Diatoms have high productivity and are highly influenced by turbulent conditions. We consider her... more Diatoms have high productivity and are highly influenced by turbulent conditions. We consider here diatoms of the species Pseudo-nitzschia, which are chain forming. The objective of this work was to show how the turbulent environment affects the growth and the chain forming of these species. For this, cultures of the species Pseudo-nitzschia multiseries and Pseudo-nitzschia fraudulenta were performed in the laboratory and submitted to stationary turbulent conditions, using the Agiturb system developed in the LOG at Wimereux (Le Quiniou et al. 2022). In the Agiturb system, the turbulent flow is produced using four contra-rotating agitators that are placed under a cubic tank, generating a statistically stationary, spatially inhomogeneous flow with compression and stretching. The injection of the energy in the flow is produced by 4 stirring bars activated by 4 magnetic stirrers situated at symmetric positions. The cubic tank is almost half-full with 15 liters of sea water. For each experiment, the magnitude of the rotation rate of each agitator was identical, with two agitators rotating clockwise and two anti-clockwise, the same directions being along the diagonal. Different values of the rotation rate were chosen to reach different turbulence levels, characterized by the microscale Reynolds number Rλ going from 130 to 360. These Reynolds numbers correspond to typical values found in the ocean, from the epicontinental zone, to coastal, surf zones and even storm conditions. In the experiments, all the other parameters that affect the diatoms’ proliferation were kept the same. Formation and growth of the chains were assessed through microscopy. P. fraudulenta displayed higher growth than P. multiseries in all turbulence levels except from the control condition (Rλ=0) where the growth was approximately the same. The level of turbulence that was more beneficial for the growth of P. multiseries was the agitated (Rλ= 240) whereas for P. fraudulenta it was for a smaller Reynolds number (Rλ = 160). The chain length were also considered in relation with turbulence level, by considering the probability density of single chains, small chains (2 or 3 cells) and long chains (more than 4 cells). The result was that the predominant form of the cells for both species was the single cells. However, P. multiseries presented higher variations in chain forming throughout the whole experiment than P. fraudulenta. Within this approach, the optimal turbulence level, for growth as well as chain formation, can be assessed for each phytoplankton species.
This study presents the results of the first field application of a flow-through multi-wavelength... more This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593 nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (F v /F m) and functional absorption cross section (σ PSII) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of F v /F m and σ PSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in F v /F m and σ PSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σ PSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II (PSII) pigments. This was particularly true in summer when high σ PSII (593) values were observed later and longer than high σ PSII (458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, F v /F m variations were similar after excitation at 458 nm or 593 nm suggesting that the adjustment of F v /F m in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community.
From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish a... more From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish and mesozooplankton have been reported in the Bay of Biscay. Since significant relationships have been found between phytoplankton chlorophyll a and mesozooplankton as well as between phytoplankton chlorophyll a and shifts in sardine body condition, it was hypothesized that phytoplankton communities may have also been affected during this period and may have played a role in these changes. However, the available data were insufficient to validate this hypothesis and the causes of these changes remained unexplained. The present study analyzed a spatio-temporal marine microphytoplankton dataset collected during the annual PELGAS (PELagiques GAScogne) surveys from 2003 to 2014. The thorough analysis of microphytoplankton taxonomic composition, with an approach integrating the relative role of environmental conditions as well as biotic interactions and applying the concept of ecological niche, confirmed that significant modifications in microphytoplankton community structure occurred during this period. Temporal changes were stronger than spatial differences at these sampling scales. Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. Twenty eight taxonomic units were involved in these community changes. Among them, five were identified as the protagonists (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.). Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure. This study stresses the need to improve our knowledge of phytoplankton species ecological niches and to take into account biotic interactions for a thorough understanding of the processes shaping plankton communities and the resulting diversity patterns. Highlights ► Spring microphytoplankton community structure and diversity were studied over a decade in the Bay of Biscay. ► Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. ► Five main species were responsible for these changes (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.) ► Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure.
