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The Benguela Upwelling System (BUS) is one of the world’s most productive ecosystems, supporting globally relevant pelagic fisheries. BUS marine community can change as a function of nutrients and omega-3 long chain polyunsaturated fatty acids (hereafter, omega-3) availability. Phytoplankton growth is supported by upwelled nitrate, a new source of nitrogen (N), or by recycled N forms such as ammonium. Preferential assimilation of one N form over another may lead to differences in omega-3 production between high and low food-quality species. This study evaluates how upwelling and the N source(s) used by phytoplankton influence omega-3 production. Sampling was conducted in the BUS at an anchor station sampled daily for 10 consecutive days. An upwelling event on days 5-6-7 supplied high concentrations of nutrients to surface waters, while pre- and post- upwelling the water column was well-stratified with low nutrient concentrations. Omega-3 and phytoplankton concentrations declined to ⁓zero during the upwelling event. Nanoplankton (2.7-10µm) were responsible for most of the productivity (30-95%) and relied on nitrate for their growth. Omega-3 concentrations at the surface reached peaks of 215.5 and 175.3µgL-1 pre- and post-upwelling, which were up to 10-times higher than previous measurements from the BUS. Pre-upwelling, non-diatom trophic markers were dominant, with a rapid switch (over just two days) to diatom trophic markers post-upwelling. This study defines the key role of upwelling in promoting phytoplankton omega-3 production, which is tightly coupled to the introduction of new-N during upwelling. The high concentrations of omega-3 reported suggest that global omega-3 production is largely underestimated.

The use of microalgae as a sustainable source of n-3 long-chain polyunsaturated fatty acids (LC-PUFA) as an alternative to fish oils from small pelagic fish (e.g., anchovy, sardine) has received growing interest in the past few years. The present study aimed to: (i) produce Aurantiochytrium mangrovei biomass by heterotrophic fermentation using a medium containing anaerobic digestion liquid effluent, and (ii) evaluate a biomass rich in n-3 LC-PUFA and good quality proteins as a feed ingredient for sea bass juveniles and larvae. Two 800 L bioreactors were used to produce Aurantiochytrium biomass in non-axenic conditions. Biomass was then filtered through a crossflow filtration system (300 Kda ceramic membrane) and freeze-dried. Sea bass juveniles (32.7 ± 4.2 g) were fed both a control diet and a diet containing 15% of freeze-dried A. mangrovei biomass for 38 days. Juvenile survival percentage was 90% on average in both dietary conditions. Similar growth was observed between fish fed with both diets, demonstrating the feasibility to replace 15% of a standard fish feed by Aurantiochytrium biomass. The liver of sea bass juveniles fed with the A. mangrovei diet contained significantly higher proportions of 22:6n-3, 22:5n-6, and 20:4n-6 than those fed with the control diet, while the proportions of 16:0, 16:1n-7, and 18:1n-9 were significantly lower. The secondary oxidation, as measured by malonylaldehyde (MDA) content, in the liver and muscle of juveniles fed with the microalgae diet tended to be higher than in fish fed the control diet, but the differences were not statistically significant. Although the larvae survival percentage was low for all the tanks after 41 days of rearing, the inclusion of 15% of hydrolyzed A. mangrovei biomass in the larvae micro-diet did not impair the development of sea bass larvae and only marginally affected their lipid composition. In the future, we have to further optimize a sustainable workflow between Aurantiochytrium cultivation and fish feed production and confirm the zootechnical and biochemical results.

In the open ocean and particularly in iron (Fe)-limited environment, copper (Cu) deficiency might limit the growth of phytoplankton species. Cu is an essential trace metal used in electron-transfer reactions, such as respiration and photosynthesis, when bound to specific enzymes. Some phytoplankton species, such as the diatom Pseudo-nitzschia spp. can cope with Cu starvation through adaptative strategies. In this study, we investigated the physiological strategies of the marine diatom P. delicatissima against Cu starvation. Compared to the control, Cu starvation inhibited growth by 35%, but did not induce any excess mortality. Despite the bottleneck measured in the electron flow of the photosynthetic chain, cells of P. delicatissima conserved their photosynthesis ability. This photosynthesis maintenance was accompanied by structural changes of membranes, where pigments and lipid composition were strongly modified. Diatoms also strongly modified their metabolism, by redirecting their C allocation to energy storage under the form of triglycerides. By maintaining essential metabolic functions and storing energy under the form of lipids, these physiological adaptations might be a strategy enabling this diatom to later bloom under the return of favorable nutritional condition.

