Modelling the effect of vertical mixing on bottle incubations for determining in situ phytoplankton dynamics. I. Growth rates

Reliable estimates of in situ phytoplankton growth rates are central to understanding the dynamics of aquatic ecosystems. A common approach for estimating in situ growth rates is to incubate natural phytoplankton assemblages in clear bottles at fixed depths or irradiance levels and measure the change in chlorophyll a (Chl) over the incubation period (typically 24 h). Using a modelling approach, we investigate the accuracy of these Chl-based methods focussing on 2 aspects: (1) in a freely mixing surface layer, the cells are typically not in balanced growth, and with photoacclimation, changes in Chl may yield different growth rates than changes in carbon; and (2) the in vitro methods neglect any vertical movement due to turbulence and its effect on the cells' light history. The growth rates thus strongly depend on the incubation depth and are not necessarily representative of the depth-integrated in situ growth rate in the freely mixing surface layer. We employ an individual based turbulence and photosynthesis model, which also accounts for photoacclimation and photo - inhibition, to show that the in vitro Chl-based growth rate can differ both from its carbon-based in vitro equivalent and from the in situ value by up to 100%, depending on turbulence intensity, optical depth of the mixing layer, and incubation depth within the layer. We make recommendations for choosing the best depth for single-depth incubations. Furthermore we demonstrate that, if incubation bottles are being oscillated up and down through the water column, these systematic errors can be significantly reduced. In the present study, we focus on Chl-based methods only, while productivity measurements using carbon-based techniques (e.g. 14C) are discussed in Ross et al. (2011; Mar Ecol Prog Ser 435:33-45). © Inter-Research 2011

Modulation of ecdysal cyst and toxin dynamics of two Alexandrium (Dinophyceae) species under small-scale turbulence

Some dinoflagellate species have shown different physiological responses to certain turbulent conditions. Here we investigate how two levels of turbulent kinetic energy dissipation rates (epsilon = 0.4 and 27 cm(2) s(-3)) affect the PSP toxins and ecdysal cyst dynamics of two bloom forming species, Alexandrium minutum and A. catenella. The most striking responses were observed at the high epsilon generated by an orbital shaker. In the cultures of the two species shaken for more than 4 days, the cellular GTX(1+4) toxin contents were significantly lower than in the still control cultures. In A. minutum this trend was also observed in the C(1+2) toxin content. For the two species, inhibition of ecdysal cyst production occurred during the period of exposure of the cultures to stirring (4 or more days) at any time during their growth curve. Recovery of cyst abundances was always observed when turbulence stopped. When shaking persisted for more than 4 days, the net growth rate significantly decreased in A. minutum (from 0.25 +/- 0.01 day(-1) to 0.19 +/- 0.02 day(-1)) and the final cell numbers were lower (ca. 55.4%) than in the still control cultures. In A. catenella, the net growth rate was not markedly modified by turbulence although under long exposure to shaking, the cultures entered earlier in the stationary phase and the final cell numbers were significantly lower (ca. 23%) than in the control flasks. The described responses were not observed in the experiments performed at the low turbulence intensities with an orbital grid system, where the population development was favoured. In those conditions, cells appeared to escape from the zone of the influence of the grids and concentrated in calmer thin layers either at the top or at the bottom of the containers. This ecophysiological study provides new evidences about the sensitivity to high levels of small-scale turbulence by two life cycle related processes, toxin production and encystment, in dinoflagellates. This can contribute to the understanding of the dynamics of those organisms in nature

Assessing risks and mitigating impacts of harmful algal blooms on mariculture and marine fisheries