temporal variability of phytoplankton (Chlorophyll-a) in relation to salinity, suspended sediment... more temporal variability of phytoplankton (Chlorophyll-a) in relation to salinity, suspended sediment concentration, and light intensity in a macrotidal estuary,
Diatoms have high productivity and are highly influenced by turbulent conditions. We consider her... more Diatoms have high productivity and are highly influenced by turbulent conditions. We consider here diatoms of the species Pseudo-nitzschia, which are chain forming. The objective of this work was to show how the turbulent environment affects the growth and the chain forming of these species. For this, cultures of the species Pseudo-nitzschia multiseries and Pseudo-nitzschia fraudulenta were performed in the laboratory and submitted to stationary turbulent conditions, using the Agiturb system developed in the LOG at Wimereux (Le Quiniou et al. 2022). In the Agiturb system, the turbulent flow is produced using four contra-rotating agitators that are placed under a cubic tank, generating a statistically stationary, spatially inhomogeneous flow with compression and stretching. The injection of the energy in the flow is produced by 4 stirring bars activated by 4 magnetic stirrers situated at symmetric positions. The cubic tank is almost half-full with 15 liters of sea water. For each ex...
This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Tech... more This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Technology and Methodology, Task 3.1 Automated platform for the observation of phytoplankton diversity in relation to ecosystem services. The aim is to provide an advanced report on the last developments dedicated to the observation of the phytoplankton diversity by applying novel techniques on automated platforms. The work was carried out in close connection with task 4.1 Biodiversity of plankton, harmful algal blooms and eutrophication. The partners involved in these developments are CNRS, SYKE, SMHI, HZG, RWS, VLIZ CEFAS and Ifremer. Subcontractors in WP4, task 4.1 are WHOI, Scanfjord AB, Tomas Rutten b.v., CytoBuoy b.v. and UGent - PAE. The work was carried out mainly in the field with activities in the Baltic Sea, the Kattegat-Skagerrak, the Celtic seas-English Channel-North Sea Area, the Western Mediterranean, as well as in shared studies with other WP3.4 and WP4.4 in the Bay of Biscay...
This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Tech... more This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Technology and Methodology,Task 3.1 Automated platform for the observation of phytoplankton diversity in relation to ecosystem services. The aim is to provide an advanced report on the last developments dedicated to the observation of the phytoplankton diversity by applying novel techniques on automated platforms. The work was carried out in close connection with task 4.1 Biodiversity of plankton, harmful algal blooms and eutrophication.The partners involved in these developments are CNRS, SYKE, SMHI, HZG, RWS, VLIZ CEFAS and Ifremer. Subcontractors in WP4, task 4.1 are WHOI, Scanfjord AB, Tomas Rutten b.v., CytoBuoy b.v. and UGent -PAE.The work was carried out mainly in the field with activities in the Baltic Sea, the Kattegat-Skagerrak, the Celtic seas-English Channel-North Sea Area, the Western Mediterranean, as well as in shared studies with other WP3.4 and WP4.4 in the Bay of Biscay and...
From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish a... more From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish and mesozooplankton have been reported in the Bay of Biscay. Since significant relationships have been found between phytoplankton chlorophyll a and mesozooplankton as well as between phytoplankton chlorophyll a and shifts in sardine body condition, it was hypothesized that phytoplankton communities may have also been affected during this period and may have played a role in these changes. However, the available data were insufficient to validate this hypothesis and the causes of these changes remained unexplained. The present study analyzed a spatio-temporal marine microphytoplankton dataset collected during the annual PELGAS (PELagiques GAScogne) surveys from 2003 to 2014. The thorough analysis of microphytoplankton taxonomic composition, with an approach integrating the relative role of environmental conditions as well as biotic interactions and applying the concept of ecological niche, confirmed that significant modifications in microphytoplankton community structure occurred during this period. Temporal changes were stronger than spatial differences at these sampling scales. Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. Twenty eight taxonomic units were involved in these community changes. Among them, five were identified as the protagonists (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.). Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure. This study stresses the need to improve our knowledge of phytoplankton species ecological niches and to take into account biotic interactions for a thorough understanding of the processes shaping plankton communities and the resulting diversity patterns. Highlights ► Spring microphytoplankton community structure and diversity were studied over a decade in the Bay of Biscay. ► Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. ► Five main species were responsible for these changes (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.) ► Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure.
