@article {7195, title = {Evidence for better microphytobenthos dynamics in mixed sand/mud zones than in pure sand or mud intertidal flats (Seine estuary, Normandy, France)}, journal = {PLOS ONE}, volume = {15}, year = {2020}, month = {08/2020}, pages = { e0237211}, abstract = {Understanding the dynamics of microphytobenthos biomass and photosynthetic performances in intertidal ecosystems will help advance our understanding of how trophic networks function in order to optimize ecological management and restoration projects. The main objective of this study was to investigate microphytobenthic biomass and photosynthetic performances as a function of the sedimentary and environmental variabilities in the range of intertidal habitats in the downstream Seine estuary (Normandy, France). Our results highlight higher biomass associated with more stratified biofilms and better photosynthetic performances in areas characterized by a sand/mud mixture (40{\textendash}60\% of mud) compared to pure sand or pure mud environments. This type of sediment probably offers an efficient trade-off between the favorable characteristics of the two types of sediments (sand and mud) with respect to light penetration and nutrient accessibility. Moreover, the large quantities of exopolysaccharides produced in sand/mud mixtures emphasizes the functional role played by microphytobenthos in promoting sediment stability against erosion. This allows us to show that despite the strong increase in sand content of the downstream Seine estuary, intertidal flats are still productive since microphytobenthic biomass, photosynthetic performances and exopolysaccharides secretion are highest in sand-mud mixtures. This study also underlines the impact of ecosystem modifications due to human disturbance and climate change on the dynamics of key primary producers in estuaries.}, doi = {10.1371/journal.pone.0237211}, author = {Morelle, J{\'e}r{\^o}me and Pascal Claquin and Francis Orvain} } @article {5428, title = {Annual Phytoplankton Primary Production Estimation in a Temperate Estuary by Coupling PAM and Carbon Incorporation Methods}, journal = {Estuaries and Coasts}, year = {2018}, month = {02/2018}, abstract = {

Phytoplankton primary production varies considerably with environmental parameters especially in dynamic ecosystems like estuaries. The aimof this study was to investigate short-term primary production along the salinity gradient of a temperate estuary over the course of 1 year. The combination of carbon incorporation and fluorescence methods enabled primary production estimation at short spatial and temporal scales. The electron requirement for carbon fixation was investigated in relation with physical-chemical parameters to accurately estimate primary production at high frequency. These results combined with the variability of the photic layer allowed the annual estimation of primary production along the estuary. Phytoplankton dynamics was closely related to salinity and turbidity gradients, which strongly influenced cells physiology and photoacclimatation. The number of electrons required to fix 1 mol of carbon (C) was ranged between 1.6 and 25 mol electron mol C-1 with a mean annual value of 8 {\textpm} 5 mol electron mol C-1. This optimum value suggests that in nutrient replete conditions like estuaries, alternative electron flows are low, while electrons transfer from photosystem II to carbon fixation is highly efficient. A statistical model was used to improve the estimation of primary production from electron transport rate as a function of significant environmental parameters. Based on this model, daily carbon production in the Seine estuary (France) was estimated by considering light and photic zone variability. A mean annual daily primary production of 0.12 {\textpm} 0.18 g C m-2 day-1 with a maximum of 1.18 g C m-2 day-1 in summer was estimated which lead to an annual mean of 64.75 g C m-2 year-1. This approach should be applied more frequently in dynamic ecosystems such as estuaries or coastal waters to accurately estimate primary production in those valuable ecosystems.

