Phycologia Archimer July 2008, Volume 47, Issue 4, Pages 392–403 Archive Institutionnelle de l’Ifremer http://dx.doi.org/10.2216/PH07-82.1 http://www.ifremer.fr/docelec/ © 2008 International Phycological Society Protoperidinium bolmonense sp. nov. (Peridiniales, Dinophyceae), a small dinoflagellate from a brackish hypereutrophic lagoon (South of ailable on the publisher Web site France) Nicolas Chomérat1, * and Alain Couté2 1 IFREMER, Laboratoire Environnement et Ressources/Finistère Bretagne-Nord 13, rue de Kérose, F-29187 Concarneau Cedex, France 2 Muséum National d'Histoire Naturelle, Département R.D.D.M. – USM 505, 57, Rue Cuvier – Case 39, F-75005 Paris, France blisher-authenticated version is av *: Corresponding author : N. Chomérat, email address : [email protected] Abstract: 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 ccepted for publication following peer review. The definitive pu 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. Keywords: Brackish water, Dinoflagellates, Dinophyceae, Ecology, Coastal lagoon, Mediterranean area, Peridiniales, Phytoplankton, Salinity, Scanning electron microscopy, Taxonomy Please note that this is an author-produced PDF of an article a 1 Introduction Protoperidinium Bergh is a large genus of dinoflagellates (Dinophyceae), usually without chloroplasts and regarded as heterotrophic (Olseng et al., 2002). Because of its extreme diversity, this genus has had a long and complex taxonomic history (Gribble & Anderson, 2006). Most of the species had been formerly described as Peridinium Ehrenberg species, which included marine and freshwater organisms, and, originally, also species now placed in different genera. Bergh (1881) noticed that thecal plates always exhibit a certain basic pattern common within a genus and he introduced the genus Protoperidinium which included species with distinct sulcal lists, but leaving in Peridinium those with antapical horns or without sulcal lists. The importance of the morphology in identifying dinoflagellates was emphasized by Schütt (1895) and the genus Peridinium was divided by several workers into subgroups based on the cell outline and girdle displacement. Kofoid (1909) proposed a detailed description of thecal plates, upon which the current and generally accepted classification is based. Subsequently, Jörgensen (1912), emphasized the importance of thecal plate pattern in identifying species, and proposed new groups. Species with three intercalary plates were maintained in the genus Peridinium, whose subdivisions were based on the shape of the first apical 1′ plate, and the shape and position of the second intercalary 2a plate. The new genus Archaeperidinium was proposed for species with only two anterior intercalary plates. Some workers preferred to consider these genera as two sub-genera of Peridinium but used the subdivisions system of Jörgensen (Lebour, 1925) or adapted it (Paulsen, 1931). However, some investigators noticed that the number and shape of cingular and sulcal plates could be of a great interest in Perididium (sensu lato) taxonomy (cf. Taylor, 1976). Balech (1963) and Loeblich (1968) realized that marine 3 species of Peridinium were all found to possess three cingular plates plus a transitional plate, which contrasted with freshwater species that may have more cingular plates. Bourrelly (1968) investigated the cingular plates of twelve freshwater species and found that there were five or six plates. Balech (1974) transferred 231 marine species of Peridinium to the genus Protoperidinium. It included species with ortho, meta and para apical 1′ plate, intercalary plate with quadra, penta and hexa-type, four cingular plates, and six sulcal plates. Species with ortho-type of 1′ plate, five or six cingular plates and six sulcal plates were retained in Peridinium. Moreover, Balech (1974) found the subgenera useful to distinguish some abnormal plate numbers in the genus Protoperidinium, e.g. two intercalary plates in Archaeperidinium, six precingular in Minusculum and Protoperidinium for species with the typical plate formula Po, X, 4′, 3a, 7′′, 4c, 6(7)s, 5′′′, 2′′′′. Brackish waters are defined as a mixing of fresh water and sea water and exhibit biological communities with peculiar characteristics, which differentiate them from adjacent marine and continental biomes. As brackish waters, and especially coastal lagoons, are an area of colonization of freshwater and marine organisms, species well adapted to the conditions of low salinity and specific to these habitats cohabit with halotolerant species from the adjacent sea and freshwater tributaries (Remane & Schlieper, 1971). Since the separation of Peridinium and Protoperidinium into two distinct genera, the former is now considered as a freshwater or brackish genus while the latter is regarded as a strictly marine and cosmopolitan genus (Sournia, 1986; Steidinger & Tangen, 1996). However, coastal lagoons are generally highly productive systems (Barnes, 1980) and blooms of autotrophic species may be favourable to the presence of heterotrophic marine dinoflagellates (Sarno et al., 1993; Chomérat et al., 4 2004). In such conditions, some euryhaline Protoperidinium species may be present in brackish plankton (Caroppo, 2000). The identification of Protoperidinium and Peridinium species in light microscopy is mainly based upon the observation of the cell size and shape, the presence of horns or spines, the shape of apical plate 1′, intercalary plates, the apical pore complex (APC), ornamentation of thecal plates, the displacement of the cingulum, and the number of cingular and sulcal plates. In plankton from brackish areas, where both of these genera can occur mixed in abundant plankton, a correct identification can be tedious when cells are small, rounded and without a characteristic outline shape and antapical appendages. Hence, the use of scanning electron microscopy (SEM) can greatly help to ensure a correct identification. For better results, this requires an isolation of cells and several dehydration steps prior to the observation (Couté, 2002). Unavoidably, some cells to be identified are lost during the preparation process, which can be detrimental when only a few specimens are available. To minimize losses inherent to the dehydration, we propose here a simple method to prepare a few cells to be observed under SEM, and consequently, particularly adapted for the preparation of rare or ‘precious’ taxa. This paper illustrates the thecal plate morphology of a new Protoperidinium, P. bolmonense, collected in a brackish hypereutrophic lagoon, which is an unusual habitat for a Protoperidinium species. This small dinoflagellate has a plate pattern and morphological features that do not correspond to any previously described within the genus. 5 Material and methods Samples collection. Material was collected from the Bolmon lagoon (43°25′ N, 5°11′ E) which is a brackish (oligo-mesohaline) and hypereutrophic lagoon located in the South of France, near Marseille. It measures about 5 km long, up to 1.5 km wide, and is 0.58 km2 in area. Its depth does not exceed 2.2 m. A further description of this ecosystem and of the ten stations sampled is detailed in Chomérat (2005) and Chomérat et al. (2007). Samples were collected with a sampling bottle just under the water surface to avoid floating detritus and were fixed with buffered formaldehyde for subsequent identification and scanning electron microscopy (SEM). Analyses of environmental parameters were carried out according to Chomérat et al. (2007). Light microscopy. Cells were first isolated from field samples with a micropipette under an inverted microscope, and then observed and dissected with a Zeiss Universal compound microscope (Zeiss, Oberkochen, Germany) equipped with plan-apochromatic objectives, Nomarski differential interference contrast (DIC), a digital camera and a drawing tube. Pictures and drawings were realized with the objectives 40/0.75