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Extracellular signals are reported to mediate chemical cross-talk among pelagic microbes, including microalgal prey and predators. Water-soluble mediator compounds play a crucial role in extracellular communication which is vital for prey recognition, attraction, capture, and predator deterrence. A range of exo-metabolites including oxylipins and vitamins are released by prey in response to grazing stress. The temporal dynamics of such exo-metabolites largely remains unknown, especially in large-scale cultivation of microalgae such as closed or open ponds. In open ponds, infestation of predators is almost inevitable but highly undesirable due to the imminent threat of culture collapse. The early production of exo-metabolites emitted by microalgal prey in response to predator attack could be leveraged as diagnostic markers of possible culture collapse. This study uses an untargeted approach for temporal profiling of Dunaliella tertiolecta-specific exo-metabolites under grazing pressure from Oxyrrhis marina. We report 24 putatively identified metabolites, belonging to various classes such as short peptides, lipids, indole-derivatives, and free amino acids, as potential markers of grazing-mediated stress. In addition, this study outlines a clear methodology for screening of exo-metabolites in marine algal samples, the analysis of which is frequently hindered by high salt concentrations. In future, a chemistry-based targeted detection of these metabolites could enable a quick and on-site screening of predators in microalgal cultures.

Defining the physiological traits that characterise phytoplankton involves comparison with related organisms in benthic habitats Comparison of survival time in darkness under natural conditions requires more information Gas vesicles and flagella as mechanisms of upward movement relative to surrounding water allowing periodic vertical migration are not confined to plankton although buoyancy changes related to compositional changes of a large central vacuole may be restricted to plankton Benthic microalgae have the same range of photosynthetic pigments as phytoplankton it is not clear if there are differences in the rate of regulation and acclimation of photosynthetic machinery to variations in irradiance for phytoplankton and for microphytobenthos There are inadequate data to determine if responses to variations in frequency or magnitude of changes in the supply of inorganic carbon nitrogen or phosphorus differ between phytoplankton and benthic microalgae Phagophotomixotrophy and osmophotomixotrophy occur in both phytoplankton and benthic microalgae Further progress in identifying physiological traits specific to phytoplankton requires more experimentation on benthic microalgae that are closely related to planktonic microalgae with attention to whether the benthic algae examined have as far as can be determined never been planktonic during their evolution or are derived from planktonic ancestors 2022 by the authors Licensee MDPI Basel Switzerland

Abstract Environmental change and biodiversity loss are but two of the complex challenges facing conservation practitioners and policy makers. Relevant and robust scientific knowledge is critical for providing decision-makers with the actionable evidence needed to inform conservation decisions. In the Anthropocene, science that leads to meaningful improvements in biodiversity conservation, restoration and management is desperately needed. Conservation Physiology has emerged as a discipline that is well-positioned to identify the mechanisms underpinning population declines, predict responses to environmental change and test different in situ and ex situ conservation interventions for diverse taxa and ecosystems. Here we present a consensus list of 10 priority research themes. Within each theme we identify specific research questions (100 in total), answers to which will address conservation problems and should improve the management of biological resources. The themes frame a set of research questions related to the following: (i) adaptation and phenotypic plasticity; (ii) human–induced environmental change; (iii) human–wildlife interactions; (iv) invasive species; (v) methods, biomarkers and monitoring; (vi) policy, engagement and communication; (vii) pollution; (viii) restoration actions; (ix) threatened species; and (x) urban systems. The themes and questions will hopefully guide and inspire researchers while also helping to demonstrate to practitioners and policy makers the many ways in which physiology can help to support their decisions.

Salinity is one of the significant factors that affect growth and cellular metabolism, including photosynthesis and lipid accumulation, in microalgae and higher plants. Microchloropsis gaditana CCMP526 can acclimatize to different salinity levels by accumulating compatible solutes, carbohydrates, and lipids as energy storage molecules. We used proteomics to understand the molecular basis for acclimation of M. gaditana to increased salinity levels [55 and 100 PSU (practical salinity unit)]. Correspondence analysis was used for the identification of salinity-responsive proteins (SRPs). The highest number of salinity-induced proteins was observed in 100 PSU. Gene ontology enrichment analysis revealed a separate path of acclimation for cells exposed to 55 and 100 PSU. Osmolyte and lipid biosynthesis were upregulated in hypersaline conditions. Concomitantly, lipid oxidation pathways were also upregulated in hypersaline conditions, providing acetyl-CoA for energy metabolism through the tricarboxylic acid cycle. Carbon fixation and photosynthesis were tightly regulated, while chlorophyll biosynthesis was affected in hypersaline conditions. Importantly, temporal proteome analysis of salinity-induced M. gaditana revealed vital SRPs which could be used for engineering salinity resilient microalgal strains for improved productivity in hypersaline culture conditions.