This study presents the results of the first field application of a flow-through multi-wavelength... more This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593 nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (F v /F m) and functional absorption cross section (σ PSII) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of F v /F m and σ PSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in F v /F m and σ PSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σ PSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II (PSII) pigments. This was particularly true in summer when high σ PSII (593) values were observed later and longer than high σ PSII (458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, F v /F m variations were similar after excitation at 458 nm or 593 nm suggesting that the adjustment of F v /F m in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community.
This study is the first in situ work comparing rapid light curves (RLC) and non-sequential steady... more This study is the first in situ work comparing rapid light curves (RLC) and non-sequential steady-state light curves (N-SSLC) in their efficiency to characterize phytoplankton photosynthetic activity and acclimation status. Measurements were carried out at two time scales (daily and annual) using the Pulse Amplitude Modulated fluorometry on samples taken in the coastal waters of a macrotidal ecosystem (the Strait of Dover, eastern English Channel). RLC and N-SSLC were compared under a wide range of environmental conditions and phytoplankton composition in order to define the best methodology to accurately capture short and long-term adjustments in the functioning of the photosynthetic apparatus. The relationships between the photosynthetic parameters extracted from RLC and N-SSLC were also studied to evaluate the possibility to use RLC to predict N-SSLC photosynthetic parameters and thus obtaining the acclimation status at steady state. At daily scale, the maximum electron transport rate and light saturation coefficient resulting from RLC (respectively, ETRm_RLC and Ek_RLC) were found to follow more closely short-term environmental light variations than ETRm and Ek resulting from N-SSLC (ETRm_N-SSLC and Ek_N-SSLC) did. RLC were thus able to detect rapid changes in photosynthetic activity that would have been overlooked with N-SSLC measurements. At annual scale, few differences were found between RLC and N-SSLC. Variations of ETRm and α derived from RLC and N-SSLC were very similar but absolute values were lower for RLC measurements. Because, at daily scale, RLC better capture the short-term changes in photosynthetic activity than N-SSLC do, using RLC to predict N-SSLC photosynthetic parameters and getting information about steady-state acclimation status is not possible at this time scale. However, this can be done at seasonal scale.
ABSTRACT L'utilisation des rapid light curves (RLC) et des steady state light curves (SSL... more ABSTRACT L'utilisation des rapid light curves (RLC) et des steady state light curves (SSLC), pour la caractérisation in situ de l'activité photosynthétique du phytoplancton, à différentes échelles de temps, a été comparée. La possibilité d'utiliser les paramètres photosynthétiques des RLC pour prédire ceux de SSLC a été évaluée. Les résultats montrent que les RLC sont un bon outil pour la caractérisation de l'activité photosynthétique à différentes échelles temporelles
Short-term changes in phytoplankton photosynthetic activity were studied during different periods... more Short-term changes in phytoplankton photosynthetic activity were studied during different periods of the years 2009 and 2010 in the coastal waters of a macrotidal ecosystem (the Strait of Dover, eastern English Channel). During each sampling period, samples were taken every 1.45 h., from sunrise to sunset, during at least 5 days distributed along a complete spring-neap tide cycle. The photosynthetic parameters were obtained by measuring rapid light curves using pulse amplitude modulated fluorometry and were related to environmental conditions and phytoplankton taxonomic composition. The maximum quantum yield (F v /F m) showed clear light-dependent changes and could vary from physiological maxima (0.68-0.60) to values close to 0.30 during the course of 1 day, suggesting the operation of photoprotective mechanisms. The maximum electron transport rate (ETR m) and maximal light utilization efficiency (a) were generally positively correlated and showed large diel variability. These parameters fluctuated significantly from hour to hour within each day and the intraday pattern of variation changed significantly among days of each sampling period. Stepwise multiple linear regressions analyses indicated that light fluctuations explained a part of this variability but a great part of variability stayed unexplained. F v /F m , ETR m and a were not only dependent on the light conditions of the sampling day but also on those of the previous days. A time lag of 3 days in the effect of light on ETR m and a variation was highlighted. At these time scales, changes in phytoplankton community structure seemed to have a low importance in the variability in photosynthetic parameters. The photoacclimation index E k showed a lower variability and was generally different from the incident irradiance, indicating a limited acclimation capacity with a poor optimization of light harvesting during the day. However, in well-mixed systems such as the Strait of Dover, the short-term photoacclimation is disrupted by the high level of variability in environmental conditions. Also, the variability observed in the present study can be associated with a particular kind of photosynthetic response: the ''E k-independent'' variability. The physiological basis of this photosynthetic response is largely unresolved and further researches on this subject are still required to better explain the dynamics of phytoplankton activity in the Strait of Dover.