International audience; Long-chain polyunsaturated fatty acids (LC-PUFA) are molecules produced at the basis of marine food webs and essential for ecosystem functioning. This study reports detailed fatty acid (FA) composition including the two LC-PUFA 20:5n-3 and 22:6n-3, in suspended organic matter (SPOM) from the upper 300 m collected in the Kerguelen Island region in the Southern Ocean during the post-bloom period (February–March 2018; project MOBYDICK). FA profiles were largely dominated by PUFA (53–69% of Total Fatty Acid, TFA) regardless of stations and among PUFA, proportions of LC-PUFA were especially high, making up 27–44% of TFA both in the ML and upper mesopelagic. 20:5n-3 and 22:6n-3 co-occurred in the ML as a result of the post-bloom phytoplankton community showing a mixed composition dominated by small size phytoplankton (prymnesiophytes and prasinophytes) supplying 22:6n-3, and with diatoms in lower proportions supplying 20:5n-3. Elevated levels of LC-PUFA were observed both inside the iron-fertilized area on the Kerguelen Plateau and downstream, and outside in High Nutrient Low Chlorophyll waters located upstream of the Plateau, and appeared unrelated to site. In the upper mesopelagic, both LC-PUFA were maintained at high relative proportions suggesting an efficient and possibly fast vertical transfer from the surface. Transfer with depth seems to proceed via distinct pathways according to LC-PUFA. 20:5n-3 may be exported along with diatoms, presumably in the form of large intact cells, aggregates as well as resting spores. For 22:6n-3, transfer may involve a channeling through the heterotrophic food web resulting in its association with fecal material at depth. Channeling of 22:6n-3 could involve heterotrophic protists such as dinoflagellates and ciliates grazing on small phytoplankton, as well as larger zooplankton such as copepods and salps, possibly feeding on microzooplankton and producing fecal pellets rich in 22:6n-3. According to LC-PUFA content, SPOM present throughout the upper water column (0–300 m) appeared of high nutritional quality both on- and off-plateau, and represented a valuable source of food for secondary consumers and suspension feeders.

Few estuaries remain unaffected by water management and altered freshwater deliveries. The Caloosahatchee River Estuary is a perfect case study for assessing the impact of altered hydrology on natural oyster reef (Crassostrea virginica) populations. The watershed has been highly modified and greatly enlarged by an artificial connection to Lake Okeechobee. Accordingly, to generate data to support water management recommendations, this study monitored various oyster biometrics over 15 years along the primary salinity gradient. Oyster reef densities were significantly affected by both prolonged high volume freshwater releases creating hyposaline conditions at upstream sites and by a lack of freshwater input creating hypersaline conditions at downstream sites. Low freshwater input led to an increase in disease caused by Perkinsus marinus and predation. Moderate (< 2000 cfs) and properly timed (winter/spring) freshets benefited oysters with increased gametogenesis, good larval mixing, and a reprieve from disease. If high volume freshets occurred in the late summer, extensive mortality occurred at the upstream site due to low salinity. These findings suggest freshwater releases in the late summer, when reproductive stress is at its peak and pelagic larvae are most vulnerable, should be limited to < 2000 cfs, but that longer freshets (1-3 weeks) in the winter and early spring (e.g., December-April) benefit oysters by reducing salinity and lessening disease intensity. Similar strategies can be employed in other managed systems, and patterns regarding the timing of high volume flows are applicable to all estuaries where the management of healthy oyster reefs is a priority.

International audience; Long-chain omega-3 fatty acids such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are health beneficial lipids found in high concentration in pelagic fishes, including Atlantic mackerel. While EPA and DHA are sensitive to oxidative degradation during fish storage and processing, post-mortem degradation in the first hours following fish death is poorly documented. In this study, we stored fish at two temperatures (2-4°C and 18-20°C) and monitored EPA+DHA content in dorsal fillet 6, 12 and 24 hours after fish death and after cooking (grill or steam). Storage duration was the most influencing factor, and EPA+DHA loss was faster at 18-20°C. Six hours after fish death, and regardless of storage temperature EPA+DHA content decreased by 1.3±1.3 mg.g-1 (9.6±9.5% of the initial content). EPA+DHA losses were highly variable among individuals, probably because of other sources of variability (e.g., sampling position). Handling between fishing operation and deep-frozen storage should be as short and as cool as possible to preserve EPA+DHA and for food safety. Regarding cooking, both EPA+DHA and mono-unsaturated fatty acids increased in grilled fillets.

The aetiological agent Perkinsus olseni is globally recognised as a major threat for shellfish production considering its wide geographical distribution across Asia, Europe, Australia and South America. Another species, Perkinsus chesapeaki, which has never been known to be associated with significant mortality events, was recently detected along French coasts infecting clam populations sporadically in association with P. olseni. Identifying potential cryptic infections affecting Ruditapes philippinarum is essential to develop appropriate host resource management strategies. Here, we developed a molecular method based on duplex real-time quantitative PCR for the simultaneous detection of these two parasites, P. olseni and P. chesapeaki, in the different clam tissues: gills, digestive gland, foot, mantle, adductor muscle and the rest of the soft body. We firstly checked the presence of possible PCR inhibitors in host tissue samples. The qPCR reactions were inhibited depending on the nature of the host organ. The mantle and the rest of the soft body have a high inhibitory effect from threshold of host gDNA concentration of 2 ng.µL−1, the adductor muscle and the foot have an intermediate inhibition of 5 ng.µL−1, and the gills and digestive gland do not show any inhibition of the qPCR reaction even at the highest host gDNA concentration of 20 ng.µL−1. Then, using the gills as a template, the suitability of the molecular technique was checked in comparison with the Ray’s Fluid Thioglycolate Medium methodology recommended by the World Organisation for Animal Health. The duplex qPCR method brought new insights and unveiled cryptic infections as the co-occurrence of P. olseni and P. chesapeaki from in situ tissue samples in contrast to the RFTM diagnosis. The development of this duplex qPCR method is a fundamental work to monitor in situ co-infections that will lead to optimised resource management and conservation strategies to deal with emerging diseases.