Aquaculture is the fastest growing food sector globally and protein provisioning from aquaculture now exceeds that from wild capture fisheries. There is clear potential for the further expansion of marine aquaculture (mariculture), but there are associated risks. Some naturally occurring algae can proliferate under certain environmental conditions, causing deoxygenation of seawater, or releasing toxic compounds (phycotoxins), which can harm wild and cultured finfish and shellfish, and also human consumers. The impacts of these so‐called harmful algal blooms (HABs) amount to approximately 8 $billion/yr globally, due to mass mortalities in finfish, harvesting bans preventing the sale of shellfish that have accumulated unsafe levels of HAB phycotoxins and unavoided human health costs. Here, we provide a critical review and analysis of HAB impacts on mariculture (and wild capture fisheries) and recommend research to identify ways to minimise their impacts to the industry. We examine causal factors for HAB development in inshore versus offshore locations and consider how mariculture itself, in its various forms, may exacerbate or mitigate HAB risk. From a management perspective, there is considerable scope for strategic siting of offshore mariculture and holistic Environmental Approaches for Aquaculture, such as offsetting nutrient outputs from finfish farming, via the co‐location of extractive shellfish and macroalgae. Such pre‐emptive, ecosystem‐based approaches are preferable to reactive physical, chemical or microbiological control measures aiming to remove or neutralise HABs and their phycotxins. To facilitate mariculture expansion and long‐term sustainability, it is also essential to evaluate HAB risk in conjunction with climate change

Editorial: Chemically Mediated Interactions Between Marine Macrophytes and Microbes