In this study, we examined the possibility of using the FluoroProbe for monitoring the dynamics o... more In this study, we examined the possibility of using the FluoroProbe for monitoring the dynamics of the Haptophyte Phaeocystis globosa in the coastal waters of the eastern English Channel. The FluoroProbe was recalibrated by recording a new fingerprint for P. globosa and the use of this new fingerprint was tested through a series of laboratory and in situ experiments. The annual dynamics of P. globosa estimated using the FluoroProbe and by flow cytometry were similar. A strong relationship was found between the FluoroProbe estimates of P. globosa biomass expressed in terms of chlorophyll a equivalent per litre (eq. mg L 21) and flow cytometric cell counts (r ¼ 0.889, P , 0.001, n ¼ 121). The FluoroProbe can be used to detect the flagellated cells as well as the colonial cells of P. globosa but not to distinguish these two cell types in mixed assemblages. The use of the new fingerprint recorded for P. globosa improved the detection of Isochrysis sp. This suggests the possibility of using the FluoroProbe to monitor Haptophytes other than P. globosa by calibrating the device with species representative of the region of interest. However, it is important to note that the detection of P. globosa at the species level was possible in the eastern English Channel because it was the only Haptophyte species present with a biomass sufficient to be detected by the FluoroProbe. In areas where several Haptophyte species are simultaneously present, their discrimination will be impossible and in such situations the FluoroProbe can be used to monitor the dynamics of the combined Haptophyte group.
The temporal variability in phytoplankton photosynthetic activity was studied in the coastal wate... more The temporal variability in phytoplankton photosynthetic activity was studied in the coastal waters of the Strait of Dover and related to environmental conditions. Phytoplankton photosynthetic activity data collected from October 2008 and August 2010 at different time scales (hourly to interannual) using a nested sampling design are presented. Photosynthetic parameters including the maximum quantum yield (F v /F m), maximal light utilization efficiency (α), maximum electron transport rate (ETR m) and light saturation coefficient (E k) were measured using Pulse Amplitude Modulation (PAM) fluorometry. Information on the taxonomic composition of phytoplankton assemblages and physicochemical parameters were also collected. Marked changes in photosynthetic parameters were observed at the different time scales investigated. The variability of photosynthetic parameters at sub-seasonal scale (hourly to monthly) could be of the same order of magnitude as at seasonal scale. At short time scale (hour to week), there was no consistent pattern of diel periodicity in photosynthetic parameters. There was a decline of ETR m and α during the day as often as there was a peak at the maximum of irradiance. Light conditions were the main influencing factor on photosynthetic parameters at these time scales. The optimal use of incident irradiance seemed focused on between-days rather than within-day variability. At longer time scale (seasonal to interannual), close interplays between shifts in community taxonomic composition and changes in the physicochemical characteristics of the environment controlled the variability in photosynthetic parameters. Whatever the time scale and period of year considered, variability in photosynthetic parameters was "E k-independent". In well-mixed macrotidal ecosystems, such as the Strait of Dover, a nested sampling design allowing to characterize the short-(intraday and daily) as well as long-term variability (within months, monthly, seasonal, annual and interannual) in photosynthetic parameters is required to get a suitable picture of phytoplankton photosynthesis and avoid potential problems of aliasing.
