Photosynthetic performance of microphytobenthos from intertidal mudflats in Aiguillon Bay (Atlantic coast, France) and non-tidal coastal shallows of Puck Bay (Baltic Sea, Poland)

Dans les écosystèmes littoraux, les communautés microphytobenthiques sont soumises à des conditions environnementales qui peuvent être extrêmes en particulier en ce qui concerne l'intensité lumineuse. Les mécanismes de protection mis en place dépendent étroitement du type d'habitat où se développent ces communautés et cette thèse a pour objectifs d'analyser les caractéristiques de l'activité photosynthétique et les mécanismes de protection développés par des assemblages microphytobenthiques dans deux écosystèmes littoraux très différents : les vasières intertidales atlantiques de la Baie de L'Aiguillon (France) et la lagune côtière non tidale de Puck Bay dans la Mer Baltique (Władysławowo, Pologne). Pour réaliser ces objectifs, trois études ont été réalisées : (1) la description des communautés microphytobenthiques, (2) la caractérisation de leur activité photosynthétique et (3) l'analyse des mécanismes de photoinhibition et de photoprotection.La structure taxonomique du microphytobenthos a été décrite en se basant sur des observations en microscopie optique et sur la mesure des caractéristiques des pigments photosynthétiques par chromatographie liquide à haute performance (HPLC). L'activité photosynthétique a été étudiée par des méthodes de microrespirométrie volumétrique et de spectrofluorométrie de la chlorophylle a. Les mécanismes de photoinhibition et de photoprotection ont été étudiés par fluorométrie en modulation d'amplitude pulsée (PAM).Les résultats obtenus nous ont permis de montrer que :1) Les communautés atlantiques sont fortement dominées par des diatomées épipéliques, alors que le microphytobenthos de la Mer Baltique est plus diversifié et comporte, outre des diatomées, une large part de cyanobactéries,2) Les microphytobenthos atlantique est bien acclimaté à des valeurs d'intensités lumineuses plutôt faibles, alors que les communautés de la Mer Baltique ont encore une bonne activité photosynthétique à de fortes irradiances,3) Les diatomées atlantiques présentent une plus forte photoinhibition que les microalgues de la Baltique,4) L'activité photosynthétique des communautés microphytobenthiques non perturbées montre un des rythmes circadien et tidal, qui semblent être contrôlés par des facteurs endogènes, qui mettent en jeu des adaptations comportementales comme la migration verticale pour les diatomées atlantiques,5) En ce qui concerne le microphytobenthos de la Mer Baltique, qui n'a pas de capacité migratoire, la photoprotection est assurée en premier lieu par la mise en jeu de processus physiologiques. Nous avons pu montrer la très grande flexibilité du photsystème PSII qui est capable de suivre très rapidement les changements à court terme de lumière ambiante.The scope of this thesis includes the characteristics and comparison of photosynthetic activity and photoprotection mechanisms of microphytobenthos assemblages inhabiting the Atlantic intertidal mudflats of Aiguillon Bay (Esnandes, France) and the littoral zone of the Baltic Sea in non-tidal Puck Bay (Władysławowo, Poland). In order to accomplish the main aims of the work the following tasks were carried out: (1) characterization of microphytobenthic assemblages; (2) characterization of their photosynthetic activity and (3) description of photoinhibition and photoprotective mechanisms. The structure of microphytobenthos was described based on observation of the material in light microscope (LM) and through the characteristics of photosynthetic pigments using high performance liquid chromatography (HPLC). Photosynthetic activity was described using various methods including classical (volumetric micro-respirometer) and modern (chlorophyll a fluorescence) ones. In addition, the measurements of variable fluorescence were also used to study photoinhibition and photoprotective mechanisms. Based on the obtained results it was stated that:1.) the Atlantic assemblages were strongly dominated by epipelic diatoms, while the Baltic microphytobenthos was more diverse and cyanobacteria, next to diatoms, were also very important component,2.) it was shown that the Atlantic microphytobenthos was well acclimated to rather low light intensities, while the Baltic assemblages showed good utilization of higher irradiance,3.) the Atlantic diatoms were more susceptible to photoinhibition than the Baltic microalgae,4.) the photosynthetic activity described for the undisturbed microphytobenthos communities revealed circadian and circatidal rhythms, which seemed to be controlled by endogenous factors, supporting diatoms’ behavioural adaptations i.e., vertical migration,5.) in case of the Baltic microphytobenthos, the lack of the ability to move caused their physiological processes the first line of defence against excess irradiances. The analysis revealed extreme flexibility of PSII which was able to follow rapidly the short-term changes in ambient ligh

