Protoperidinium bolmonense sp. nov. (Peridiniales, Dinophyceae), a small dinoflagellate from a brackish hypereutrophic lagoon (South of France)

N. Chomérat and A. Couté. 2008. Protoperidinium bolmonense sp. nov. (Peridiniales, Dinophyceae), a small dinoflagellate from a brackish hypereutrophic lagoon (South of France). Phycologia 47: 392–403. DOI: 10.2216/07-82.1 Described is a new Protoperidinium species from a brackish and hypereutrophic lagoon in the South of France, the Bolmon lagoon (‘Étang de Bolmon’). Protoperidinium bolmonense sp. nov. is a small dinoflagellate with a plate formula of Po, X, 4′, 3a, 7″, 3c, 4(?)s, 5‴ and 2″″. Its peculiar features are the presence of only three cingular plates, the marked extension of the second intercalary plate (2a) which abuts the second precingular plate (2″), the marked dorsoventral flattening and the shape of characteristic plates. Different variations of the epithecal plate pattern were observed in P. bolmonense population, involving the division or the fusion of pre-existing plates. Only one other Protoperidinium species, P. vorax, is known to possess only three cingular plates, but the thecal plate arrangement is not exactly the same. The relationship with other congeneric species and the position within the genus are discussed. From an ecological point of view, P. bolmonense was present in spring, in an oligo-mesohaline range of the salinity, which is not usual for Protoperidinium species. Because of the hypereutrophic conditions pertaining in the lagoon, the phytoplankton was abundant with dominant Planktothrix agardhii (cyanoprokaryota) and other autotrophic species. So, the latter might represent an important source of food for some marine heterotrophic dinoflagellates, especially those that can tolerate brackish water. In such environments, where large amounts of phytoplankton species are mixed, the identification of small dinoflagellates can be tedious. Scanning electron microscopy is very useful, and a simple method is described to isolate, prepare and observe a few dinoflagellate cells.