Microalgae are major primary producers in aquatic environments, and many synthesize an array of industrially important biomolecules such as pigments, lipids and proteins. As a result, there is considerable interest in and effort into growing algae for industrial purposes. An economical method to produce a large amount of biomass is the use of the open-raceway pond cultivation platform. However, the nature of the cultivation and the nutrient-rich profile of such cultures attract contaminants such as zooplankton predators, which can result in a sudden culture crash. For effective pond management, an early indicator of grazer presence is needed to implement timely interventions. Currently available tools are offline, time-consuming and dependent on predator concentration. This study explores grazing-mediated changes in photosynthetic parameters during infestation of Dunaliella tertiolecta cultures by the heterotrophic dinoflagellate Oxyrrhis marina and the ciliate Euplotes sp. A significant reduction in non-photochemical quenching levels 24–48 h prior to the crash was observed in both bulk and single-cell prey samples. An increasing rate of grazer ingestion correlated with decreasing non-photochemical quenching levels as the culture progressed towards the crash. The reductions in the non-photochemical quenching levels were consistent in grazing cultures at different prey cell concentrations. Although the maximum photosynthetic yield remained unaltered, maximum relative electron transport rates were enhanced and the light-harvesting efficiency, alpha, reduced in comparison to controls. We suggest that, along with traditional methods, non-photochemical quenching monitoring could be used as a part of integrative pest management to minimize predator outbreaks.

Inorganic carbon assimilation in algae depends ultimately on the activity of ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) and the Calvin-Benson-Bassham Cycle (Photosynthetic Carbon Reduction Cycle; PCRC). The kinetic characteristics of the different forms of Rubisco found in algae and cyanobacteria are such that under present day levels of CO2 and oxygen, inefficiencies in carbon assimilation, involving, inter alia, photorespiration would occur. Given this, achievement of significant rates of net photosynthesis necessitates the operation of CO2 concentrating mechanisms (CCMs) to elevate CO2 concentrations, and increase CO2:O2 ratios at the active site of Rubisco. The biochemical, C4 photosynthesis, CCM appears to be limited to the marine ulvophycean alga Udotea flabellum and one species of a marine diatom (Thalassiosira weisflogii) as well as in some seagrasses and freshwater macrophytes. With few exceptions all other algae and the cyanobacteria possess a biophysical CCM, based on active transport of inorganic carbon. Despite many years of research into CCMs, there is still a good deal of misunderstanding about what comprises reliable and robust evidence for CCM activity. By definition, there needs to be a demonstrable net positive gradient of CO2 in > CO2 out. In addition, cells with active CCMs have K0.5CO2 values for DIC-dependent photosynthesis less than that for their Rubiscos. Other features such as isotope discrimination can also be useful, with cells using CO2 diffusion alone showing ∆13C values ~ −30‰ and discrimination values becoming less negative as CCM activity increases. However, the presence of gene sequences for, or even expressed activity of, enzymes such as PEP carboxylase, are not good indicators of operation of C4 photosynthesis. It is a common misconception that possession of external carbonic anhydrase can alone result in CO2 accumulation. CCMs involve active transport of bicarbonate and/or CO2. In cyanobacteria this occurs at the

Oxygen uptake in illuminated photosynthetic algae can be measured using 18O2 or (with some reservations) photosystem II electron flux measured by fluorescence corrected for electron flux to sinks other than O2. Water-water cycles, involve photosystem II removing electrons from water to produce O2. Water-water cycles involving photosystem I as well as photosystem II use the Mehler-peroxidase reaction, or flavodiiron protein, in the O2 reduction reactions, with pumping of 3 H+ per electron. The other known water-water cycle involves only photosystem II, with the plastid (plastoquinol) terminal oxidase transferring electrons to O2, pumping of 1 H+ per electron. Return flux of the pumped H+ through the CFOCF1 ATP synthase can supplement or replace ATP from cyclic electron flow and oxidative phosphorylation in equating the supply of NADPH and ATP to the metabolic need. A further light-dependent O2 process in algae is the energy-consuming process of photorespiration metabolising 2-phosphoglycolate from Rubisco oxygenase activity. The rate of photorespiration relative to that of photosynthesis depends on the CO2:O2 selectivity of Rubisco, and the steady-state CO2:O2 ratio at the site of Rubisco. In most algae a CO2 concentrating mechanism limits photorespiration by increasing the CO2:O2 ratio at the site of Rubisco, though, in cyanobacteria at least, some photorespiratory flux is essential. The minimum rate of mitochondrial respiration in the light is set by the requirement in biosynthesis of carbon skeletons produced only in the tricarboxylic acid cycle; higher rates may occur to supply ATP. There are problems in allocating O2 uptake in the light among the various pathways; the use of inhibitors, mutants or knockouts of a particular pathway is undermined by the possibility, or even likelihood, of compensatory reactions.