Is it well-accepted that communication among organisms including land plants and aquatic macrophytes in terrestrial and aquatic ecosystems is largely achieved using information-conveying chemicals or “infochemicals” (Saha et al., 2019) which should be seen as a chemical “language” of life. Marine macrophytes and phytoplankton are dominant primary producers in marine ecosystems worldwide (e.g., Behrenfeld et al., 2001). They produce oxygen and form the base of food webs, are ecosystem engineers, and provide ecologically and economically valuable functions and services (e.g., Holdt and Kraan, 2011; Sarker et al., 2020; review by Pierella Karlusich et al., 2020). Phytoplankton and macrophytes are not single isolated entities but establish intimate relationships between them as well as with non-photosynthetic microbes (including bacteria, fungi, viruses) forming holobionts. These interactions in turn influence carbon and nutrient cycling, regulate the productivity and dynamics of aquatic food webs, and affect ocean–atmosphere fluxes of climatically relevant gases like dimethylsulphide and greenhouse gases like halocarbons. Associations and interactions between photosynthetic and non-photosynthetic organisms are chemically-mediated and are dependent on “cross-talk” infochemicals as well. However, our knowledge on the chemical “language of life” in aquatic ecosystems is still incipient (when compared to terrestrial environment). We do not know which infochemicals facilitate or inhibit the preferential attachment of macrophytes by microbes senso lato (i.e., including photosynthetic microalgae and cyanobacteria and heterotrophic bacteria), whether the selected macroalgae can stimulate the production of particular phycotoxins, whether microbes produce compounds (and if so, which chemicals) that act as deterrent of macrophytes grazing. Given the important role that the rapidly undergoing climate-driven changes (rising temperature, acidification, hypoxia, desalination) are playing in the aquatic ecosystems, potential modifications on such chemically mediated interactions (Schmidt and Saha, 2020) cannot be discarded. Identifying infochemicals and understanding their role have been challenging mainly by technical limitation. However, the emergence of cutting edge technical advances in the fields of analytical chemistry, cell biology, and the “omics” resources offer nowadays the possibilities to achieve rapid progress into the field of chemically mediated algae-microbe interactions under the present oceans. This Research Topic ensembles seven research articles and one review paper aimed at advancing our knowledge of the chemically mediated macroalgae—microalgae—microbe interactions. A plethora of commercial and environmental applications may rise from a better understanding of the interactions among marine macroalgae (seaweeds) and associated microbes. For example, Burgunter-Delamare et al. conducted an exhaustive characterization of the genomes-sequencing Saha et al. Editorial: Chemically Mediated Marine Macrophyte-Microbe Interactions of 10 bacteria associated to the model brown alga Ecotocarpus siliculosus. Also, the genome-based reconstruction of their metabolic networks was conducted. The potential metabolic activities were then compared with metabolites produced by the macroalga. This allowed to predict which bacteria could facilitate the growth of the macroalgae. From the most promising consortia, some preliminary co-culture experiments were conducted testing the exchange of selected chemicals between alga and bacteria suggesting beneficial metabolites exchanges in the holobiont. Califano et al. investigated to what extent Integrated Multi-trophic Aquaculture (IMTA) influences the microbiome associated with the commercially important green alga Ulva rigida, comparing diversity, and taxonomic composition of wild vs. IMTA-grown algae and surrounding water. Amplicon Sequence Variants (ASVs) revealed that prokaryotic richness was higher in aquaculture water than on wild samples, and in both cases, richness was also higher in water than on Ulva samples. Aquaculture thus promoted the presence of known morphogenesis-inducing bacteria, suggesting that IMTA may shape the microbial community of cultured Ulva, including previously undetected taxa with unknown traits. This knowledge can facilitate the establishment of sustainable and environmentally friendly aquaculture. On the other hand, a better understanding on how marine macroalgae deter undesired epibiotic growth may lead to the development of new, environmentally safer antifouling paints (Da Gama et al., 2014; Saha et al., 2017). Bioassayguided fractionation of glycolipids from the brown seaweed Sargassum vulgare led to the isolation of three sub-fractions that demonstrated promising antifouling activity toward marine bacteria and microalgae (Plouguerné et al.). The main compounds in these fractions are monogalactosyldiacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG), and sulfoquinovosyldiacylglycerols (SQDG). These compounds appear to mediate microbial colonization of this macrophyte. Following this line, Ternon et al. characterized the surface metabolome and explored the bioactivity of surface extracts of four macroalgae, Dictyota dichotoma, Dictyota spiralis, Taonia atomaria, and Padina pavonica, that are common substrates of microalgae, including the toxic dinoflagellate Ostreopsis cf. ovata. Laboratory experiments combined with the analysis of the eukaryotic diversity (using 18S rRNA gene metabarcoding) of the organisms attached to the macroalgae in situ indicated that D. dichotoma could be the most bioactive macroalga, causing negative physiological responses on O. cf. ovata. However, the proliferation of O. cf. ovata depends on complex and multiple ecological factors. In fact, the blooms of this microalga may constitute a paradigm of the chemical ecology, due to the wide diversity of chemically driven responses exhibited by other microand macroorganisms exposed to Ostreopsis proliferations, as comprehensively reviewed by Pavaux et al. Ostreopsis produces toxins and attaches to the substrates (macroalgae, rocks, sand) by secreted mucopolysaccharides. These biomolecules may be involved in allelopathy and competitive interactions with the microbiota and predators’ deterrence leading to Ostreopsis blooms and also involved in the negative impacts on human health and certain benthic macrofauna. However, innovative tools and realistic experiments are needed to understand the dynamics and ecotoxicity of the Ostreopsis blooms and other benthic toxic dinoflagellates. With this objective, Tarazona-Janampa et al. using molecular and chemical tools characterized a wide range of bacterial assemblages associated to Prorocentrum lima species complex. In this case, the complex experiments conducted did not provide evidence that allelopathic interactions among the toxic microalgae and bacteria could play a definable role in the growth and toxin production by P. lima species complex. The results suggest that other internal physiological processes or environmental factors can modulate the toxicity of this microalgal blooms. Awiderangeofmicrobes,frombacteriatofungi,alsocolonize the internal tissues of macroalgae. However, chemically mediated interactions of macroalgae with these endosymbiotic microbes remain poorly explored to date and were addressed by Vallet et al. Novel α-hydroxy-γ-butenolides isolated from the obligate marine fungus Paradendryphiella salina were found to interfere with bacterial quorum sensing. Comparative metabolomics revealed the presence of α-hydroxy- γ -butenolides among all the P. salina strains isolated from different hosts. Also, a high metabolic variability related to the alga-host species was found, highlighting the key role of microbial chemical communication that may occur within the tissue of the macroalgal holobiont. Along with marine macro- and microalgae, seagrasses are also known to engage in chemically mediated interactions with surface associated microbes (Guan et al., 2017). Such defense can be dynamic in nature and has been recently shown to fluctuate at a seasonal scale (Guan et al., 2019). However, how such defense and the responsible infochemicals may respond to climate change induced stressors like marine heatwaves is not known yet. To answer this, Guan et al. demonstrate how climate change imposed stressors like marine heatwaves may alter the infochemicals produced by the seagrass Zostera marina in the Western Baltic. In a mesocosm study where the authors simulated near natural heatwaves, the capacity to deter microbial colonizers was to be significantly up-regulated in Z. marina from heatwave treatments (with one or three heatwaves)incomparisontoZ.marinaundercontrolconditions, suggesting defense regulation of Z. marina in response to marine heatwaves

