125
exchange with the surface, leading to hypoxia or
anoxia in extreme cases. The variation of nitrate
concentration and salinity during the sampling
period with the strong wind (mistral) event
clearly demonstrates that the Berre lagoon was in
a stratifi ed state in early October. On October 18,
vertical profi les of nutrient concentrations showed
differences between surface and bottom (GIPREB
2011 ). The mistral event has contributed to the
mixing of the water mass and has favored its
reoxygenation.
Due to their capacity to migrate along the
water column (i.e., nycthemeral migration),
fl agellate species including A. sanguinea are
known to proliferate in worldwide stratifi ed
waters (Shipe et al. 2008 ; Du et al. 2011 ). Hence,
they contribute for a great part to the regenerated
production based on nutrient remineralization by
the microbial loop in deeper layers. When
photosynthesis becomes light limited, fl agellates
can swim downward the column water to fi nd
inorganic regenerated form of nitrogen such as
ammonium while nitrates are not consumed.
In October 2011, peaks of phytoplanktonic
biomass due to dinofl agellate proliferation were
correlated to higher nitrate concentrations. When
the chlorophyll a content of the lagoon was the
highest (21.81 µg/dm
3 ), A. sanguinea measured
concentration reached up to 445 cells/cm
3
. A recent
study conducted on nutrient uptakes and regeneration rate in the water column suggests that
pelagic regeneration of ammonium can largely
encompass the demand for primary producers’
development (Gouze et al. 2008 ).
As emphasized by Anderson ( 2009 ), harmful
phytoplanktonic outbreaks are increasing over
the years. The fi rst invoked cause is intensifi cation of industrialization and pollution. But global
warming is also believed to trigger algal blooms
(Moore et al. 2008 ). Increase of surface temperature is indeed coherent with dinofl agellate
proliferation in stratifi ed waters. Moreover,
higher exposure to UV due to the depletion of
ozone is a factor of control of the biosynthesis of
photoprotective MAAs (Litchman et al. 2002 ).
Climate change could thus enhance the development of harmful dinofl agellate species as
well as their deadliness. However, this very study
and particularly the effects of the mistral event
point out their consequence may not be clear
concerning these harmful algal blooms and even
display opposite responses. According to the
Mermex group ( 2011 ), the stratifi cation of water
mass could be balanced by more frequent northern
wind event like mistral in the Mediterranean Sea.
In this study, the occurrence of a mistral event
characterized by a mean speed exceeding 20 m/s
was phased with the disappearance of microand nanophytoplankton cells. However, wind and
storms have been considered as factors of resuspension and dispersal leading to the increase of
harmful algal blooms (Anderson 1989 ; Kremp
2001 ). Resuspension and dispersal of a high concentrated inoculum of resistant cysts could indeed
conduct to massive and sudden proliferation if
environmental conditions favor their germination.
6
Conclusion and Perspective
Algal bloom monitoring is a major preoccupation
as proliferations of harmful species can induce
great economic losses and sanitary issues if they
are not anticipated. The Berre lagoon is a brackish
water pool known to host regular phytoplanktonic
blooms involving harmful and red tides species.
As lagoons represent important sources of socioeconomic incomes, their management constitutes
a major concern for today’s society. Since 2000,
the European Water Framework Directive policy
order regular surveys to state about the eutrophication of these ecosystems, aiming at a coordinate
management that could lead to the rehabilitation
of hundreds of sites, including the Berre lagoon.
This study demonstrates that the deployment
of an autonomous fl ow cytometer in this area
constitutes a complementary method to the
monthly monitoring of the phytoplanktonic community performed for many years now. During
one month, the cytometer has characterized at
high frequency the phytoplanktonic assemblage,
resolving several clusters ranging from pico- to
microphytoplankton. Pictures taken by the
instrument helped to identify the largest ones,
composed of red tide dinofl agellate species.