© 2019 CSIRO. 'Multiple drivers' (also termed 'multiple stressors') is the term used to describe the cumulative effects of multiple environmental factors on organisms or ecosystems. Here, we consider ocean acidification as a multiple driver because many inorganic carbon parameters are changing simultaneously, including total dissolved inorganic carbon, CO2, HCO3-, CO32-, H+ and CaCO3 saturation state. With the rapid expansion of ocean acidification research has come a greater understanding of the complexity and intricacies of how these simultaneous changes to the seawater carbonate system are affecting marine life. We start by clarifying key terms used by chemists and biologists to describe the changing seawater inorganic carbon system. Then, using key groups of non-calcifying (fish, seaweeds, diatoms) and calcifying (coralline algae, coccolithophores, corals, molluscs) organisms, we consider how various physiological processes are affected by different components of the carbonate system.

© The Author 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: journals.permissions@oup.com. CO2-concentrating mechanisms (CCMs), based either on active transport of inorganic carbon (biophysical CCMs) or on biochemistry involving supplementary carbon fixation into C4 acids (C4 and CAM), play a major role in global primary productivity. However, the ubiquitous CO2-fixing enzyme in autotrophs, Rubisco, evolved at a time when atmospheric CO2 levels were very much higher than today and O2 was very low and, as CO2 and O2 approached (by no means monotonically), today's levels, at some time subsequently many organisms evolved a CCM that increased the supply of CO2 and decreased Rubisco oxygenase activity. Given that CO2 levels and other environmental factors have altered considerably between when autotrophs evolved and the present day, and are predicted to continue to change into the future, we here examine the drivers for, and possible timing of, evolution of CCMs. CCMs probably evolved when CO2 fell to 2-16 times the present atmospheric level, depending on Rubisco kinetics. We also assess the effects of other key environmental factors such as temperature and nutrient levels on CCM activity and examine the evidence for evolutionary changes in CCM activity and related cellular processes as well as limitations on continuity of CCMs through environmental variations.

This book covers the state-of-the-art of microalgae physiology and biochemistry (and the several –omics). It serves as a key reference work for those working with microalgae, whether in the lab, the field, or for commercial applications. It is aimed at new entrants into the field (i.e. PhD students) as well as experienced practitioners. It has been over 40 years since the publication of a book on algal physiology. Apart from reviews and chapters no other comprehensive book on this topic has been published. Research on microalgae has expanded enormously since then, as has the commercial exploitation of microalgae. This volume thoroughly deals with the most critical physiological and biochemical processes governing algal growth and production.

Photosynthesis by marine diatoms contributes substantially to global biogeochemical cycling and ecosystem productivity. It is widely accepted that diatoms are extremely sensitive to changes in Fe availability, with numerous in situ experiments demonstrating rapid growth and increased export of elements (e. g. C, Si and Fe) from surface waters as a result of Fe addition. Less is known about the effects of Fe enrichment on the phenotypes of diatoms, such as associated changes in nutritional value - furthermore, data on taxon-specific responses are almost non-existent. Enhanced supply of nutrient-rich waters along the coast of the sub-antarctic Kerguelen Island provide a valuable opportunity to examine the responses of phytoplankton to natural Fe enrichment. Here we demonstrate the use of synchrotron radiation Fourier Transform Infrared (SR-FTIR) microspectroscopy to analyse changes in the macromolecular composition of diatoms collected along the coast and plateau of Kerguelen Island, Southern Ocean. SR-FTIR microspectroscopy enabled the analysis of individual diatom cells from mixed communities of field-collected samples, thereby providing insight into in situ taxon-specific responses in relation to changes in Fe availability. Phenotypic responses were taxon-specific in terms of intraspecific variability and changes in proteins, amino acids, phosphorylated molecules, silicate/silicic acid and carbohydrates. In contrast to some previous studies, silicate/silicic acid levels increased under Fe enrichment, in conjunction with increases in carbohydrate stores. The highly abundant taxon Fragilariopsis kerguelensis displayed a higher level of phenotypic plasticity than Pseudo-nitzschia spp., while analysis of the data pooled across all measured taxa showed different patterns in macromolecular composition compared to those for individual taxon. This study demonstrates that taxon-specific responses to Fe enrichment may not always be accurately reflected by bulk community meas

Chlorella spp. are robust chlorophyte microalgal species frequently used in mass culture. The pH optimum for growth is close to neutrality; at this pH, theoretically little energy is required to maintain homeostasis. In the present study, we grew Chlorella fusca cells in an open, outdoor, thin-layer cascade photobioreactor (TLC), under ambient photon flux at the theoretically preferred pH (7.2), and let the culture pass the exponential growth phase. Using pH drift experiments, we show that an alkalization to pH 9 supported photosynthesis in the TLC. The increased photosynthetic activity under alkaline conditions was a pH-dependent effect, and not a dissolved inorganic carbon (DIC) concentration- or light intensity-dependent effect. Re-acidification (in one step or in increments) lowered gross oxygen production and increased non-photochemical quenching in short-term experiments. Gross oxygen production and electron transport rates in PSII were uncoupled during the pH perturbation experiments. Electron transport rates were only marginally affected by pH, whereas oxygen production rates decreased with acidification. Alternative electron pathways, electron donation at the plastid terminal oxidase and state-transitions are discussed as a potential explanation. Because cell material from the TLC was not operating at maximal capacity, we propose that alkalization can support photosynthesis in challenged TLC systems.