Dinoflagellates from the globally distributed genus Alexandrium are known to produce both paralytic shellfish toxins (PST) and uncharacterized bioactive extracellular compounds (BEC) with allelopathic, ichthyotoxic, hemolytic and cytotoxic activities. In France, blooms of Alexandrium minutum appear generally during the spawning period of most bivalves. These blooms could therefore alter gametes and/or larval development of bivalves, causing severe issues for ecologically and economically important species, such as the Pacific oyster Crassostrea (=Magallana) gigas. The aim of this work was to test the effects of three strains of A. minutum producing either only PST, only BEC, or both PST and BEC upon oyster gametes, and potential consequences on fertilization success. Oocytes and spermatozoa were exposed in vitro for 2 h to a range of environmentally realistic A. minutum concentrations (10–2.5 × 104 cells mL−1). Following exposure, gamete viability and reactive oxygen species (ROS) production were assessed by flow cytometry, spermatozoa motility and fertilization capacities of both spermatozoa and oocytes were analysed by microscopy. Viability and fertilization capacity of spermatozoa and oocytes were drastically reduced following exposure to 2.5 × 104 cells mL−1 of A. minutum. The BEC-producing strain was the most potent strain decreasing spermatozoa motility, increasing ROS production of oocytes, and decreasing fertilization, from the concentration of 2.5 × 103 cells mL−1. This study highlights the significant cellular toxicity of the BEC produced by A. minutum on oyster gametes. Physical contact between gametes and motile thecate A. minutum cells may also contribute to alter oyster gamete integrity. These results suggest that oyster gametes exposure to A. minutum blooms could affect oyster fertility and reproduction success.

International audience; Swordfish Xiphias gladius is a large pelagic fish distributed worldwide and exploited for human consumption, however there is limited knowledge about its reproductive biology, especially regarding lipid dynamic in gonads. In teleost fish, reproductive success and offspring survival are associated to lipid availability for gamete synthesis. This study investigated the lipid composition, including lipid classes and fatty acids (FA) of cell membrane and reserve lipids (i.e., polar and neutral lipids, respectively; PL and NL), along female and male gonad development of a swordfish population from waters surrounding Corsica Island in the Mediterranean Sea. Overall, swordfish gonads contained 20% of total FA), while 20:5n-3 and 20:4n-6 were minor (3-6% of total FA) and varied little with maturation. 22:6n-3 and 18:1n-9 were selectively allocated to the ovarian maturation (increased in concentration and in proportion with maturation) until spawning. Finally, swordfish gonads might represent a good food source for humans given that 150 g of swordfish ovaries can cover the daily requirements in omega-3 for humans, but research on pollutants should also be conducted to evaluate their implications on the reproduction output of this species, and on the safety of swordfish gonads for human consumption.

International audience; Food characteristics are amongst the most influential factors determining the fish life history traits as quantitative and qualitative changes in individuals' diet can lead to a decline in the energy allocated to their growth, and hence influence natural populations' characteristics. The size-at-age and weight of European sardines (Sardina pilchardus) in the Bay of Biscay (BoB) have decreased substantially over the last decade, especially for the youngest age classes, and the factors underlying such changes have not yet been identified. We therefore analysed the fatty acid (FA) composition in the neutral (NL) and polar (PL) lipids in samples collected across the BoB to determine whether the diet of sardines changes with their ages. We found that the total FA contents in both lipid fractions varied mainly with the sampling locations and age. Indeed, sardines aged 1 and 2 years living in South BoB had particularly high contents in FA specific to non-diatom phytoplankton, while older sardines living in the Northern part had higher total FA content and more FA specific to copepods. These differences probably resulted from differences in prey availability and to a lesser extend a change in feeding behaviour with age. The strong dependence of younger sardines’ diet to phytoplankton in spring suggests that changes in primary production may explain their decline in size-at-age. Finally, NL clearly reflect finest feeding variations in comparison to PL imprinted by diet variations at longer time scale. Future studies should consider separately NL and PL fractions.

WOS:000616240600001; International audience; Early life stages (ELS) of numerous marine invertebrates mustcope with man-made contaminants, including plastic debris, during their pelagic phase. Among the diversity of plastic particles, nano-sized debris, known as nanoplastics, can induce effects with severe outcomes in ELS of various biological models, including the Pacific oyster Crassostrea gigas. Here, we investigated the effects of a sub-lethal dose (0.1 mu g mL(-1)) of 50 nm polystyrene nanobeads (nano-PS) with amine functions on oyster embryos (24 h exposure) and we assessed consequences on larval and adult performances over two generations of oysters. Only a few effects were observed. Lipid analyses revealed that first-generation (G1) embryos exposed to nano-PS displayed a relative increase in cardiolipin content (+9.7%), suggesting a potential modification of mitochondrial functioning. G1-larvae issued from exposed embryos showed decreases in larval growth (-9%) and lipid storage (-20%). No effect was observed at the G1 adult stage in terms of growth, ecophysiological parameters (clearance and respiration rates, absorption efficiency), or reproductive outputs (gonadic development, gamete quality). Second generation (G2) larvae issued from control G1 displayed a significant growth reduction after G2 embryonic exposure to nano-PS (-24%) compared to control (as observed at the first generation), while no intergenerational effect was detected on G2 larvae issued from G1 exposed embryos. Overall, the present experimental study suggests a low incidence of a short embryonic exposure to nano-PS on oyster phenotypes along the entire life cycle until the next larval generation.

