Determination of optical markers of cyanobacterial physiology from fluorescence kinetics

Compared to other methods to monitor and detect cyanobacteria in phytoplankton populations, fluorometry gives rapid, robust and reproducible results and can be used in situ. Fluorometers capable of providing biomass estimates and physiological information are not commonly optimized to target cyanobacteria. This study provides a detailed overview of the fluorescence kinetics of algal and cyanobacterial cultures to determine optimal optical configurations to target fluorescence mechanisms that are either common to all phytoplankton or diagnostic to cyanobacteria. We confirm that fluorescence excitation channels targeting both phycocyanin and chlorophyll a associated to the Photosystem II are required to induce the fluorescence responses of cyanobacteria. In addition, emission channels centered at 660, 685 and 730 nm allow better differentiation of the fluorescence response between algal and cyanobacterial cultures. Blue-green actinic light does not yield a robust fluorescence response in the cyanobacterial cultures and broadband actinic light should be preferred to assess the relation between ambient light and photosynthesis. Significant variability was observed in the fluorescence response from cyanobacteria to the intensity and duration of actinic light exposure, which needs to be taken into consideration in field measurements

Optimising Multispectral Active Fluorescence to Distinguish the Photosynthetic Variability of Cyanobacteria and Algae

This study assesses the ability of a new active fluorometer, the LabSTAF, to diagnostically assess the physiology of freshwater cyanobacteria in a reservoir exhibiting annual blooms. Specifically, we analyse the correlation of relative cyanobacteria abundance with photosynthetic parameters derived from fluorescence light curves (FLCs) obtained using several combinations of excitation wavebands, photosystem II (PSII) excitation spectra and the emission ratio of 730 over 685 nm (Fo(730/685)) using excitation protocols with varying degrees of sensitivity to cyanobacteria and algae. FLCs using blue excitation (B) and green–orange–red (GOR) excitation wavebands capture physiology parameters of algae and cyanobacteria, respectively. The green–orange (GO) protocol, expected to have the best diagnostic properties for cyanobacteria, did not guarantee PSII saturation. PSII excitation spectra showed distinct response from cyanobacteria and algae, depending on spectral optimisation of the light dose. Fo(730/685), obtained using a combination of GOR excitation wavebands, Fo(GOR, 730/685), showed a significant correlation with the relative abundance of cyanobacteria (linear regression, p-value < 0.01, adjusted R2 = 0.42). We recommend using, in parallel, Fo(GOR, 730/685), PSII excitation spectra (appropriately optimised for cyanobacteria versus algae), and physiological parameters derived from the FLCs obtained with GOR and B protocols to assess the physiology of cyanobacteria and to ultimately predict their growth. Higher intensity LEDs (G and O) should be considered to reach PSII saturation to further increase diagnostic sensitivity to the cyanobacteria component of the community

Single-Turnover Variable Chlorophyll Fluorescence as a Tool for Assessing Phytoplankton Photosynthesis and Primary Productivity: Opportunities, Caveats and Recommendations

Phytoplankton photosynthetic physiology can be investigated through single-turnover variable chlorophyll fluorescence (ST-ChlF) approaches, which carry unique potential to autonomously collect data at high spatial and temporal resolution. Over the past decades, significant progress has been made in the development and application of ST-ChlF methods in aquatic ecosystems, and in the interpretation of the resulting observations. At the same time, however, an increasing number of sensor types, sampling protocols, and data processing algorithms have created confusion and uncertainty among potential users, with a growing divergence of practice among different research groups. In this review, we assist the existing and upcoming user community by providing an overview of current approaches and consensus recommendations for the use of ST-ChlF measurements to examine in-situ phytoplankton productivity and photo-physiology. We argue that a consistency of practice and adherence to basic operational and quality control standards is critical to ensuring data inter-comparability. Large datasets of inter-comparable and globally coherent ST-ChlF observations hold the potential to reveal large-scale patterns and trends in phytoplankton photo-physiology, photosynthetic rates and bottom-up controls on primary productivity. As such, they hold great potential to provide invaluable physiological observations on the scales relevant for the development and validation of ecosystem models and remote sensing algorithms

Assessing the photo-physiology of cyanobacteria using active fluorescence

Eutrophication and the impacts of climate change are responsible for the increased occurrence of harmful algae blooms. In lakes and reservoirs, cyanobacteria blooms pose particular risk to ecosystems, humans and animals due to the occurrence of toxin-producing species. Several methods exist to monitor cyanobacteria, which vary in cost, time and accuracy. Fluorescence methods developed to monitor cyanobacterial abundance already give rapid, robust and reproducible results. Discrimination between cyanobacteria and algae in fluorescence methods is based on their photosynthetic pigment content, but due to overlapping pigment absorption signatures, the interpretation of fluorescence signals is consequently not straightforward. In this thesis, a range of fluorescence markers were tested on the ability to assess and predict cyanobacteria physiology and growth. Hyperspectral laboratory experiments with algal and cyanobacteria cultures revealed that excitation wavebands centred on 445 nm and 615 nm, and emission wavebands at 660, 685 and 730 nm allow the best differentiation between cyanobacteria and algae. Broadband actinic light should be preferred to assess the relation between ambient light and photosynthesis. Based on these results, a new multispectral active fluorometer (LabSTAF) was tested to assess the physiology and growth of cyanobacteria in reservoirs exhibiting annual blooms. Fluorescence light curves obtained with a green-orange-red (GOR) and a blue (B) excitation protocol were found to follow cyanobacteria and algae physiology, respectively. The fluorescence emission ratio of photosystem I over II was also significantly correlated with the relative abundance of cyanobacteria. Excitation spectra further distinguish the presence of distinct pigment groups. Finally, the ability of the LabSTAF to determine cyanobacteria growth from photosynthetic parameters was demonstrated on natural samples brought into nutrient replete conditions. ETR (electron transport rate) and Pmax (maximum specific photosynthetic rate) were found to predict phytoplankton growth by up to 3-4 days, with excitation protocols GOR and B indicating the dominant phytoplankton group

Les champignons dans la bande-dessinée

LILLE2-BU Santé-Recherche (593502101) / SudocSudocFranceF

Reproductive biology of a small amphidromous shrimp Atyoida serrata on Reunion Island, south-west Indian Ocean

International audienc

A user guide for the application of single turnover active chlorophyll fluorescence for phytoplankton productivity measurements

This document represents the collective efforts of SCOR Working Group 156, ‘Active Chlorophyll Fluorescence for Autonomous Measurements of Global Marine Primary Productivity’. The group was established in 2019, bringing together researchers and instrument manufacturers from 10 countries and 5 continents, with the goal of developing standards of best practice for the application of single turnover active chlorophyll fluorescence (ST-ChlF) to examine phytoplankton productivity. We focused our efforts on single turnover methods, which are most commonly used in phytoplankton research, while recognizing that other approaches, including Pulse Amplitude Modulation (PAM) fluorescence techniques, are also employed with macro-algae, corals and terrestrial plants. Over the past two years, our group has worked to build consensus around best practice for the collection, analysis and archiving of ST-ChlF data from a variety of aquatic environments. We aim to facilitate wide-spread use of ST-ChlF methods by the international research community, and have thus far focused our work on several key activities outlined in the Working Group’s terms of reference