Pico- and nanophytoplankton dynamics in two coupled but contrasting coastal bays in the NW Mediterranean Sea (France) Article - 2018

Floriane Delpy, Bruno Serranito, Jean-Louis Jamet, Gérald Grégori, Christophe Le Poupon, Dominique Jamet

Floriane Delpy, Bruno Serranito, Jean-Louis Jamet, Gérald Grégori, Christophe Le Poupon, Dominique Jamet, « Pico- and nanophytoplankton dynamics in two coupled but contrasting coastal bays in the NW Mediterranean Sea (France)  », Estuaries and Coasts, à paraître, pp. 2039-2055. ISSN 1559-2723

Abstract

Due to its ecological context, the Toulon bay represents a site of scientific interest to study temporal plankton distribution, particularly pico-and nanophytoplankton dynamics. A monthly monitoring was performed during a two-year cycle (October 2013-December 2015) at two coupled sampling sites, referred to as Little and Large bays, which had different morphometric characteristics and human pressures. Flow cytometry analyses highlighted the fact that pico-and nanophytoplankton were more abundant in the eutrophic Little bay. Furthermore, it evidenced two community structures across the Toulon bays : at times, a co-dominance of picoeukaryotes, nanoeukaryotes, Synechococcus 1-like cells and Prochlorococcus-like cells was found, and at other times, a Synechococcus 1-like dominated community existed. The alternation of one structure or the other can be explained by a combined action of temperature regime, nutrient conditions and degree of contamination. This study showed that pico-and nanophytoplankton dynamics were mainly driven by temperature in both sites, as in other temperate Mediterranean regions. Thus, the community was mainly composed of picoeukaryotes and Prochlorococcus-like cells in the winter (< 15 °C), while it was dominated by Synechococcus 1-like cells in the summer (> 20 °C). Additionally, the multiple human stressors in the Little bay seemed to affect the increase in abundance of Synechococcus 1-like cells as they were preferentially observed in the Large bay.

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