}, keywords = {High frequency . Electron requirement for carbon fixation . Electron transport rate (ETR) . Seine estuary}, author = {Morelle, J{\'e}r{\^o}me and Mathilde Schapira and Francis Orvain and Riou, Philippe and Pascal Jean Lopez and Duplessix, Olivier and Rabiller, Emilie and Maheux, Franc and Simon, Benjamin and Pascal Claquin} } @article {5586, title = {Dynamics of exopolymeric carbon pools in relation with phytoplankton succession along the salinity gradient of a temperate estuary (France)}, journal = {Estuarine, Coastal and Shelf Science}, volume = {209}, year = {2018}, pages = {18-29}, abstract = {

In parallel to phytoplankton community dynamics, transparent exopolymeric particles (TEP) and exopolymeric
substances (EPS) were investigated along the salinity gradient of a temperate estuary (Seine estuary, Normandy,
France) over the course of a year. The phytoplankton community was mainly dominated by marine diatom
species (especially Skeletonema sp., Nitzschia sp., and Paralia sulcata) associated with a spring bloom of picoeukaryotes
and the development of Cryptophyceae in summer. The decreases in species richness and salinity were
correlated along the estuary and a significant exponential relationship between species richness and primary
production was identified. Concentrations of TEP and EPS (soluble and bound carbohydrates) are highly dynamic
in this estuary and can reach respectively 69 mgC L-1, and 33 mgC L-1. TEP distribution was mainly
related to physical factors (hydrodynamics, maximum turbidity zone formation and sediment resuspension)
probably produced by stressed or dying phytoplankton, while EPS appeared to be excreted during the phytoplankton
spring bloom. Soluble and bound EPS appear to be related to Skeletonema sp. and Cryptophyceae occurrences.
This paper presents the dynamic pattern of these carbon pools, which play an important role in the
trophic network and influence the flocculation processes involved in the fate of both organic and inorganic
matter.

}, keywords = {Exopolymeric substances Species, Nanophytoplankton, Picophytoplankton, richness}, author = {Morelle, J{\'e}r{\^o}me and Mathilde Schapira and Fran{\c c}oise, Sylvaine and Courtay Ga{\"e}lle and Francis Orvain and Pascal Claquin} } @article {5434, title = {Electron requirements for carbon incorporation along a diel light cycle in three marine diatom species}, journal = {Photosynthesis Research}, year = {2018}, pages = {1-14}, abstract = {

Diatoms account for about 40\% of primary production in highly productive ecosystems. The development of a new generation of fluorometers has made it possible to improve estimation of the electron transport rate from photosystem II, which, when coupled with the carbon incorporation rate enables estimation of the electrons required for carbon fixation. The aim of this study was to investigate the daily dynamics of these electron requirements as a function of the diel light cycle in three relevant diatom species and to apprehend if the method of estimating the electron transport rate can lead to different pictures of the dynamics. The results confirmed the species-dependent capacity for photoacclimation under increasing light levels. Despite daily variations in the photosynthetic parameters, the results of this study underline the low daily variability of the electron requirements estimated using functional absorption of the photosystem II compared to an estimation based on a specific absorption cross section of chlorophyll a. The stability of the electron requirements throughout the day would suggest it is potentially possible to estimate high-frequency primary production by using autonomous variable fluorescence measurements from ships-of-opportunity or moorings, without taking potential daily variation in this parameter into consideration, but this result has to be confirmed on natural phytoplankton assemblages. The results obtained in this study confirm the low electron requirements of diatoms to perform photosynthesis, and suggest a potential additional source of energy for carbon fixation, as recently described in the literature for this class.

}, doi = {https://doi.org/10.1007/s11120-018-0491-2}, url = {https://link.springer.com/article/10.1007\%2Fs11120-018-0491-2}, author = {Morelle, J{\'e}r{\^o}me and Pascal Claquin} } @article {5435, title = {A simple, user friendly tool to readjust raw PAM data from field measurements to avoid over- or underestimating of microphytobenthos photosynthetic parameters}, journal = {Journal of Experimental Marine Biology and Ecology}, volume = {503}, year = {2018}, pages = {136-146}, abstract = {

