title: Assessing ultraphytoplankton and heterotrophic prokaryote composition by flow cytometry in a Mediterranean lagoon.
abstract: In the eutrophic Ghar El Melh Lagoon (GML, Tunisia), the distribution of heterotrophic prokaryotes, pico- and nanophytoplankton was studied at five stations in November 2012 at the single cell level, along with environmental factors. Flow cytometry analysis of ultraplankton (<10 μm) resolved (i) two heterotrophic prokaryote groups, low and high nucleic acid contents (LNA and HNA, respectively), and (ii) eight to nine ultraphytoplankton groups (cryptophyte-like cells, two nanoeukaryote subgroups, two picoeukaryote subgroups and three Synechococcus-like cells subgroups). Prochlorococcus was not detected. According to redundancy analysis (RDA), a significant difference was found in the distribution of the ultraplankton between stations (F = 2.61, p < 0.05); maximum proliferations of heterotrophic prokaryotes were observed in the inner parts of the lagoon at stations 3, 4 and 5 affected by urban, agricultural and industrial discharges. Ultraphytoplankton concentrations were the highest near the outlet of the lagoon at stations 1 and 2 influenced by freshwater outflow and oligotrophic Mediterranean water inflow, respectively. At station 1, the large ultraphytoplankton concentration derives from the high abundance of cryptophyte-like cells favoured by the freshwater outflow whereas at station 2, the input of oligotrophic Mediterranean water enhanced the abundance of Synechococcus and picoeukaryotes at the expense of nanoeukaryotes. Two trophic regimes were thus differentiated in GML.
authors.affiliation: Laboratoire de Chrono-Environnement, UMR CNRS 6249, Université de Franche-Comté, Besancon, France.|Laboratoire Milieu Marin, Institut National des Sciences et Technologies de la Mer (INSTM), Centre la Goulette, la Goulette, Tunisia.
authors.forename: Amel
authors.initials: A
authors.lastname: Dhib
authors.affiliation: Institut Méditerranéen d'Océanologie (MIO), Aix Marseille Université, Université de Toulon, CNRS/INSU, IRD, Marseille, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Denis
authors.affiliation: Laboratoire de Chrono-Environnement, UMR CNRS 6249, Université de Franche-Comté, Besancon, France.|Laboratoire Milieu Marin, Institut National des Sciences et Technologies de la Mer (INSTM), Centre la Goulette, la Goulette, Tunisia.
authors.forename: Boutheina
authors.initials: B
authors.lastname: Ziadi
authors.affiliation: Institut Méditerranéen d'Océanologie (MIO), Aix Marseille Université, Université de Toulon, CNRS/INSU, IRD, Marseille, France.
authors.forename: Aude
authors.initials: A
authors.lastname: Barani
authors.affiliation: Laboratoire Milieu Marin, Institut National des Sciences et Technologies de la Mer (INSTM), Centre la Goulette, la Goulette, Tunisia.
authors.forename: Souad
authors.initials: S
authors.lastname: Turki
authors.affiliation: Laboratoire de Chrono-Environnement, UMR CNRS 6249, Université de Franche-Comté, Besancon, France. lotfi.aleya@univ-fcomte.fr.
authors.forename: Lotfi
authors.initials: L
authors.lastname: Aleya
mesh_terms: D005434:Flow Cytometry; D052836:Heterotrophic Processes; D012621:Seasons; D012623:Seawater; D014416:Tunisia
keywords: Eutrophication; Flow cytometry; Heterotrophic prokaryotes; Mediterranean lagoon; Pico- and nanophytoplankton