International audience; An important, but underappreciated, consequence of climate change is the reduction in crucial nutrient production at the base of the marine food chain: the long-chain omega-3 highly unsaturated fatty acids (n-3 HUFA). This can have dramatic consequences on consumers, such as fish as they have limited capacity to synthesise n-3 HUFA de novo. The n-3 HUFA, such as docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3), are critical for the structure and function of all biological membranes. There is increasing evidence that fish will be badly affected by reductions in n-3 HUFA dietary availability, however the underlying mechanisms remain obscure. Hypotheses for how mitochondrial function should change with dietary n-3 HUFA availability have generally ignored ATP production, despite its importance to a cell's total energetics capacity, and in turn, whole-animal performance. Here we (i) quantified individual variation in mitochondrial efficiency (ATP/O ratio) of muscle and (ii) examined its relationship with content in EPA and DHA in muscle membrane of a primary consumer fish, the golden grey mullet Chelon auratus, receiving either a high or low n-3 HUFA diet. Mitochondria of fish fed on the low n-3 HUFA diet had higher ATP/O ratio than those of fish maintained on the high n-3 HUFA diet. Yet, mitochondrial efficiency varied up about 2-fold among individuals on the same dietary treatment, resulting in some fish consuming half the oxygen and energy substrate to produce the similar amount of ATP than conspecific on similar diet. This variation in mitochondrial efficiency among individuals from the same diet treatment was related to individual differences in fatty acid composition of the membranes: a high ATP/O ratio was associated with a high content in EPA and DHA in biological membranes. Our results highlight the existence of interindividual differences in mitochondrial efficiency and its potential importance in explaining intraspecific variation in response to food chain changes.

The present study sought to characterize the synthesis pathways producing the essential polyunsaturated fatty acid (PUFA) 20:5n-3 (EPA). For this, the incorporation of 13C was experimentally monitored into 10 fatty acids (FA) during the growth of the diatom Chaetoceros muelleri for 24 h. Chaetoceros muelleri preferentially and quickly incorporated 13C into C18 PUFAs such as 18:2n-6 and 18:3n-6 as well as 16:0 and 16:1n-7, which were thus highly 13C-enriched. During the experiment, 20:5n-3 and 16:3n-4 were among the least-enriched fatty acids. The calculation of the enrichment percentage ratio of a fatty acid B over its suspected precursor A allowed us to suggest that the diatom produced 20:5n-3 (EPA) by a combination between the n-3 (via 18:4n-3) and n-6 (via 18:3n-6 and 20:4n-6) synthesis pathways as well as the alternative &omega, 3 desaturase pathway (via 20:4n-6). In addition, as FA from polar lipids were generally more enriched in 13C than FA from neutral lipids, particularly for 18:1n-9, 18:2n-6 and 18:3n-6, the existence of acyl-editing mechanisms and connectivity between polar and neutral lipid fatty acid pools were also hypothesized. Because 16:3n-4 and 20:5n-3 presented the same concentration and enrichment dynamics, a structural and metabolic link was proposed between these two PUFAs in C. muelleri.

Oysters are keystone species that use external fertilization as a sexual mode. The gametes are planktonic and face a wide range of stressors, including plastic litter. Nanoplastics are of increasing concern because their size allows pronounced interactions with biological membranes, making them a potential hazard to marine life. In the present study, oyster spermatozoa were exposed for 1 h to various doses (from 0.1 to 25 µg mL−1) of 50-nm polystyrene beads with amine (50-NH2 beads) or carboxyl (50-COOH beads) functions. Microscopy revealed adhesion of particles to the spermatozoa membranes, but no translocation of either particle type into cells. Nevertheless, the 50-NH2 beads at 10 µg mL−1 induced a high spermiotoxicity, characterized by a decrease in the percentage of motile spermatozoa (−79%) and in the velocity (−62%) compared to control spermatozoa, with an overall drop in embryogenesis success (−59%). This major reproduction failure could be linked to a homeostasis disruption in exposed spermatozoa. The 50-COOH beads hampered spermatozoa motility only when administered at 25 µg mL−1 and caused a decrease in the percentage of motile spermatozoa (−66%) and in the velocity (−38%), but did not affect embryogenesis success. Microscopy analyses indicated these effects were probably due to physical blockages by microscale aggregates formed by the 50-COOH beads in seawater. This toxicological study emphasizes that oyster spermatozoa are a useful and sensitive model for (i) deciphering the fine interactions underpinning nanoplastic toxicity and (ii) evaluating adverse effects of plastic nanoparticles on marine biota while waiting for their concentration to be known in the environment.

