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Eight different experimental substrates were tested on Paracentrotus lividus competent larvae in order to evaluate their potential for inducing metamorphosis and enhance survival after recruitment. Two benthic diatoms species, Nitzschia laevis (NL) and Halamphora coffeaeformis (HC), were selected according to their capacity to adhere and to form strong biofilms. They were tested in monocultures and in a mixed biofilm (MIX) that was also tried in combination with Gamma-Aminobutyric Acid, involved in triggering some invertebrate metamorphosis (MIX + GABA). Histamine (HIS) was also used as a treatment according to the high metamorphosis rates that have been recorded for this compound on other sea urchin species. Finally, a natural microphytobenthic biofilm (NATURAL) and oyster shells particles colonized by epiphytic diatoms (SHELL) were sampled from the mud of a refining oyster pond. Batches of 21 days-old larvae were placed on each experimental substrate and their effect was compared to a negative control of filtered sea water (without any treatment; FSW). Metamorphosis rate was daily recorded in each treatment. The sea urchin larvae on substrates NL, NATURAL, GABA + MIX and SHELL showed significantly higher metamorphosis rates than larvae on the other treatments (P

International audience; The aim of the present study was to evaluate the presence and potential toxic effects of plastic fragments (< 400 μm) of polyethylene and polypropylene on the Pacific oyster Crassostrea gigas. Oysters were exposed to environmentally relevant concentrations (0, 0.008, 10, 100 μg of particles/L) during 10 days, followed by a depuration period of 10 days in clean seawater. Effects of microplastics were evaluated on the clearance rate of organisms, tissue alteration, antioxidant defense, immune alteration and DNA damage. Detection and quanti-fication of microplastics in oyster's tissues (digestive gland, gills and other tissues) and biodeposits using infrared microscopy were also conducted. Microplastics were detected in oyster's biodeposits following exposure to all tested concentrations: 0.003, 0.006 and 0.05 particles/mg of biodeposits in oysters exposed to 0.008, 10 and 100 μg of particles/L, respectively. No significant modulation of biological markers was measured in organisms exposed to microplastics in environmentally relevant conditions.

Haslea ostrearia is a marine diatom that synthesizes and releases marennine, a water-soluble blue-green pigment responsible for the greening of the gills and labial palps of bivalves. The present study evaluated the effect of different marennine concentrations (0, 0.5, 1.0 and 2.0 mg l− 1) on the behavior (valve opening), physiology (clearance rates, oxygen consumption, assimilation efficiency and scope for growth) and biochemistry (fatty acid composition of neutral and polar lipids) of two commercially important bivalves, the blue mussel Mytilus edulis and the eastern oyster Crassostrea virginica. Under short-term (

The impact of a microplastic (MP) mixture composed of polyethylene (PE) and polypropylene (PP) plastic particles, prepared from commercially available products, was evaluated in blue mussels Mytilus spp. exposed to three environmentally relevant concentrations: 0.008 μg L−1 (low), 10 μg L−1 (medium), and 100 μg L−1 (high). Organisms were exposed for 10 days followed by 10 days of depuration in clean seawater under controlled laboratory conditions. The evaluation of MP effects on mussel clearance rate, tissue structure, antioxidant defenses, immune and digestive parameters, and DNA integrity were investigated while the identification of plastic particles in mussel tissues (gills, digestive gland, and remaining tissues), and biodeposits (feces and pseudofaeces) was performed using infrared microscopy (μFT-IR). Results showed the presence of MPs only in the digestive gland of mussels exposed to the highest tested concentration of MPs with a mean of 0.75 particle/mussel (after the 10 days of exposure). In biodeposits, PE and PP particles were detected following exposure to all tested concentrations confirming the ingestion of MPs by the organisms. A differential response of antioxidant enzyme activities between digestive gland and gills was observed. Significant increases in superoxide dismutase (SOD) and catalase (CAT) activities were measured in the digestive gland of mussels exposed to the low (0.008 μg L−1) and medium (10 μg L−1) concentrations of MPs and in the gills from mussels exposed to the highest concentration (100 μg L−1) of MPs that could be indicative of a change in the redox balance. Moreover, an increase in acid phosphatase activity was measured in hemolymph of mussels exposed to 0.008 and 10 μg L−1 concentrations. No significant difference was observed in the clearance rate, and histopathological parameters between control and exposed mussels. This study brings new insights on the potential sublethal impacts of MPs at environmentally relevant concentrations in marine bivalves.