Diatoms have high productivity and are highly influenced by turbulent conditions. We consider her... more Diatoms have high productivity and are highly influenced by turbulent conditions. We consider here diatoms of the species Pseudo-nitzschia, which are chain forming. The objective of this work was to show how the turbulent environment affects the growth and the chain forming of these species. For this, cultures of the species Pseudo-nitzschia multiseries and Pseudo-nitzschia fraudulenta were performed in the laboratory and submitted to stationary turbulent conditions, using the Agiturb system developed in the LOG at Wimereux (Le Quiniou et al. 2022). In the Agiturb system, the turbulent flow is produced using four contra-rotating agitators that are placed under a cubic tank, generating a statistically stationary, spatially inhomogeneous flow with compression and stretching. The injection of the energy in the flow is produced by 4 stirring bars activated by 4 magnetic stirrers situated at symmetric positions. The cubic tank is almost half-full with 15 liters of sea water. For each experiment, the magnitude of the rotation rate of each agitator was identical, with two agitators rotating clockwise and two anti-clockwise, the same directions being along the diagonal. Different values of the rotation rate were chosen to reach different turbulence levels, characterized by the microscale Reynolds number Rλ going from 130 to 360. These Reynolds numbers correspond to typical values found in the ocean, from the epicontinental zone, to coastal, surf zones and even storm conditions. In the experiments, all the other parameters that affect the diatoms’ proliferation were kept the same. Formation and growth of the chains were assessed through microscopy. P. fraudulenta displayed higher growth than P. multiseries in all turbulence levels except from the control condition (Rλ=0) where the growth was approximately the same. The level of turbulence that was more beneficial for the growth of P. multiseries was the agitated (Rλ= 240) whereas for P. fraudulenta it was for a smaller Reynolds number (Rλ = 160). The chain length were also considered in relation with turbulence level, by considering the probability density of single chains, small chains (2 or 3 cells) and long chains (more than 4 cells). The result was that the predominant form of the cells for both species was the single cells. However, P. multiseries presented higher variations in chain forming throughout the whole experiment than P. fraudulenta. Within this approach, the optimal turbulence level, for growth as well as chain formation, can be assessed for each phytoplankton species.
This study presents the results of the first field application of a flow-through multi-wavelength... more This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593 nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (F v /F m) and functional absorption cross section (σ PSII) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of F v /F m and σ PSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in F v /F m and σ PSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σ PSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II (PSII) pigments. This was particularly true in summer when high σ PSII (593) values were observed later and longer than high σ PSII (458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, F v /F m variations were similar after excitation at 458 nm or 593 nm suggesting that the adjustment of F v /F m in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community.
From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish a... more From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish and mesozooplankton have been reported in the Bay of Biscay. Since significant relationships have been found between phytoplankton chlorophyll a and mesozooplankton as well as between phytoplankton chlorophyll a and shifts in sardine body condition, it was hypothesized that phytoplankton communities may have also been affected during this period and may have played a role in these changes. However, the available data were insufficient to validate this hypothesis and the causes of these changes remained unexplained. The present study analyzed a spatio-temporal marine microphytoplankton dataset collected during the annual PELGAS (PELagiques GAScogne) surveys from 2003 to 2014. The thorough analysis of microphytoplankton taxonomic composition, with an approach integrating the relative role of environmental conditions as well as biotic interactions and applying the concept of ecological niche, confirmed that significant modifications in microphytoplankton community structure occurred during this period. Temporal changes were stronger than spatial differences at these sampling scales. Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. Twenty eight taxonomic units were involved in these community changes. Among them, five were identified as the protagonists (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.). Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure. This study stresses the need to improve our knowledge of phytoplankton species ecological niches and to take into account biotic interactions for a thorough understanding of the processes shaping plankton communities and the resulting diversity patterns. Highlights ► Spring microphytoplankton community structure and diversity were studied over a decade in the Bay of Biscay. ► Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. ► Five main species were responsible for these changes (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.) ► Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure.
temporal variability of phytoplankton (Chlorophyll-a) in relation to salinity, suspended sediment... more temporal variability of phytoplankton (Chlorophyll-a) in relation to salinity, suspended sediment concentration, and light intensity in a macrotidal estuary,
Diatoms have high productivity and are highly influenced by turbulent conditions. We consider her... more Diatoms have high productivity and are highly influenced by turbulent conditions. We consider here diatoms of the species Pseudo-nitzschia, which are chain forming. The objective of this work was to show how the turbulent environment affects the growth and the chain forming of these species. For this, cultures of the species Pseudo-nitzschia multiseries and Pseudo-nitzschia fraudulenta were performed in the laboratory and submitted to stationary turbulent conditions, using the Agiturb system developed in the LOG at Wimereux (Le Quiniou et al. 2022). In the Agiturb system, the turbulent flow is produced using four contra-rotating agitators that are placed under a cubic tank, generating a statistically stationary, spatially inhomogeneous flow with compression and stretching. The injection of the energy in the flow is produced by 4 stirring bars activated by 4 magnetic stirrers situated at symmetric positions. The cubic tank is almost half-full with 15 liters of sea water. For each ex...