Tres lecciones científicas que nos deja el coronavirus

El coronavirus SARS-CoV-2 y la enfermedad COVID-19 son una experiencia dolorosa, pero también nos proporciona excelentes lecciones de ciencia. Entre ellas destacaríamos tres: La salud del planeta es también nuestra salud [...]Peer reviewe

Marine harmful algal blooms, human health and wellbeing : challenges and opportunities in the 21st century

Author Posting. © Marine Biological Association of the United Kingdom, 2015. This is the author's version of the work. It is posted here by permission of Marine Biological Association of the United Kingdom for personal use, not for redistribution. The definitive version was published in Journal of the Marine Biological Association of the United Kingdom 96 (2016): 61-91, doi:10.1017/S0025315415001733.Microalgal blooms are a natural part of the seasonal cycle of photosynthetic organisms in marine ecosystems. They are key components of the structure and dynamics of the oceans and thus sustain the benefits that humans obtain from these aquatic environments. However, some microalgal blooms can cause harm to humans and other organisms. These harmful algal blooms (HABs) have direct impacts on human health and negative influences on human wellbeing, mainly through their consequences to coastal ecosystem services (valued fisheries, tourism and recreation) and other marine organisms and environments. HABs are natural phenomena, but these events can be favoured by anthropogenic pressures in coastal areas. Global warming and associated changes in the oceans could affect HAB occurrences and toxicity as well, although forecasting the possible trends is still speculative and requires intensive multidisciplinary research. At the beginning of the 21st century, with expanding human populations, particularly in coastal and developing countries, there is an urgent need to prevent and mitigate HABs’ impacts on human health and wellbeing. The available tools to address this global challenge include maintaining intensive, multidisciplinary and collaborative scientific research, and strengthening the coordination with stakeholders, policymakers and the general public. Here we provide an overview of different aspects to understand the relevance of the HABs phenomena, an important element of the intrinsic links between oceans and human health and wellbeing.The research was funded in part by the UK Medical Research Council (MRC) and UK Natural Environment Research Council (NERC) for the MEDMI Project; the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Environmental Change and Health at the London School of Hygiene and Tropical Medicine in partnership with Public Health England (PHE), and in collaboration with the University of Exeter, University College London and the Met Office; and the European Regional Development Fund Programme and European Social Fund Convergence Programme for Cornwall and the Isles of Scilly (University of Exeter Medical School). EB was supported by the CTM2014-53818-R project, from the Spanish Government (MINECO). KDA was in receipt of funding from the BBSRC-NERC research programme for multidisciplinary studies in sustainable aquaculture: health, disease and the environment. P. Hess was supported by Ifremer (RISALTOX) and the Regional Council of the Pays de la Loire (COSELMAR). Porter Hoagland was supported by the US National Science Foundation under NSF/CNH grant no. 1009106.2016-05-2

Harmful Algal Blooms. A scientific summary for policy makers

What is a Harmful Algal Bloom (HAB)? Photosynthetic algae support healthy aquatic ecosystems by forming the base of the food web, fixing carbon and producing oxygen. Under certain circumstances, some species can form high-biomass and/or toxic proliferations of cells (or “blooms”), thereby causing harm to aquatic ecosystems, including plants and animals, and to humans via direct exposure to water-borne toxins or by toxic seafood consumption. Ecosystem damage by high-biomass blooms may include, for instance, disruption of food webs, fish-killing by gill damage, or contribution to low oxygen “dead-zones” after bloom degradation. Some species also produce potent natural chemicals (toxins) that can persist in the water or enter the food web, leading to illness or death of aquatic animals and/or human seafood consumers

The roses ocean and human health chair: A new way to engage the public in oceans and human health challenges