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARE [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; Trophic ecology is the study of feeding interactions and food acquisition by organisms. It includes the causes and consequences of those behaviours at all levels of biological organisation. As a field of research, it crosses many disciplinary boundaries and provides knowledge that is pertinent to many other areas of ecology. Here we list and categorise the methods available to trophic ecologists whose toolbox has broadened considerably in recent years. They encompass empirical and numerical approaches with focus ranging from molecules to ecosystems. We further examine the relationship of each method to features such as the scale of observation (from microbes to largest organisms) and organisational level (from individuals to ecosystems) as well as the ecological question the method is capable of answering (from detecting predator-prey relationships to studying implications and consequences at different scales). Our survey reveals a very wide range of methodologies, each more-or-less appropriate for a particular line of research. It also identifies deficits, for example, trophic interactions at microscopic scales, for which empirical methods have hardly been used, as well as trophic models that have failed to consider fluxes at the ecosystem scale. Furthermore, we note that the combination of methodologies remains under-exploited despite great opportunities to solve complex ecological questions and to foster the emergence of new insights and hypotheses regarding organism, population and/or ecosystem properties.

Haslea ostrearia is a marine diatom known to produce marennine, a water-soluble blue-green pigment responsible for the greening of oysters in ponds along the French Atlantic coast. This phenomenon occurs seasonally when H. ostrearia blooms in oyster ponds, and it increases the economic value of cultured oysters. From an ecological perspective, H. ostrearia blooms are accompanied by a decrease in the abundance of other microalgae, suggesting that this diatom produces allelochemicals. Recent studies showed that purified marennine has other biological activities, for instance antioxidant, antibacterial, and antiviral activities, which could be used in aquaculture to promote this pigment as a natural antipathogen agent. One important issue regarding the possible use of H. ostrearia in aquaculture as a mixed algal diet, however, is the importance of marennine allelopathy. In this study, we investigated the allelopathic effect of H. ostrearia on the growth of five microalgal species relevant to aquaculture: Chaetoceros calcitrans, Skeletonema costatum, Phaeodactylum tricornutum, Tetraselmis suecica, and Tisochrysis lutea. Allelopathic tests were realized by co-culturing these microalgae with H. ostrearia in batch and in semi-continuous mode, based on initial biovolume ratios. Our findings showed that inhibition of the growth of microalgae due to the presence of H. ostrearia and marennine was species dependent. Skeletonema costatum, C. calcitrans, and T. lutea were significantly more sensitive, whereas T. suecica and P. tricornutum appeared to be more resistant. Growth irradiance significantly influenced the allelopathic effect against the sensitive species S. costatum, and the H. ostrearia production of marennine increases with irradiance. Data presented in this study partly support the hypothesis that marennine released into the culture medium possibly acts as an allelochemical compound, thus explaining the dominance of H. ostrearia and the loss of sensitive algae in oyster ponds, but also that some species are insensitive, which allows co-culturing and use in a mixed algal diet in aquaculture.

The suitability of two red algae species, the introduced Grateloupia turuturu and the native Palmaria palmata, as feed for the culture of the European abalone Haliotis tuberculata, was compared over a 5-month period. Three experimental diets were tested: (1) P. palmata, (2) G. turuturu, and (3) a mixed diet of P. palmata and G. turuturu (1:1). Biochemical composition (proteins, carbohydrates, lipids, ashes) of algae was measured. No mortality was observed during the time of the experiment in any of the treatments. Growth in length and weight was higher for abalone fed with P. palmata and the mixed diet. Abalone exhibited a preference for P. palmata and showed the highest weight gain with this macroalgae (107.8 ± 7.2 %). Grateloupia turuturu disintegrated faster in abalone rearing conditions and was not suitable for significant growth of H. tuberculata in a monospecific diet. However, when it is provided in a mixed diet, abalone seem to show a higher lipid content than when fed a P. palmata monospecific diet. The invasive G. turuturu could be an interesting food supplement for European abalone.

The objective of this study was to optimise the rearing of the sea urchin Paracentrotus lividus (Lamarck, 1816) larvae through the choice of an optimal diet. The effects on larvae reared in oyster facilities and using different microalgae species were analysed. Four experimental diets were tested: 1) Isochrysis aff. galbana (Clone T-ISO), 2) Dunaliella tertiolecta, 3) Rhodomonas sp. and 4) a combined diet of these three species (1:1:1). The biometrics of larvae were carried out every two days. Post-larval survival was assessed when competence for settlement was achieved. Induction of settlement was carried out by contact between larvae and oyster shell particles. This method, adapted from oyster farming, was used for the first time in sea urchin culture. After 9 days post-settlement, metamorphosed juveniles were sampled and post-settlement survival was assessed. The biochemical composition (proteins, carbohydrates, lipids) of microalgae and larvae was measured. Age at competence was reached at 15 days post-fertilisation for all diets. Larval survival rate and growth in length and width were higher for larvae fed with Rhodomonas sp. These larvae also had the highest lipid content. Post-settlement survival was higher in larvae fed with the combined diet. Larvae in all treatments demonstrated normal growth and development, but Rhodomonas sp. presented nutritional advantages for sea urchin larvae: a more rapid development and a higher lipid content. The use of Rhodomonas sp., already widely used in oyster aquaculture, as a diet in Paracentrotus lividus culture could be a factor in enabling oyster farmers to diversify towards “echinoculture” and increase their revenue.

