Morphological and phylogenetic characterization of Amphidinium spp. (Dinophyceae) strains from the Bay of Biscay and the Mediterranean Sea.

Supervisors: Sergio Seoane, Aitor Laza-Martínez (PiE-UPV/EHU).
Members of Amphidinium are among the most abundant and diverse benthic dinoflagellates worldwide, as they range from fresh-water to marine sandy sediments in tropical, sub-tropical, and temperate ecosystems. Some Amphidinium species can still be qualified as cryptic. This issue proves to be of great importance, as diverse reports have demonstrated the potential toxicity of some species, with the dangers it can result from such as fish mortality. The correct identification at species level is therefore critical for a deepen insight into the ecology of the different species, which could help to understand the causes and mechanisms of the toxin production. The current study focuses on the identification of strains isolated from diverse areas from the Bay of Biscay (Spanish Basque Coast; eleven strains) and the Mediterranean Sea (Spanish, Maltese and Slovenian coasts; nine strains). Five morphospecies were identified from the Bay of Biscay. Most of them appeared to belong to the A. operculatum complex (four strains), followed in occurrence by A. carterae (three strains), A. thermaeum (two strains), A. massartii (one strain) and A. steinii (one strain). In the Mediterranean Sea the morphospecies A. carterae (eight strains) and A. operculatum (one strain) were identified. The semicryptic nature of some of the species hampered their morphological identification, highlighting the need of the molecular identification of the strains. For this purpose, we proceeded to the amplification of the D1-D3 region of the 26S Large Sub-Unit ribosomic DNA by PCR, followed by a phylogenetic analysis. Results did not differ for A. operculatum but demonstrated the cryptic nature of A. carterae with other Amphidinium species. Five species were identified from the Bay of Biscay belonging to A. operculatum complex (four strains), A. carterae and A. thermaeum (two strains), A. massartii and A. tomasii (one strain). Four species were identified from the Mediterranean Sea: A. carterae (six strains), A. operculatum, A. thermaeum and A. massartii (one strain). We then gave a first approach for their possible biogeography, from which we concluded their apparent belonging to warm-water, sub-tropical areas. The cause of the occurrence of such warm-water biota within temperate areas was linked to the global rise of sea temperature and the “tropicalization” of the Mediterranean Sea.

Key-Words: Amphidinium, Bay of Biscay, Mediterranean Sea.