Pico- and Nanophytoplankton Dynamics in Two Coupled
but Contrasting Coastal Bays in the NW Mediterranean Sea (France)
Floriane Delpy
1
&
Bruno Serranito
1
&
Jean-Louis Jamet
1,2
&
Gérald Grégori
3
&
Christophe Le Poupon
1,2
&
Dominique Jamet
1,2
Received: 9 October 2017 /Revised: 12 April 2018 /Accepted: 21 April 2018
#
Coastal and Estuarine Research Federation 2018
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.
Keywords Pico- and nanophytoplankton
.
Flow cytometry
.
Coastal environments
.
Mediterranean Sea
.
Spatiotemporal
distribution
Introduction
Picophytoplankton (size = 0.2–2 μm) and nanophytoplankton
(size = 2–20 μm) constitute an important component of aquatic
ecosystems. Pico- and nanophytoplankton contribute up to 43–
50% and 20–32%, respectively, of total primary production
(~0.27 g C m
−2
d
−1
)intheBintermittently blooming waters^
of the Mediterranean Sea (Uitz et al. 2012). Picophytoplankton
are composed of drifting cells, both prokaryotic and eukaryotic
ones. Throughout the world’s oceans, the most abundant auto-
trophic cells are often the smallest ones, such as the
cyanobacteria Prochlorococcus and Synechococcus (< 1 μm
in size), followed by pico- and nanoeukaryotes especially in
coastal eutrophic areas (Partensky et al. 1999; Siokou-Frangou
et al. 2010; Bec et al. 2011). For instance, in the disturbed bay of
Marseille (NW Mediterranean Sea), cyanobacteria, pico- and
nanoeukaryotes have reached maximum abundances of 7 ×
10
4
,3×10
4
and 9 × 10
3
cells mL
−1
(Grégori et al. 2001).
Pico- and nanophytoplankton constitute an integral compart-
ment at the basis of aquatic food webs, contributing to the
microbial loop and, to a lesser extent, to the transfer of energy
and matter towards higher trophic levels (Stockner 1988; Fogg
1995). The increase in biomass of pico- and nanophytoplankton
can significantly contribute to the total particulate organic car-
bon (POC) export fluxes (up to 2–13% for Synechococcus,1–
20% for Prochlorococcus and 6–43% for nanoeukaryotes), es-
pecially according to sudden environmental forcing (Lomas and
Communicated by Hans W. Paerl
* Floriane Delpy
floriane.delpy@univ–tln.fr
* Dominique Jamet
d.jamet@univ–tln.fr
1
Université de Toulon, Laboratoire PROTEE EA 3819, CS 60584,
83041 Toulon, cedex 09, France
2
Université de Toulon, Aix-Marseille Université, CNRS/INSU, IRD,
MIO UM 110, Mediterranean Institute of Oceanography, La
Garde, France
3
Aix-Marseille Université, Université de Toulon, CNRS/INSU, IRD,
MIO UM 110, Mediterranean Institute of Oceanography,
13288 Marseille, France
Estuaries and Coasts
https://doi.org/10.1007/s12237-018-0412-9
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