Satellite remote sensing (RS) is routinely used for the large-scale monitoring of microphytobenthos (MPB) biomass in intertidal mudflats, and has greatly improved our knowledge of MPB spatio-temporal variability and its potential drivers. Processes operating at smaller scales however, such as the impact of benthic macrofauna on MPB development, to date remain underinvestigated. In this study, we analysed the influence of wild Crassostrea gigas oyster reefs on MPB biofilm development using multispectral RS. A 30-year time series (1985–2015) combining high resolution (30 m) Landsat and SPOT data was built in order to explore the relationship between C. gigas reefs and MPB spatial distribution and seasonal dynamics, using the normalized difference vegetation index (NDVI). Emphasis was placed on the analysis of a before after control impact (BACI) experiment designed to assess the effect of oyster killing on the surrounding MPB biofilms. Our RS data reveal that the presence of oyster reefs positively affects MPB biofilm development. Analysis of the historical time series first showed the presence of persistent, highly concentrated MPB patches around oyster reefs. This observation was then confirmed by the BACI experiment which showed that killing the oysters (while leaving the physical reef structure, i.e. oyster shells, intact) negatively affected both MPB biofilm biomass and spatial stability around the reef. As such, our results are consistent with the hypothesis of nutrient input as an explanation for the MPB growth promoting effect of oysters, whereby organic and inorganic matter released through oyster excretion and biodeposition stimulates MPB biomass accumulation. MPB also showed marked seasonal variations in biomass and patch shape, size and degree of aggregation around the oyster reefs. Seasonal variations in biomass, with higher NDVI during spring and fall, were consistent with those observed at broader scales in other European mudflats. Our study provides the first multi-sensor RS satellite evidence of the promoting and structuring effect of oyster reefs on MPB biofilms.

International audience; Metamorphosis induction cues (by chemical mediation or direct contact) were tested in Paracentrotus lividus using three different macroalgae treatments: Corallina sp., Palmaria palmata, and Laminaria digitata. Higher percentages of metamorphosis were reached in Paracentrotus lividus larvae by direct contact with a Palmaria palmata substrate.

COSELMAR, a 4-year project financed by the Région des Pays de la Loire at 2.1 M€, officially started on the 7th January 2013. The project is coordinated by Philipp Hess (IFREMER) and Sophie Pardo (Université de Nantes-LEMNA) and falls under the Federation for Research Institut Universitaire Mer et Littoral (IUML, FR CNRS 3473)*. COSELMAR has also been approved by the Scientific Council of the MSH Ange Guépin. COSELMAR is a research project uniting 5 research units of IFREMER and 11 laboratories of the Université de Nantes, along with academic partners, and national and international industries. The aim is to achieve a better understanding of the marine and coastal ecosystems and the associated resources. The project will also provide insights into risk management and prevention of natural events and anthropogenic impacts. COSELMAR’s main objective is to integrate and promote the interdisciplinary scientific work concerning the issues above in order to build a real expertise on potential risks of coastal and marine zones. The project is divided into 3 axes of research and 1 integrated axis, Le projet COSELMAR, financé par la Région des Pays de la Loire à hauteur de 2.1 M€ pour une durée de 4 ans, a commencé officiellement le 07 janvier 2013. Coordonné par Philipp Hess (IFREMER) et Sophie Pardo (Université de Nantes-LEMNA), il est un projet fédérateur pour la Fédération de Recherche Institut Universitaire Mer et Littoral (IUML, FR CNRS 3473)*. COSELMAR a également été agréé par le Conseil Scientifique de la MSH Ange Guépin. Cinq unités de recherches de l’IFREMER et onze laboratoires de l’Université de Nantes, appuyés par des partenariats académiques et industriels français et internationaux vont collaborer afin d'apporter une meilleure compréhension des écosystèmes littoraux et marins et des ressources associées, ainsi qu'une réflexion sur la gestion et la prévention des risques engendrés par les facteurs naturels et anthropiques. L'objectif principal de COSELMAR est d'intégrer des travaux scientifiques interdisciplinaires autour de ces questions afin de construire une véritable expertise sur les risques en milieu littoral et marin. Ce projet est divisé en trois axes de recherche et un axe intégrateur