This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Tech... more This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Technology and Methodology, Task 3.1 Automated platform for the observation of phytoplankton diversity in relation to ecosystem services. The aim is to provide an advanced report on the last developments dedicated to the observation of the phytoplankton diversity by applying novel techniques on automated platforms. The work was carried out in close connection with task 4.1 Biodiversity of plankton, harmful algal blooms and eutrophication. The partners involved in these developments are CNRS, SYKE, SMHI, HZG, RWS, VLIZ CEFAS and Ifremer. Subcontractors in WP4, task 4.1 are WHOI, Scanfjord AB, Tomas Rutten b.v., CytoBuoy b.v. and UGent - PAE. The work was carried out mainly in the field with activities in the Baltic Sea, the Kattegat-Skagerrak, the Celtic seas-English Channel-North Sea Area, the Western Mediterranean, as well as in shared studies with other WP3.4 and WP4.4 in the Bay of Biscay...
This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Tech... more This is a summary of the activities and results of JERICO-NEXT Work Package 3 Innovations in Technology and Methodology,Task 3.1 Automated platform for the observation of phytoplankton diversity in relation to ecosystem services. The aim is to provide an advanced report on the last developments dedicated to the observation of the phytoplankton diversity by applying novel techniques on automated platforms. The work was carried out in close connection with task 4.1 Biodiversity of plankton, harmful algal blooms and eutrophication.The partners involved in these developments are CNRS, SYKE, SMHI, HZG, RWS, VLIZ CEFAS and Ifremer. Subcontractors in WP4, task 4.1 are WHOI, Scanfjord AB, Tomas Rutten b.v., CytoBuoy b.v. and UGent -PAE.The work was carried out mainly in the field with activities in the Baltic Sea, the Kattegat-Skagerrak, the Celtic seas-English Channel-North Sea Area, the Western Mediterranean, as well as in shared studies with other WP3.4 and WP4.4 in the Bay of Biscay and...
From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish a... more From 2000 to 2016, substantial changes in biomass and community structure of small pelagic fish and mesozooplankton have been reported in the Bay of Biscay. Since significant relationships have been found between phytoplankton chlorophyll a and mesozooplankton as well as between phytoplankton chlorophyll a and shifts in sardine body condition, it was hypothesized that phytoplankton communities may have also been affected during this period and may have played a role in these changes. However, the available data were insufficient to validate this hypothesis and the causes of these changes remained unexplained. The present study analyzed a spatio-temporal marine microphytoplankton dataset collected during the annual PELGAS (PELagiques GAScogne) surveys from 2003 to 2014. The thorough analysis of microphytoplankton taxonomic composition, with an approach integrating the relative role of environmental conditions as well as biotic interactions and applying the concept of ecological niche, confirmed that significant modifications in microphytoplankton community structure occurred during this period. Temporal changes were stronger than spatial differences at these sampling scales. Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. Twenty eight taxonomic units were involved in these community changes. Among them, five were identified as the protagonists (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.). Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure. This study stresses the need to improve our knowledge of phytoplankton species ecological niches and to take into account biotic interactions for a thorough understanding of the processes shaping plankton communities and the resulting diversity patterns. Highlights ► Spring microphytoplankton community structure and diversity were studied over a decade in the Bay of Biscay. ► Three main periods, 2003-2005, 2006 and 2007-2014, showing different community structure, diversity and dominant taxonomic units were highlighted. ► Five main species were responsible for these changes (Pseudo-nitzschia spp., Gymnodinium spp. + Gyrodinium spp., Leptocylindrus danicus, Leptocylindrus minimus and Chaetoceros sp.) ► Variations in water temperature and equivalent freshwater depth constrained the realized ecological niches of these species and explained, at least in part, changes in community structure.
