119
events such as natural fl ooding or strong wind
events) (Gouze et al. 2008 ).
Even nowadays, little is known about the phytoplankton dynamics at fi ne scale and about the
variables controlling it. In shallow coastal ecosystems, phytoplankton abundances are infl uenced, at different time scales, by grazing, local
inputs (nutrients), and turbulent mixing, as
described by Cloern ( 1996 ). However, conventional sampling methods are not suitable to
assess their changes induced by sudden sporadic
events such as wind episodes, freshwater discharges, or spates. There is thus a need for
devices able to run automated and highfrequency analysis independently of the weather
conditions and of the presence of a person. Such
instruments would be very valuable to detect
blooms at an early stage and provide a warning
about a potential harmful algal bloom. This obviously requires analyses performed at a taxonomic level.
In this context, we report in this study a highfrequency in situ monitoring of phytoplankton
in the Berre lagoon by means of a Cytosense
automated fl ow cytometer (Cytobuoy b.v.,
Netherlands). This project has been supported
by CNRS EC2CO, FEDER, and the Council of
Provence Alpes Côte d’Azur Region. Abundances
were measured every hour during October 2011
for species ranging from pico- to small microphytoplankton, some of which identifi ed as
harmful such as Akashiwo sanguinea .
2
The Berre Lagoon
The Berre lagoon receives freshwater inputs
from both three natural rivers and from the artifi -
cial channel of a hydroelectric power station
(Electricité de France (EDF)) built on the northeastern shore. The freshwater from the Durance
River is thus derived and discharged in the
lagoon, bringing with it massive amounts of sediments and organic matter. The lagoon also
receives Mediterranean seawater through the
Caronte channel. It is subjected to multiple
natural (frequent wind events, freshwater discharges, and spates) and anthropic forcing
(industries, inhabitations). Due to the proximity
of several small cities and from the Marseille
metropolis (about 800,000 inhabitants), a pressuring instatement of urban, industrial, and agricultural exploitations has emerged all around the
lagoon shore. Since 1966, the main disturbing
infrastructure has been the power plant, using
and discharging freshwater of the Durance River
for electricity supply (by turbines) into the Berre
lagoon, with a drastic impact on salinity (by
important dilution). All these human activities
have generated wastes and inputs that were
drained in the lagoon and enriched it, particularly in nitrogen and phosphorus. In 2011, the
power plant was responsible for 50 % and 15 %
of total nitrogen and phosphorus inputs, respectively. These high inputs combined with the fast
regeneration rates of the microbial community
(Gouze et al. 2008 ) have fueled the phytoplanktonic species, and as a result, the water mass has
become ultimately eutrophic. For many years,
blooms associated with extreme autotrophic biomass (>150 µg Chl a /dm
3
) and colored waters have
been observed until a regulation of the power
plant discharges was imposed to EDF in 1994
and 2005 (Malkassian 2012 ). The salinity gradient between surface and bottom of the lagoon
maintains a quasi-permanent stratifi cation of the
water column (Nérini et al. 2001 ) and prevents
reoxygenation of the deep layer after the oxygen
depletion that follows blooms. Hypoxia or in
extreme case anoxia, light attenuation, and toxin
production during these blooms have perturbed
the entire ecosystem, which remains eutrophic
(Fig. 1 ) and in a “bad” ecological state according
to RSL (Réseau de Suivi Lagunaire) evaluation
criteria (Mayot et al. 2013 ).
3
The Experimental Setup
In order to detect sudden changes in composition
and abundances of the phytoplanktonic community in the Berre lagoon, the Cytosense (Cytobuoy,
Netherlands) fl ow cytometer was placed in a laboratory nearby the “Berre l’Etang” harbor (Fig. 2 ).
Monitoring of a Potential Harmful Algal Species in the Berre Lagoon by Automated…
events such as natural fl ooding or strong wind
events) (Gouze et al. 2008 ).
Even nowadays, little is known about the phytoplankton dynamics at fi ne scale and about the
variables controlling it. In shallow coastal ecosystems, phytoplankton abundances are infl uenced, at different time scales, by grazing, local
inputs (nutrients), and turbulent mixing, as
described by Cloern ( 1996 ). However, conventional sampling methods are not suitable to
assess their changes induced by sudden sporadic
events such as wind episodes, freshwater discharges, or spates. There is thus a need for
devices able to run automated and highfrequency analysis independently of the weather
conditions and of the presence of a person. Such
instruments would be very valuable to detect
blooms at an early stage and provide a warning
about a potential harmful algal bloom. This obviously requires analyses performed at a taxonomic level.
In this context, we report in this study a highfrequency in situ monitoring of phytoplankton
in the Berre lagoon by means of a Cytosense
automated fl ow cytometer (Cytobuoy b.v.,
Netherlands). This project has been supported
by CNRS EC2CO, FEDER, and the Council of
Provence Alpes Côte d’Azur Region. Abundances
were measured every hour during October 2011
for species ranging from pico- to small microphytoplankton, some of which identifi ed as
harmful such as Akashiwo sanguinea .
2
The Berre Lagoon
The Berre lagoon receives freshwater inputs
from both three natural rivers and from the artifi -
cial channel of a hydroelectric power station
(Electricité de France (EDF)) built on the northeastern shore. The freshwater from the Durance
River is thus derived and discharged in the
lagoon, bringing with it massive amounts of sediments and organic matter. The lagoon also
receives Mediterranean seawater through the
Caronte channel. It is subjected to multiple
natural (frequent wind events, freshwater discharges, and spates) and anthropic forcing
(industries, inhabitations). Due to the proximity
of several small cities and from the Marseille
metropolis (about 800,000 inhabitants), a pressuring instatement of urban, industrial, and agricultural exploitations has emerged all around the
lagoon shore. Since 1966, the main disturbing
infrastructure has been the power plant, using
and discharging freshwater of the Durance River
for electricity supply (by turbines) into the Berre
lagoon, with a drastic impact on salinity (by
important dilution). All these human activities
have generated wastes and inputs that were
drained in the lagoon and enriched it, particularly in nitrogen and phosphorus. In 2011, the
power plant was responsible for 50 % and 15 %
of total nitrogen and phosphorus inputs, respectively. These high inputs combined with the fast
regeneration rates of the microbial community
(Gouze et al. 2008 ) have fueled the phytoplanktonic species, and as a result, the water mass has
become ultimately eutrophic. For many years,
blooms associated with extreme autotrophic biomass (>150 µg Chl a /dm
3
) and colored waters have
been observed until a regulation of the power
plant discharges was imposed to EDF in 1994
and 2005 (Malkassian 2012 ). The salinity gradient between surface and bottom of the lagoon
maintains a quasi-permanent stratifi cation of the
water column (Nérini et al. 2001 ) and prevents
reoxygenation of the deep layer after the oxygen
depletion that follows blooms. Hypoxia or in
extreme case anoxia, light attenuation, and toxin
production during these blooms have perturbed
the entire ecosystem, which remains eutrophic
(Fig. 1 ) and in a “bad” ecological state according
to RSL (Réseau de Suivi Lagunaire) evaluation
criteria (Mayot et al. 2013 ).
3
The Experimental Setup
In order to detect sudden changes in composition
and abundances of the phytoplanktonic community in the Berre lagoon, the Cytosense (Cytobuoy,
Netherlands) fl ow cytometer was placed in a laboratory nearby the “Berre l’Etang” harbor (Fig. 2 ).
Monitoring of a Potential Harmful Algal Species in the Berre Lagoon by Automated…