The invasion of the wild oyster Crassostrea gigas along the western European Atlantic coast has generated changes in the structure and functioning of intertidal ecosystems. Considered as an invasive species and a trophic competitor of the cultivated conspecific oyster, it is now seen as a resource by oyster farmers following recurrent mass summer mortalities of oyster spat since 2008. Spatial distribution maps of wild oyster reefs are required by local authorities to help define management strategies. In this work, visible-near infrared (VNIR) hyperspectral and multispectral remote sensing was investigated to map two contrasted intertidal reef structures: clusters of vertical oysters building three-dimensional dense reefs in muddy areas and oysters growing horizontally creating large flat reefs in rocky areas. A spectral library, collected in situ for various conditions with an ASD spectroradiometer, was used to run Spectral Angle Mapper classifications on airborne data obtained with an HySpex sensor (160 spectral bands) and SPOT satellite HRG multispectral data (3 spectral bands). With HySpex spectral/spatial resolution, horizontal oysters in the rocky area were correctly classified but the detection was less efficient for vertical oysters in muddy areas. Poor results were obtained with the multispectral image and from spatially or spectrally degraded HySpex data, it was clear that the spectral resolution was more important than the spatial resolution. In fact, there was a systematic mud deposition on shells of vertical oyster reefs explaining the misclassification of 30% of pixels recognized as mud or microphytobenthos. Spatial distribution maps of oyster reefs were coupled with in situ biomass measurements to illustrate the interest of a remote sensing product to provide stock estimations of wild oyster reefs to be exploited by oyster producers. This work highlights the interest of developing remote sensing techniques for aquaculture applications in coastal areas.

Intertidal mudflats are important feeding areas for migrating and wintering shorebird species. Partial release of organic and inorganic nutrients through bird excretion may enrich the nutrients flow of mudflat ecosystems, especially in areas with a low flushing rate. The objective of the present work was to experimentally evaluate the effect of Dunlin droppings on the growth and biochemical composition of the microphytobenthic diatom, Entomoneis paludosa (W. Smith) Reimer. Different nutritional conditions were tested to investigate the impact on E. paludosa growth rate, biomass, elemental (CHN) and biochemical composition (lipids, proteins, carbohydrates, pigments). Various culture media were used going from plain artificial seawater to F/2 culture media containing variable nitrate concentrations (0; 50 or 882 μM-NO3) to which bird dropping extract was added or not. The faeces extracts contained inorganic nitrogen (9.1 μM-NH4), inorganic phosphorus (8.2 μM-PO4), traces of silicate (0.2 μM-Si), organic nitrogen in the form of urea (16 μM-N) and other dissolved organic nitrogen (120 μM-N). Faeces extract inartificial seawater was sufficient to sustain E. paludosa growth (up to 6.8 cell divisions in 9 days). A significant growth rate increase (+ 20%) and higher biomasses were observed when faeces extract was added to inorganic media enriched with 50 μM-NO3. Bird droppings had a significant effect in E. paludosa final biochemical composition with the addition of faeces extract to a culture medium containing 50 μM-NO3 increasing E. paludosa protein content and decreasing carbohydrate content. Pigment content per cell increased with the addition of bird dropping extract but ratios of light-harvesting and photo-protective pigments to chlorophyll a were unaffected. E. paludosa grown with faeces extract showed high cellular nitrogen and carbon contents, close to those obtained when cells were grown in F/2 medium. This study showed that shorebird droppings, through the addition of dissolved material, can significantly affect microphytobenthic diatom growth and biochemical composition.

International audience; The small-scale spatial distribution of Dunlin Calidris alpina staging and wintering in Bourgneuf Bay (France) was investigated on two different mudflats colonized by either epipsammic- or epipelic-dominated microphytobenthos assemblages. Shorebird counts were conducted monthly at ebb tide from October 2011 to May 2012 and from November 2012 to May 2013. Multiple linear regressions followed by hierarchical partitioning of variance showed that microphytobenthos biomass was not a significant factor to explain Dunlin densities. However, on epipelic-dominated mudflats, Dunlins did not show their typical ‘‘tide follower’’ behaviour and instead significantly selected the highest microphytobenthos biomass zones. The biomass of a gastropod predator of an important local Dunlin prey, Retusa obtusa, was negatively correlated with Dunlin densities. This paper provides new suggestions in the ways that biofilms on mudflats affect small shorebird foraging.