This study presents the results of the first field application of a flow-through multi-wavelength... more This study presents the results of the first field application of a flow-through multi-wavelength Fast Repetition Rate fluorometer (FRRF) equipped with two excitation channels (458 and 593 nm). This device aims to improve the measurement of mixed cyanobacteria and algae community's photosynthetic parameters and was designed to be easily incorporated into existing ferrybox systems. We present a spatiotemporal analysis of the maximum photochemical efficiency (F v /F m) and functional absorption cross section (σ PSII) recorded from April to August 2014 on a ship-of-opportunity commuting twice per week between Helsinki (Finland) and Travemünde (Germany). Temporal variations of F v /F m and σ PSII differed between areas of the Baltic Sea. However, even though the Baltic Sea is characterized by several physico-chemical gradients, no gradient was observed in F v /F m and σ PSII spatial distribution suggesting complex interactions between biotic and abiotic controls. σ PSII was sensitive to phytoplankton seasonal succession and thus differed according to the wavelength used to excite photosystems II (PSII) pigments. This was particularly true in summer when high σ PSII (593) values were observed later and longer than high σ PSII (458) values, reflecting the role of cyanobacteria in photosynthetic light uptake measured at community scale. In contrast, F v /F m variations were similar after excitation at 458 nm or 593 nm suggesting that the adjustment of F v /F m in response to environmental factors was similar for the different groups (algae vs. cyanobacteria) present within the phytoplankton community.
This study is the first in situ work comparing rapid light curves (RLC) and non-sequential steady... more This study is the first in situ work comparing rapid light curves (RLC) and non-sequential steady-state light curves (N-SSLC) in their efficiency to characterize phytoplankton photosynthetic activity and acclimation status. Measurements were carried out at two time scales (daily and annual) using the Pulse Amplitude Modulated fluorometry on samples taken in the coastal waters of a macrotidal ecosystem (the Strait of Dover, eastern English Channel). RLC and N-SSLC were compared under a wide range of environmental conditions and phytoplankton composition in order to define the best methodology to accurately capture short and long-term adjustments in the functioning of the photosynthetic apparatus. The relationships between the photosynthetic parameters extracted from RLC and N-SSLC were also studied to evaluate the possibility to use RLC to predict N-SSLC photosynthetic parameters and thus obtaining the acclimation status at steady state. At daily scale, the maximum electron transport rate and light saturation coefficient resulting from RLC (respectively, ETRm_RLC and Ek_RLC) were found to follow more closely short-term environmental light variations than ETRm and Ek resulting from N-SSLC (ETRm_N-SSLC and Ek_N-SSLC) did. RLC were thus able to detect rapid changes in photosynthetic activity that would have been overlooked with N-SSLC measurements. At annual scale, few differences were found between RLC and N-SSLC. Variations of ETRm and α derived from RLC and N-SSLC were very similar but absolute values were lower for RLC measurements. Because, at daily scale, RLC better capture the short-term changes in photosynthetic activity than N-SSLC do, using RLC to predict N-SSLC photosynthetic parameters and getting information about steady-state acclimation status is not possible at this time scale. However, this can be done at seasonal scale.
ABSTRACT L'utilisation des rapid light curves (RLC) et des steady state light curves (SSL... more ABSTRACT L'utilisation des rapid light curves (RLC) et des steady state light curves (SSLC), pour la caractérisation in situ de l'activité photosynthétique du phytoplancton, à différentes échelles de temps, a été comparée. La possibilité d'utiliser les paramètres photosynthétiques des RLC pour prédire ceux de SSLC a été évaluée. Les résultats montrent que les RLC sont un bon outil pour la caractérisation de l'activité photosynthétique à différentes échelles temporelles
Short-term changes in phytoplankton photosynthetic activity were studied during different periods... more Short-term changes in phytoplankton photosynthetic activity were studied during different periods of the years 2009 and 2010 in the coastal waters of a macrotidal ecosystem (the Strait of Dover, eastern English Channel). During each sampling period, samples were taken every 1.45 h., from sunrise to sunset, during at least 5 days distributed along a complete spring-neap tide cycle. The photosynthetic parameters were obtained by measuring rapid light curves using pulse amplitude modulated fluorometry and were related to environmental conditions and phytoplankton taxonomic composition. The maximum quantum yield (F v /F m) showed clear light-dependent changes and could vary from physiological maxima (0.68-0.60) to values close to 0.30 during the course of 1 day, suggesting the operation of photoprotective mechanisms. The maximum electron transport rate (ETR m) and maximal light utilization efficiency (a) were generally positively correlated and showed large diel variability. These parameters fluctuated significantly from hour to hour within each day and the intraday pattern of variation changed significantly among days of each sampling period. Stepwise multiple linear regressions analyses indicated that light fluctuations explained a part of this variability but a great part of variability stayed unexplained. F v /F m , ETR m and a were not only dependent on the light conditions of the sampling day but also on those of the previous days. A time lag of 3 days in the effect of light on ETR m and a variation was highlighted. At these time scales, changes in phytoplankton community structure seemed to have a low importance in the variability in photosynthetic parameters. The photoacclimation index E k showed a lower variability and was generally different from the incident irradiance, indicating a limited acclimation capacity with a poor optimization of light harvesting during the day. However, in well-mixed systems such as the Strait of Dover, the short-term photoacclimation is disrupted by the high level of variability in environmental conditions. Also, the variability observed in the present study can be associated with a particular kind of photosynthetic response: the ''E k-independent'' variability. The physiological basis of this photosynthetic response is largely unresolved and further researches on this subject are still required to better explain the dynamics of phytoplankton activity in the Strait of Dover.
