 49 Gymnodinium litoralis sp. nov. The resting cyst of this species is described herein from 50 field samples of the Catalan and Sardinian coast; pellicle cysts were observed in field 51 samples and also in cultures. This species recurrently produces high biomass blooms (>106 cell L-152 ) in summer along several beaches and coastal lagoons in the NW 53 Mediterranean Sea (L‘Estartit, La Muga River mouth, and Corru S‘Ittiri). Knowledge 54 about its geographic distribution is limited, since the precise identification of G. litoralis 55 from the field or fixed samples can be difficult. Therefore we expect that molecular 56 studies will reveal a much wider distribution of the species.Financial support was provided by the Agència Catalana de l‘Aigua (Department de 573 Medi Ambient, Generalitat de Catalunya) and the CSIC through the contract ‗‗Pla de 574 vigilància de fitoplàncton nociu i tòxic a la Costa Catalana‖. We thank N. Cortadellas 575 from the Unitat de Microscopia Electrònica, Facultat de Medicina-SCT, Universitat de 576 Barcelona and J.M. Fortuño (ICM) for their technical assistance during TEM and SEM 577 analyses, respectively, M. Mas for preparing the latin description and V. Balagué (ICM) 578 for her technical assistance during molecular analyses.Peer reviewe