This strategy combined to hydrological variables
Monitoring of a Potential Harmful Algal Species in the Berre Lagoon by Automated…
exchange with the surface, leading to hypoxia or
anoxia in extreme cases. The variation of nitrate
concentration and salinity during the sampling
period with the strong wind (mistral) event
clearly demonstrates that the Berre lagoon was in
a stratifi ed state in early October. On October 18,
vertical profi les of nutrient concentrations showed
differences between surface and bottom (GIPREB
2011 ). The mistral event has contributed to the
mixing of the water mass and has favored its
reoxygenation.
Due to their capacity to migrate along the
water column (i.e., nycthemeral migration),
fl agellate species including A. sanguinea are
known to proliferate in worldwide stratifi ed
waters (Shipe et al. 2008 ; Du et al. 2011 ). Hence,
they contribute for a great part to the regenerated
production based on nutrient remineralization by
the microbial loop in deeper layers. When
photosynthesis becomes light limited, fl agellates
can swim downward the column water to fi nd
inorganic regenerated form of nitrogen such as
ammonium while nitrates are not consumed.
In October 2011, peaks of phytoplanktonic
biomass due to dinofl agellate proliferation were
correlated to higher nitrate concentrations. When
the chlorophyll a content of the lagoon was the
highest (21.81 µg/dm
3 ), A. sanguinea measured
concentration reached up to 445 cells/cm
3
. A recent
study conducted on nutrient uptakes and regeneration rate in the water column suggests that
pelagic regeneration of ammonium can largely
encompass the demand for primary producers’
development (Gouze et al. 2008 ).
As emphasized by Anderson ( 2009 ), harmful
phytoplanktonic outbreaks are increasing over
the years. The fi rst invoked cause is intensifi cation of industrialization and pollution. But global
warming is also believed to trigger algal blooms
(Moore et al. 2008 ). Increase of surface temperature is indeed coherent with dinofl agellate
proliferation in stratifi ed waters. Moreover,
higher exposure to UV due to the depletion of
ozone is a factor of control of the biosynthesis of
photoprotective MAAs (Litchman et al. 2002 ).
Climate change could thus enhance the development of harmful dinofl agellate species as
well as their deadliness. However, this very study
and particularly the effects of the mistral event
point out their consequence may not be clear
concerning these harmful algal blooms and even
display opposite responses. According to the
Mermex group ( 2011 ), the stratifi cation of water
mass could be balanced by more frequent northern
wind event like mistral in the Mediterranean Sea.
In this study, the occurrence of a mistral event
characterized by a mean speed exceeding 20 m/s
was phased with the disappearance of microand nanophytoplankton cells. However, wind and
storms have been considered as factors of resuspension and dispersal leading to the increase of
harmful algal blooms (Anderson 1989 ; Kremp
2001 ). Resuspension and dispersal of a high concentrated inoculum of resistant cysts could indeed
conduct to massive and sudden proliferation if
environmental conditions favor their germination.
6
Conclusion and Perspective
Algal bloom monitoring is a major preoccupation
as proliferations of harmful species can induce
great economic losses and sanitary issues if they
are not anticipated. The Berre lagoon is a brackish
water pool known to host regular phytoplanktonic
blooms involving harmful and red tides species.
As lagoons represent important sources of socioeconomic incomes, their management constitutes
a major concern for today’s society. Since 2000,
the European Water Framework Directive policy
order regular surveys to state about the eutrophication of these ecosystems, aiming at a coordinate
management that could lead to the rehabilitation
of hundreds of sites, including the Berre lagoon.
This study demonstrates that the deployment
of an autonomous fl ow cytometer in this area
constitutes a complementary method to the
monthly monitoring of the phytoplanktonic community performed for many years now. During
one month, the cytometer has characterized at
high frequency the phytoplanktonic assemblage,
resolving several clusters ranging from pico- to
microphytoplankton. Pictures taken by the
instrument helped to identify the largest ones,
composed of red tide dinofl agellate species.
This strategy combined to hydrological variables
Monitoring of a Potential Harmful Algal Species in the Berre Lagoon by Automated…