Effects of the Ionic Liquid [BMIM]Cl on the Baltic Microphytobenthic Communities

Ionic liquids (IL) are regarded as the solution to the modern world’s need to create and use compounds that exhibit a range of desirable properties while having a low environmental impact. However, recent reports are shattering the image of ionic liquids as environmentally friendly substances, especially in relation to the aquatic environment, revealing their potentially toxic effects. To assess the potential environmental impact of ILs, we conducted an experiment involving 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), a substance considered to be the least hazardous among the imidazolium chloride ILs, on Baltic microphytobenthic communities. Microphytobenthos collected from the environment was tested under controlled laboratory conditions, and both the cell counts and the chloroplast condition were used as endpoints. It was shown that [BMIM]Cl at concentrations of 10−3 and 10−2, considered safe based on a cumulative impact assessment, has a negative effect on the condition of the microalgal cells and causes a reduction in population size. Although, under the influence of [BMIM]Cl, only a small proportion of the species was eliminated from the communities, only two species among those important to the communities showed resistance to this compound and eventually began to dominate the communities

Ecotoxicological Studies on the Effect of Roundup® (Glyphosate Formulation) on Marine Benthic Microalgae

Glyphosate is a very effective herbicide and the main active ingredient in Roundup®—the most extensively used herbicide in the world. Since glyphosate is highly water soluble it reaches water bodies easily in surface water runoff. This prompted us to undertake an experiment to evaluate the effects of glyphosate in Roundup® on natural communities of marine microphytobenthos. Microphytobenthos communities were obtained from the environment, and after transporting them to the laboratory and acclimatizing them, they were tested under controlled conditions. Changes in microphytobenthos composition and structure and the deteriorating condition of the cells of community-forming organisms (assessed by analyzing changes in chloroplast shape) were used to assess the impact of Roundup® on endpoints. The tests indicated that microphytobenthic communities were relatively resistant to herbicide. The species richness of the communities probably enabled them to rebuild effectively. Sensitive species were replaced by those more tolerant of glyphosate. Only at the highest glyphosate concentration (8.5 g·dm−3) tested was a strong negative effect noted that limited community abundance and eliminated some of the organisms. The dominant diatoms in the communities were replaced by intensively developing cyanobacteria, which ultimately comprised nearly 60% of all the cells observed in the communities

Effects of the Ionic Liquid [BMIM]Cl on the Baltic Microphytobenthic Communities

Ionic liquids (IL) are regarded as the solution to the modern world’s need to create and use compounds that exhibit a range of desirable properties while having a low environmental impact. However, recent reports are shattering the image of ionic liquids as environmentally friendly substances, especially in relation to the aquatic environment, revealing their potentially toxic effects. To assess the potential environmental impact of ILs, we conducted an experiment involving 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), a substance considered to be the least hazardous among the imidazolium chloride ILs, on Baltic microphytobenthic communities. Microphytobenthos collected from the environment was tested under controlled laboratory conditions, and both the cell counts and the chloroplast condition were used as endpoints. It was shown that [BMIM]Cl at concentrations of 10−3 and 10−2, considered safe based on a cumulative impact assessment, has a negative effect on the condition of the microalgal cells and causes a reduction in population size. Although, under the influence of [BMIM]Cl, only a small proportion of the species was eliminated from the communities, only two species among those important to the communities showed resistance to this compound and eventually began to dominate the communities

Identification of Cyanometabolites and Toxicity Assessment of Cyanobacteria Isolates from Chosen Polish Eutrophic Waters and Polar Glaciers

Cyanobacteria have the ability to produce various types of bioactive compounds. Some of them can exert toxic effects on aquatic fauna, including daphnids, which are sensitive organisms that respond fast to toxins. Therefore, these crustaceans are useful for aquatic toxicity assessment. In this study, several dozen cyanobacterial strains isolated from different types of water bodies were analyzed for the presence of anabaenopeptins (APs), anatoxin-a (ATX-a), β-methylamino-L-alanine (BMAA), cylindrospermopsin (CYN), microcystins (MCs), nodularin (NOD), saxitoxin (STX) using immunoassay and chromatographic techniques. We also investigated the toxicity of extracts and filtrates from 40-days-old cyanobacterial cultures using biotests with D. magna and D. pulicaria. Analytical techniques revealed the presence of the cyanometabolites studied in isolates of Aphanizomenon (APs, BMAA, CYN, STX), Planktothrix (APs, MCs), Cuspidothrix (ATX-a, CYN) and Limnothrix (BMAA). Polar strains were free of examined compounds. Biotests revealed a reduction in Daphnia survival in response to some extracts and filtrates. It was also found in the case of one polar strain. However, there was no clear pattern indicating that extracts/filtrates from strains with identified toxic compounds reduced Daphnia survival more than other strains. This suggests that other yet unknown toxic compounds are at play. This study was financed by the Polish National Agency for Academic Exchange (project no. PPN/BEK/2020/1/00241), and partially by the National Science Centre in Poland (project no. UMO-2020/39/D/NZ8/02436)