International audience; The dinoflagellate genus Alexandrium comprises species that produce highly potent neurotoxins known as paralytic shellfish toxins (PST), and bioactive extracellular compounds (BEC) of unknown structure and ecological significance. The toxic bloom-forming species, Alexandrium minutum, is distributed worldwide and adversely affects many bivalves including the commercially and ecologically important Pacific oyster, Crassostrea gigas. In France, recurrent A. minutum blooms can co-occur with C. gigas spawning and larval development, and may endanger recruitment and population renewal. The present study explores how A. minutum affects early-oyster development by exposing embryos and larvae, under controlled laboratory conditions, to two strains of A. minutum, producing only BEC or both PST and BEC. Results highlight the major role of BEC in A. minutum toxicity upon oyster development. The BEC strain caused lysis of embryos, the most sensitive stage to A. minutum toxicity among planktonic life-stages. In addition, the non-PST-producing A. minutum strain inhibited hatching, disrupted larval swimming behavior, feeding, growth, and induced drastic decreases in survival and settlement of umbonate and eyed larvae (9 and 68 %, respectively). The findings indicated PST accumulation in oyster larvae (e.g. umbonate stages), possibly impairing development and settlement of larvae in response to the PST-producing strain. This work provides evidences that A. minutum blooms could hamper settlement of shellfish.

International audience; Disseminated neoplasia (DN) is a disease that affects bivalves worldwide and can lead to mass mortalities. In the present study, a pathological survey conducted from December 2011 to August 2012 in Crassostrea gasar, an oyster of commercial interest in northeast Brazil, revealed the occurrence of DN in oysters reared in the Mamanguape estuary, Paraiba State, Brazil. The present work describes the pathological and functional aspects of the disease in C. gasar by light microscopy (haemolymph cell monolayer and histological section) and flow cytometry analyses. The prevalence of the disease was low (7.1% of 182 oysters examined). Enlarged (neoplastic) cells showed reniform, ovoid or circular-shaped nuclei, with prominent nucleoli and predominantly short filipodia. They were found in the haemolymph and infiltrated the connective tissues of different organs, including the digestive system, gills and gonads, as well as in the sinuses and vessels. Three levels of progression of DN in tissues were observed, light (61.5%), moderate (15.4%) and advanced (23.1%). The viability of neoplastic cells circulating in the haemolymph (97.4%) was similar to that in the haemocytes (95.7%). The neoplastic cells showed low phagocytic ability (3.9%) compared with that of haemocytes (42.4%). Conversely, reactive oxygen species production (679 A.U.) and the total haemocyte count (3.9 x 10(6) cells mL(-1)) were higher in the affected oysters than in unaffected oysters (268 A.U. and 1.5 x 10(6) cells mL(-1), respectively). The low prevalence and primarily mild intensity found in the sampled oysters does not preclude an impact at the population level. A timely survey of DN is thus recommended in order to assess the severity and impact of this disease in wild and cultured populations of C. gasar oysters.

International audience; Plastics are found to be major debris composing marine litter; microplastics (MP, < 5 mm) are found in all marine compartments. The amount of MPs tends to increase with decreasing size leading to a potential misidentification when only visual identification is performed. These last years, pyrolysis coupled with gas chromatography/mass spectrometry (Py-GC/MS) has been used to get information on the composition of polymers with some applications on MP identification. The purpose of this work was to optimize and then validate a Py-GC/MS method, determine limit of detection (LOD) for eight common polymers, and apply this method on environmental MP. Optimization on multiple GC parameters was carried out using polyethylene (PE) and polystyrene (PS) microspheres. The optimized Py-GC/MS method require a pyrolysis temperature of 700 °C, a split ratio of 5 and 300 °C as injector temperature. Performance assessment was accomplished by performing repeatability and intermediate precision tests and calculating limit of detection (LOD) for common polymers. LODs were all below 1 μg. For performance assessment, identification remains accurate despite a decrease in signal over time. A comparison between identifications performed with Raman micro spectroscopy and with Py-GC/MS was assessed. Finally, the optimized method was applied to environmental samples, including plastics isolated from sea water surface, beach sediments, and organisms collected in the marine environment. The present method is complementary to μ-Raman spectroscopy as Py-GC/MS identified pigment containing particles as plastic. Moreover, some fibers and all particles from sediment and sea surface were identified as plastic.

International audience; The lipid class and the fatty acid compositions of microalgae highly influence bivalve larval and post-larval development. Light is an essential environmental factor for microalgal culture, and quantity and quality of light may induce changes in the biochemical composition of the algae. The objective of this study was to investigate the effect of light spectrum (blue vs. white light) on lipid class and fatty acid compositions of Tisochrysis lutea cultured in a chemostat. Two different dilution rates (D) were assayed for each light spectrum: 0.2 and 0.7 day−1. Triacylglycerol (TAG), sterol, and hydrocarbon (HC) content increased sharply at low D. The proportion of alkenones was significantly reduced under blue light. Polyunsaturated fatty acids (PUFA), and particularly n-3 PUFA, content in phospholipids (PL) increased under blue light compared to white light at low D. Thus, blue light raised 22:6(n-3) levels in total lipids of T. lutea at low D. The cultivation of T. lutea in a chemostat at low D under blue light may improve nutritional value as feed for bivalve larvae by modifying the PUFA profile, especially increasing 22:6(n-3).

