Embedded Files
Improving interpretation of fluorescence measurements on natural microphytobenthic bioflms
Improving interpretation of fluorescence measurements on natural microphytobenthic bioflms
Introduction
Intertidal mudflats are among the most productive ecosystems, with microphytobenthic biofilms playing a key role as primary producers. However, the photosynthetic activity of microphytobenthos varies over short spatial and temporal scales, requiering rapid and non-intrusive measurement methods such as pulse amplitude modulation (PAM) fluorescence. However, it is crucial to consider the effects of granulometry and chlorophyll a concentration vertical profiles on the attenuation of light and fluorescence signals in the photic layer when estimating natural microphytobenthic photosynthesis using PAM devices.
In this context, part of my research, included in the BARBES and PROUESSE projects, focused on improving our understanding and treatment of fluorescence measurements for natural microphytobenthic biofilms.
In the context previously described in the introduction, one of my research aimed at developing a numerical tool to readjust raw fluorescence measurements obtained from field PAM measurements, in order to avoid potential over- or underestimation of photosynthetic parameters.
The numerical tool developed was based on previous models and incorporates chlorophyll a distribution profiles and sediment granulometry ranging from pure sand to pure mud. Results confirm the critical need to account for both the chl a profile and sediment granulometry when estimating light attenuation coefficients, and underscore the necessity of systematically quantifying both factors to accurately correct raw PAM data before estimating photosynthetic parameters. Specifically, the results highlighted that for similar chl a profiles, photosynthetic parameters tend to be more underestimated in mud environments compared to sandy ones.
The tool and results were published in 'Journal of Experimental Marine Biology and Ecology ' in 2018. Access to the paper
Following the development of the numerical tool, our subsequent study applied it to investigate the dynamics of microphytobenthos across various intertidal habitats in the downstream Seine estuary. This research aimed to understand how habitat variation influences microphytobenthos and their roles in trophic networks, which is crucial for optimizing ecological management and restoration efforts.
Our main findings reveal that microphytobenthos biomass and photosynthetic performance were higher in areas with a sand/mud mixture (40–60% mud) compared to pure sand or pure mud habitats. This sediment type likely provides an effective balance between the light penetration of sand and the nutrient availability of mud.
The results of this study were published in the journal 'PlosOne' in 2020. Access to the paper
Role of benthic ecosystem engineers on microphytobenthos dynamics
Role of benthic ecosystem engineers on microphytobenthos dynamics
Introduction
Microphytobenthos is most often the primary source of carbon for coastal soft-sediment communities, especially in intertidal and shallow subtidal environments. However, benthic macrofaunal organisms also influence microphytobenthic biomass, spatial distribution, and photosynthetic capacities through their feeding activity but also indirectly from their bioturbation activity, which regulates nutrient fluxes and sediment mixing. Understanding interactions between primary producers and ecosystem engineers, as well as biogeochemical variables, is crucial because it provides insights into how changes in benthic community structure and function can impact primary production and overall ecosystem health. This knowledge is essential for effective conservation and management strategies aimed at preserving the ecological balance and productivity of these vital coastal habitats.
In this context, part of my research, included in the PHARESEE project, focused on improving our knowledge of the role of benthic ecosystem engineers on microphytobenthic biofilms.
In the context previously described in the introduction, one of my research aimed at comparing experimentally the impacts of two distinct macrofaunal species (Hediste diversicolor and Scrobicularia plana) on microphytobenthic biomass and photosynthetic activity.
Our results revealed that S. plana, due to its intense bioturbative behavior, significantly limited microphytobenthos growth and photosynthetic activity, even at relatively low densities. In contrast, H. diversicolor had a minimal impact on microphytobenthos development, primarily due to its low level of direct consumption, while its bioirrigation activity most likely stimulated nutrient fluxes, consequently enhancing microphytobenthos growth and photosynthesis.
The results were published in the journal 'Marine Environmental Research' in 2021 Access to the paper
A second study confirming these results under different conditions was also published in 'Ecosystems' in 2023. Access to the paper
Following experimental studies, we investigated the effects of these macrofaunal species on sediment properties, biogeochemical variables, and microbial dynamics (including microphytobenthos, bacteria, and archaea) in an intertidal mudflat of the Seine Estuary by varying their abundances during both winter and late summer seasons.
Results showed that in winter, the presence of H. diversicolor significantly increased accretion and microbial activity, while S. plana showed no impact due to reduced activity at low temperatures. In summer, both species strongly influenced their environment but in contrasting ways: S. plana limited microbial growth and enhanced erosion, while H. diversicolor paromoted sediment accretion and microbial growth. This interdisciplinary study confirmed the critical roles of ecosystem engineers and emphasized the importance of considering them in the restoration of tidal flats to mitigate vulnerability risks.
The results were published in the journal 'Journal of Experimental Marine Biology and Ecology ' in 2023. Access to the paper
Understanding the photoprotective behavior of the motile benthic diatoms
Understanding the photoprotective behavior of the motile benthic diatoms
Introduction
Among microphytobenthos, raphid pennate diatoms have thrived in colonizing intertidal areas. These diatoms are capable of directed motility, which is hypothesized to be a major factor explaining their success and productivity in benthic habitats. Besides regular time- and tide-synchronized migrations, benthic diatoms have been hypothesized to perform phototaxis according to irradiance levels, allowing them to optimize their photosynthesis. However, despite the well-known vertical migration of benthic diatoms, some gaps in our knowledge persist. Some accepted hypotheses still need to be confirmed, and little is known about the cellular mechanisms triggering vertical migration in response to light detection.
In this context, part of my research, included in the SEARCHLIGHT project, focused on improving our knowledge on the photobehavior of benthic pennate diatom species.
In the context previously described in the introduction, the first study in which I had the opportunity to be involved aimed to better understand the role of motility in pennate diatoms in regulating light exposure through the development of a model to quantitatively characterize and compare the light environment of individual pennate diatom cells in intertidal estuarine sediments.
The results of this work suggest that epipelic diatoms benefit from a more stable light regime due to vertical migration, while epipsammic species experience a more variable and unstable light environment. This highlights that light-driven motility results in light niche construction through habitat selection.
The results were published in the journal 'Ecological Modelling' in 2023 Access to the paper
One of my study according to this topic aimed to test the hypothesis that benthic motile pennate diatoms optimize photosynthesis and minimize photoinhibitory damage through phototaxis by adjusting their position within a microscale light gradient.
To achieve this, a novel experimental approach was developed to concurrently study the behavior and photosynthetic activity of individual cells of the epipelic diatom species Craspedostauros britannicus.
The results supported the hypothesis for this species, showing that cells adjust their position to reduce light exposure under high-intensity conditions and combine motility with reversible non-photochemical quenching to avoid photoinhibition.
The findings of this study were published in the journal 'Microbial Ecology' in 2024. Access to the paper
Page updated
Google Sites
Report abuse