In this study, we examined the possibility of using the FluoroProbe for monitoring the dynamics o... more In this study, we examined the possibility of using the FluoroProbe for monitoring the dynamics of the Haptophyte Phaeocystis globosa in the coastal waters of the eastern English Channel. The FluoroProbe was recalibrated by recording a new fingerprint for P. globosa and the use of this new fingerprint was tested through a series of laboratory and in situ experiments. The annual dynamics of P. globosa estimated using the FluoroProbe and by flow cytometry were similar. A strong relationship was found between the FluoroProbe estimates of P. globosa biomass expressed in terms of chlorophyll a equivalent per litre (eq. mg L 21) and flow cytometric cell counts (r ¼ 0.889, P , 0.001, n ¼ 121). The FluoroProbe can be used to detect the flagellated cells as well as the colonial cells of P. globosa but not to distinguish these two cell types in mixed assemblages. The use of the new fingerprint recorded for P. globosa improved the detection of Isochrysis sp. This suggests the possibility of using the FluoroProbe to monitor Haptophytes other than P. globosa by calibrating the device with species representative of the region of interest. However, it is important to note that the detection of P. globosa at the species level was possible in the eastern English Channel because it was the only Haptophyte species present with a biomass sufficient to be detected by the FluoroProbe. In areas where several Haptophyte species are simultaneously present, their discrimination will be impossible and in such situations the FluoroProbe can be used to monitor the dynamics of the combined Haptophyte group.
The temporal variability in phytoplankton photosynthetic activity was studied in the coastal wate... more The temporal variability in phytoplankton photosynthetic activity was studied in the coastal waters of the Strait of Dover and related to environmental conditions. Phytoplankton photosynthetic activity data collected from October 2008 and August 2010 at different time scales (hourly to interannual) using a nested sampling design are presented. Photosynthetic parameters including the maximum quantum yield (F v /F m), maximal light utilization efficiency (α), maximum electron transport rate (ETR m) and light saturation coefficient (E k) were measured using Pulse Amplitude Modulation (PAM) fluorometry. Information on the taxonomic composition of phytoplankton assemblages and physicochemical parameters were also collected. Marked changes in photosynthetic parameters were observed at the different time scales investigated. The variability of photosynthetic parameters at sub-seasonal scale (hourly to monthly) could be of the same order of magnitude as at seasonal scale. At short time scale (hour to week), there was no consistent pattern of diel periodicity in photosynthetic parameters. There was a decline of ETR m and α during the day as often as there was a peak at the maximum of irradiance. Light conditions were the main influencing factor on photosynthetic parameters at these time scales. The optimal use of incident irradiance seemed focused on between-days rather than within-day variability. At longer time scale (seasonal to interannual), close interplays between shifts in community taxonomic composition and changes in the physicochemical characteristics of the environment controlled the variability in photosynthetic parameters. Whatever the time scale and period of year considered, variability in photosynthetic parameters was "E k-independent". In well-mixed macrotidal ecosystems, such as the Strait of Dover, a nested sampling design allowing to characterize the short-(intraday and daily) as well as long-term variability (within months, monthly, seasonal, annual and interannual) in photosynthetic parameters is required to get a suitable picture of phytoplankton photosynthesis and avoid potential problems of aliasing.
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Papers by Emilie Houliez