International audience; The 2010 explosion of the Deepwater Horizon (DWH) oil rig generated the largest marine oil spill in US history with millions of barrels of crude oil released in the Gulf of Mexico (GoM). The eastern oyster, Crassostrea virginica, is an ecologically and economically important species in the northern GoM. Due to its biological characteristics (sessile, filter feeding), juvenile oysters may have been affected. This study investigated the effects of surface-collected DWH oil prepared as high-energy water-accommodated fraction (HEWAF) on the survival of 2-month-old oyster spat, and evaluated the potential impacts of HEWAF on particle clearance rate and spat tissue. Exposure of oysters to a range of oil/HEWAF (0–7–66–147–908–3450 μg tPAH50 (sum of 50 polycyclic aromatic hydrocarbons) L−1) resulted in non-dose-dependent mortalities and reduced clearance rates of algal food (Tisochrysis lutea). A morphometric study of the digestive tubules (DGTs) indicated a dose-dependent response to oil exposure on lumen dilation, on epithelium thinning of the DGT, and a significant change in DGT synchrony (LOEC = 66 μg tPAH50 L−1). This finding suggests that structural changes occurred in the digestive gland of exposed oysters most likely due to an oil-related stress. In addition, histological observations showed that tissues in contact with HEWAF (gills, palp, connective tissue, digestive gland) were adversely impacted at ≥ 7 μg tPAH50 L−1, and exhibited pathological symptoms typical of an inflammatory response (e.g., hemocyte diapedesis and infiltration, syncytia, epithelium sloughing).

To understand the fate and impacts of microplastics (MP) in the marine ecosystems, it is essential to investigate their interactions with phytoplankton as these may affect MP bioavailability to marine organisms as well as their fate in the water column. However, the behaviour of MP with marine phytoplanktonic cells remains little studied and thus unpredictable. The present study assessed the potential for phytoplankton cells to form hetero-aggregates with small micro-polystyrene (micro-PS) particles depending on microalgal species and physiological status. A prymnesiophycea, Tisochrysis lutea, a dinoflagellate, Heterocapsa triquetra, and a diatom, Chaetoceros neogracile, were exposed to micro-PS (2 μm diameter; 3.96 μg L −1 ) during their growth culture cycles. Micro-PS were quantified using an innovative flow-cytometry approach, which allowed the monitoring of the micro-PS repartition in microalgal cultures and the distinction between free suspended micro-PS and hetero-aggregates of micro-PS and microalgae. Hetero-aggregation was observed for C. neogracile during the stationary growth phase. The highest levels of micro-PS were “lost” from solution, sticking to flasks, with T. lutea and H. triquetra cultures. This loss of micro-PS sticking to the flask walls increased with the age of the culture for both species. No effects of micro-PS were observed on microalgal physiology in terms of growth and chlorophyll fluorescence. Overall, these results highlight the potential for single phytoplankton cells and residual organic matter to interact with microplastics, and thus potentially influence their distribution and bioavailability in experimental systems and the water column.

International audience; The 2010 Deepwater Horizon (DWH) oil spill released millions of barrels of oil and dispersant into the Gulf of Mexico. The timing of the spill coincided with the spawning season of Crassostrea virginica. Consequently, gametes released in the water were likely exposed to oil and dispersant. This study aimed to (i) evaluate the cellular effects of acute exposure of spermatozoa and oocytes to surface slick oil, dispersed mechanically (HEWAF) and chemically (CEWAF), using flow-cytometric (FCM) analyses, and (ii) determine whether the observed cellular effects relate to impairments of fertilization and embryogenesis of gametes exposed to the same concentrations of CEWAF and HEWAF. Following a 30-min exposure, the number of spermatozoa and their viability were reduced due to a physical action of oil droplets (HEWAF) and a toxic action of CEWAF respectively. Additionally, reactive oxygen species (ROS) production in exposed oocytes tended to increase with increasing oil concentrations suggesting that exposure to dispersed oil resulted in an oxidative stress. The decrease in fertilization success (1-h), larval survival (24-h) and increase in abnormalities (6-h and 24-h) may be partly related to altered cellular characteristics. FCM assays are a good predictor of sublethal effects especially on fertilization success. These data suggest that oil/dispersant are cytotoxic to gametes, which may affect negatively the reproduction success and early development of oysters.

WOS:000533524300107; The impact of nanoplastics (NP) using model polystyrene nanoparticles amine functionalized (PS-NH2) has been investigated on pigment and lipid compositions of the marine diatom Chaetoceros neogracile, at two growth phases using a low (0.05 mu g mL(-1)) and a high (5 mu g mL(-1)) concentrations for 96 h. Results evidenced an impact on pigment composition associated to the light-harvesting function and photo-protection mainly at exponential phase. NP also impacted lipid composition of diatoms with a readjustment of lipid classes and fatty acids noteworthy. Main changes upon NP exposure were observed in galactolipids and triacylglycerol's at both growth phases affecting the thylakoids membrane structure and cellular energy reserve of diatoms. Particularly, exponential cultures exposed to high NP concentration showed an impairment of long chain fatty acids synthesis. Changes in pigment and lipid content of diatom' cells revealed that algae physiology is determinant in the way cells adjust their thylakoid membrane composition to cope with NP contamination stress. Compositions of reserve and membrane lipids are proposed as sensitive markers to assess the impact of NP exposure, including at potential predicted environmental doses, on marine organisms. (C) 2020 Elsevier Ltd. All rights reserved.