Intertidal mudflats are among the most productive ecosystems and microphytobenthic (MPB) biofilms play a key role in primary production. MPB primary production varies at short spatial and temporal scales. Accurate measurements thus require rapid non-intrusive methods like pulse amplitude modulate (PAM) fluorescence. However, the effect of granulometry and chl a concentration profile in light attenuation on irradiance and on fluorescence signal in the photic layer need to be taken into account when primary production is estimated using PAM. We propose a tool to readjust raw photosynthetic parameters (rETRmax, α, Ik) estimated from PAM measurements on the field, to avoid over- or underestimation. To develop the tool, we used models previously designed by K{\"u}hl and J{\o}rgensen (1992), Ser{\^o}dio (2004) and Forster and Kromkamp (2004) by integrating the chl a distribution profiles and sediment granulometry from pure sand to pure mud. The sensitivity of the correction to sediment granulometry and the shape of chl a profile were evaluated theoretically using a typical fluorescence data set obtained using PAM measurements. Our results confirm the importance of accounting for both the chl a profile and sediment granulometry when estimating a light attenuation coefficient. We show that, with the same chl a profile, the photosynthetic parameters are more underestimated in mud than in a sandy environment. Thus, granulometry and the chl a profile need to be systematically quantified and used to correct raw data measured in field studies using PAM before estimating photosynthetic parameters. The numerical tool is available as an e-document that is simple and easy to apply to any PAM data.

}, doi = {https://doi.org/10.1016/j.jembe.2018.02.007}, url = {https://www.sciencedirect.com/science/article/pii/S0022098117303325}, author = {Morelle, J{\'e}r{\^o}me and Francis Orvain and Pascal Claquin} } @article {5136, title = {Dynamics of phytoplankton productivity and exopolysaccharides (EPS and TEP) pools in the Seine Estuary (France, Normandy) over tidal cycles and over two contrasting seasons}, journal = {Marine Environmental Research}, year = {2017}, month = {09/2017}, author = {Morelle, J{\'e}r{\^o}me and Mathilde Schapira and Pascal Claquin} } @article {3413, title = {Interactive effects of irradiance and temperature on growth and domoic acid production of the toxic diatom Pseudo-nitzschia australis (Bacillariophyceae)}, journal = {Harmful Algae}, volume = {39}, year = {2014}, pages = {232-241}, abstract = {The influence of temperature and light on the growth, physiology and domoic acid (DA) production of the pennate toxic diatom Pseudo-nitzschia australis isolated from the English Channel was studied in semicontinuous culture. The effects of eight irradiances (35{\textendash}400 mmol photons m2 s-1) and a temperature gradient (3.5{\textendash}25.5 8C) were investigated. The highest growth rates (0.47{\textendash}0.83 d-1) were observed between 18.6 and 13.5 8C, with an optimum irradiance for growth at 100 mmol photons m2 s-1. A decrease in the optimum growth temperature was observed with an increase in irradiance. Cell chlorophyll a content decreased at both low and high extreme temperatures and high irradiances. Stable and high values of Fv/Fm ratios below 21.8C highlight the great acclimation capacity of P. australis, which may explain its wide biogeographic distribution. The strain studied produced DA without nutrient limitation and during exponential growth although at lower levels than in other studies (0.15{\textendash} 2.0 pg DA cell-1). Results underline the importance of light{\textendash}temperature interactions for growth and DA production. Toxin production increased with increasing temperature and light, and DA production increased exponentially with the growth rate. These results show that DA is not only produced under nutrient stress or by unhealthy cells in P. australis. This study underlines the need to take the ability of P. australis to produce DA during the exponential growth into consideration to understand the link between toxin production and bloom dynamics. These results will not only help explore the processes involved, but also help parameterize future models of growth and DA production especially for P. australis.}, keywords = {Domoic acid, Growth Irradiance, Pseudo-nitzschia australis, Temperature}, author = {Thorel, Maxine and Juliette Fauchot and Morelle, J{\'e}r{\^o}me and Raimbault, V and Le Rou, B and Miossec, C and Kientz-Bouchard, V and Pascal Claquin} }