Involving and engaging stakeholders is crucial for studying and managing the complex interactions between marine ecosystems and human health and wellbeing. The Oceans and Human Health Chair was founded in the town of Roses (Catalonia, Spain, NW Mediterranean) in 2018, the fruit of a regional partnership between various stakeholders, and for the purpose of leading the way to better health and wellbeing through ocean research and conservation. The Chair is located in an area of the Mediterranean with a notable fishing, tourist, and seafaring tradition and is close to a marine reserve, providing the opportunity to observe diverse environmental conditions and coastal and maritime activities. The Chair is a case study demonstrating that local, collaborative, transdisciplinary, trans-sector, and bottom-up approaches offer tremendous opportunities for engaging coastal communities to help support long-lasting solutions that benefit everyone, and especially those living by the sea or making their living from the goods and services provided by the sea. Furthermore, the Chair has successfully integrated most of its experts in oceans and human health from the most prestigious institutions in Catalonia. The Chair focuses on three main topics identified by local stakeholders: Fish and Health; Leisure, Health, and Wellbeing; and Medicines from the Sea. Led by stakeholder engagement, the Chair can serve as a novel approach within the oceans and human health field of study to tackle a variety of environmental and public health challenges related to both communicable and non-communicable diseases, within the context of sociocultural issues. Drawing on the example provided by the Chair, four principles are established to encourage improved participatory processes in the oceans and human health field: bottom-up, “think local”, transdisciplinary and trans-sectorial, and “balance the many voices”.info:eu-repo/semantics/publishedVersio

The Roses Ocean and Human Health Chair: A New Way to Engage the Public in Oceans and Human Health Challenges

Involving and engaging stakeholders is crucial for studying and managing the complex interactions between marine ecosystems and human health and wellbeing. The Oceans and Human Health Chair was founded in the town of Roses (Catalonia, Spain, NW Mediterranean) in 2018, the fruit of a regional partnership between various stakeholders, and for the purpose of leading the way to better health and wellbeing through ocean research and conservation. The Chair is located in an area of the Mediterranean with a notable fishing, tourist, and seafaring tradition and is close to a marine reserve, providing the opportunity to observe diverse environmental conditions and coastal and maritime activities. The Chair is a case study demonstrating that local, collaborative, transdisciplinary, trans-sector, and bottom-up approaches offer tremendous opportunities for engaging coastal communities to help support long-lasting solutions that benefit everyone, and especially those living by the sea or making their living from the goods and services provided by the sea. Furthermore, the Chair has successfully integrated most of its experts in oceans and human health from the most prestigious institutions in Catalonia. The Chair focuses on three main topics identified by local stakeholders: Fish and Health; Leisure, Health, and Wellbeing; and Medicines from the Sea. Led by stakeholder engagement, the Chair can serve as a novel approach within the oceans and human health field of study to tackle a variety of environmental and public health challenges related to both communicable and non-communicable diseases, within the context of sociocultural issues. Drawing on the example provided by the Chair, four principles are established to encourage improved participatory processes in the oceans and human health field: bottom-up, "think local", transdisciplinary and trans-sectorial, and "balance the many voices"

Future HAB science: Directions and challenges in a changing climate

There is increasing concern that accelerating environmental change attributed to human-induced warming of the planet may substantially alter the patterns, distribution and intensity of Harmful Algal Blooms (HABs). Changes in temperature, ocean acidification, precipitation, nutrient stress or availability, and the physical structure of the water column all influence the productivity, composition, and global range of phytoplankton assemblages, but large uncertainty remains about how integration of these climate drivers might shape future HABs. Presented here are the collective deliberations from a symposium on HABs and climate change where the research challenges to understanding potential linkages between HABs and climate were considered, along with new research directions to better define these linkages. In addition to the likely effects of physical (temperature, salinity, stratification, light, changing storm intensity), chemical (nutrients, ocean acidification), and biological (grazer) drivers on microalgae (senso lato), symposium participants explored more broadly the subjects of cyanobacterial HABs, benthic HABs, HAB effects on fisheries, HAB modelling challenges, and the contributions that molecular approaches can bring to HAB studies. There was consensus that alongside traditional research, HAB scientists must set new courses of research and practices to deliver the conceptual and quantitative advances required to forecast future HAB trends. These different practices encompass laboratory and field studies, long-term observational programs, retrospectives, as well as the study of socioeconomic drivers and linkages with aquaculture and fisheries. In anticipation of growing HAB problems, research on potential mitigation strategies should be a priority. It is recommended that a substantial portion of HAB research among laboratories be directed collectively at a small sub-set of HAB species and questions in order to fast-track advances in our understanding. Climate-driven changes in coastal oceanographic and ecological systems are becoming substantial, in some cases exacerbated by localized human activities. That, combined with the slow pace of decreasing global carbon emissions, signals the urgency for HAB scientists to accelerate efforts across disciplines to provide society with the necessary insights regarding future HAB trends