International audience; Due to the growing concern about the presence of microplastics (MP) in the environment, the number of studies evaluating the toxicity of these small persistent particles on different marine species has increased in recent years. Few studies have addressed their impact on marine phytoplankton, a subject of great concern since they are primary producers of the aquatic food web. The aim of this study is to unravel the cytotoxicity of 2.5 mu g mL(-1) unlabelled amino-modified polystyrene beads of different sizes (0.5 and 2 mu m) on the marine diatom Chaetoceros neogracile. In addition to traditional growth and photosynthesis endpoints, several physiological and biochemical parameters were monitored every 24 h in C. neogracile cells by flow cytometry during their exponential growth (72 h). Dynamic Light Scattering measurements revealed the strong aggregation and the negative charge of the beads assayed in the culture medium, which seemed to minimize particle interaction with cells and potentially associated impacts. Indeed, MP were not attached to the microalgal cell wall, as evidenced by scanning electron micrographs. Cell growth, morphology, photosynthesis, reactive oxygen species levels and membrane potential remained unaltered. However, exposure to MP significantly decreased the cellular esterase activity and the neutral lipid content. Microalgal oil bodies could serve as an energy source for maintaining a healthy cellular status. Thus, MP-exposed cells modulate their energy metabolism to properly acclimate to the stress conditions.

International audience; The potential presence of nanoplastics (NP) in aquatic environments represents a growing concern regarding their possible effects on aquatic organisms. The objective of this study was to assess the impact of polystyrene (PS) amino-modified particles (50 nm PSNH2) on the cellular and metabolic responses of the diatom Chaetoceros neogracile cultures at two essential phases of the growth cycle, i.e. exponential (division) and stationary (storage) phases. Both cultures were exposed for 4 days to low (0.05 μg mL−1) and high (5 μg mL−1) concentrations of PS-NH2. Exposure to NP impaired more drastically the major cellular and physiological parameters during exponential phase than during the stationary phase. Only an increase in ROS production was observed at both culture phases following NP exposures. In exponential phase cultures, large decreases in chlorophyll content, esterase activity, cellular growth and photosynthetic efficiency were recorded upon NP exposure, which could have consequences on the diatoms life cycle and higher food-web levels. The observed differential responses to NP exposure according to culture phase could reflect i) the higher concentration of Transparent Exopolymer Particles (TEP) at stationary phase leading to NP aggregation and thus, probably minimizing NP effects, and/or ii) the fact that dividing cells during exponential phase may be intrinsically more sensitive to stress. This work evidenced the importance of algae physiological state for assessing the NP impacts with interactions between NP and TEP being one key factor affecting the fate of NP in algal media and their impact to algal’ cells.; La présence potentielle de nanoplastiques (NP) dans les milieux aquatiques constitue une préoccupation croissante en ce qui concerne leurs éventuels effets sur les organismes aquatiques. L’objectif de cette étude était d’évaluer l’impact des particules de polystyrène (PS) amino-modifiées (50 nm PS [sbnd] NH2) sur les réponses cellulaires et métaboliques de la diatomée Chaetoceros néogracile dans les cultures à deux phases essentielles du cycle de croissance, c'est-à-dire des phases exponentielles (division) et stationnaires (stockage). Les deux cultures ont été exposées pendant 4 jours à des concentrations faibles (0,05 μg.mL-1) et élevées (5 μg.mL-1) de PS-NH2. L'exposition au NP a altéré plus fortement les principaux paramètres cellulaires et physiologiques au cours de la phase exponentielle par rapport à la phase stationnaire. Seule une augmentation de la production de ROS a été observée aux deux phases de la culture après l'exposition au NP. Dans les cultures en phase exponentielle, l'exposition au NP avait entraîné une diminution importante de la teneur en chlorophylle, de l'activité estérase, de la croissance cellulaire et de l'efficacité photosynthétique, ce qui pourrait avoir des conséquences sur le cycle de vie des diatomées et sur des niveaux plus élevés du réseau trophique. Les réponses différentielles observées à l'exposition au NP en fonction de la phase de culture pourraient refléter i) la concentration plus élevée de particules exopolymères transparentes (TEP) à la phase stationnaire conduisant à une agrégation de NP et donc, minimisant probablement les effets de NP, et / ou ii) le fait que les cellules en division pendant la phase exponentielle peut être intrinsèquement plus sensible au stress.

International audience; Plastic debris are classified as a function of their size and recently a new class was proposed, the nanoplastics. Nano-sized plastics have a much greater surface area to volume ratio than larger particles, which increases their reactivity in aquatic environment, making them potentially more toxic. Only little information is available about their behavior whereas it crucially influences their toxicity. Here, we used dynamic light scattering (DLS) to explore the influence of environmental factors (fresh- and saltwater, dissolved organic matter) on the behavior (surface charge and aggregation state) of three different nano-polystyrene beads (50 nm), with (i) no surface functionalization (plain), (ii) a carboxylic or (iii) an amine functionalization. Overall, the positive amine particles were very mildly affected by changes in environmental factors with no effect of the salinity gradient (from 0 to 653 mM) and of a range 1–30 μg.L−1 and 1–10 μg.L−1 of organic matter in artificial seawater and ultrapure water, respectively. These observations are supposedly linked to a coating specificity leading to repulsive mechanisms. In contrast, the stability of the negatively charged carboxylic and plain nanobeads was lost under an increasing ionic strength, resulting in homo-aggregation (up to 10 μm). The increase in organic matter content had negligible effect on these two nanobeads. Analysis performed over several days demonstrated that nanoplastics formed evolving dynamic structures detected mainly with an increase of the homo-aggregation level. Thus, surface properties of given polymers/particles are expected to influence their fate in complex and dynamic aquatic environments.

International audience; The dinoflagellate Alexandrium minutum produces toxic compounds, including paralytic shellfish toxins, but also some unknown extracellular toxins. Although copper (Cu) is an essential element, it can impair microalgal physiology and increase their toxic potency. This study investigated the effect of different concentrations of dissolved Cu (7 nM, 79 nM and 164 nM) on A. minutum allelochemical potency, here defined as negative effects of a protist on competing protists through the release of chemicals. This was studied in relation to its physiology. The effects of Cu were assessed on A. minutum growth, reactive oxygen species level, photosynthesis proxies, lipid metabolism, exudation of dissolved organic compounds, allelochemical potency and on the associate free bacterial community of A. minutum. Only the highest Cu exposure (164 nM) inhibited and delayed the growth of A. minutum, and only in this treatment did the allelochemical potency significantly increase, when the dissolved Cu concentration was still toxic. Within the first 7 days of the high Cu treatment, the physiology of A. minutum was severely impaired with decreased growth and photosynthesis, and increased stress responses and free bacterial density per algal cell. After 15 days, A. minutum partially recovered from Cu stress as highlighted by the growth rate, reactive oxygen species level and photosystem II yields. This recovery could be attributed to the apparent decrease in background dissolved Cu concentration to a non-toxic level, suggesting that the release of exudates may have partially decreased the bioavailable Cu fraction. Overall, A. minutum appeared quite tolerant to Cu, and this work suggests that the modifications in the physiology and in the exudates help the algae to cope with Cu exposure. Moreover, this study shows the complex interplay between abiotic and biotic factors that can influence the dynamic of A. minutum blooms. Modulation in allelochemical potency of A. minutum by Cu may have ecological implications with an increased competitiveness of this species in environments contaminated with Cu.

Hydrogen isotope ratios of biomarkers have been shown to reflect water isotope ratios, and in some cases correlate significantly with salinity. The δ2H-salinity relationship is best studied for long-chain alkenones, biomarkers for haptophyte algae, and is known to be influenced by a number of different environmental parameters. It is not fully known why δ2H ratios of lipids retain a correlation to salinity, and whether this is a general feature for other lipids produced by haptophyte algae. Here, we analyzed δ2H ratios of three fatty acids, brassicasterol, long-chain C37 alkenones and phytol from three different haptophyte species grown over a range of salinities. Lipids synthesized in the cytosol, or relying on precursors of cytosolic origin, show a correlation between their δ2H ratios and salinity. In contrast, biosynthesis in the chloroplast, or utilizing precursors created in the chloroplast, yields lipids that do not show a correlation between δ2H ratios and salinity. This leads to the conclusion that location of metabolism is the first-order control on the salinity signal retained in δ2H ratios of certain lipids. Additionally, we found that δ2H ratios of alkenones from batch cultures of the Group II haptophyte species Tisochrysis lutea correlate positively with temperature, contrary to findings from cultures of Group III haptophytes, but retain a similar response to nutrient availability in line with other Group III haptophytes.

International audience; Harmful algal blooms are a threat to aquatic organisms and coastal ecosystems. Among harmful species, the widespread distributed genus Alexandrium is of global importance. This genus is well-known for the synthesis of paralytic shellfish toxins which are toxic for humans through the consumption of contaminated shellfish. While the effects of Alexandrium species upon the physiology of bivalves are now well documented, consequences on reproduction remain poorly studied. In France, Alexandrium minutum blooms have been recurrent for the last decades, generally appearing during the reproduction season of most bivalves including the oyster Crassostrea gigas. These blooms could not only affect gametogenesis but also spawning, larval development or juvenile recruitment. This study assesses the effect of toxic A. minutum blooms on C gigas reproduction. Adult oysters were experimentally exposed to A. minutum, at environmentally realistic concentrations (10(2) to 10(3) cells mL(-1)) for two months during their gametogenesis and a control group, not exposed to A. minutum was fed with a non-toxic dinoflagellate. To determine both consequences to next generation and direct effects of A. minutum exposure on larvae, the embryo-larval development of subsequent offspring was conducted with and without A. minutum exposure at 10(2) cells mL(-1). Effects at each stage of the reproduction were investigated on ecophysiological parameters, cellular responses, and offspring development. Broodstock exposed to A. minutum produced spermatozoa with decreased motility and larvae of smaller size which showed higher mortalities during settlement. Embryo-larval exposure to A. minutum significantly reduced growth and settlement of larvae compared to non-exposed offspring. This detrimental consequence on larval growth was stronger in larvae derived from control parents compared to offspring from exposed parents. This study provides evidence that A. minutum blooms, whether they occur during gametogenesis, spawning or larval development, can either affect gamete quality and/or larval development of C gigas, thus potentially impacting oyster recruitment.

International audience; Nowadays, environmental pollution by microplastics (