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International audience; Studies on phytoplankton and in particular Harmful Algal Blooms (HABs) species in southern Mediterranean waters are scarce. We performed from April 2008 to June 2009 weekly investigations on microphytoplankton community structure and abundance in two contrasted marine ecosystems located in the western Moroccan Mediterranean coast, M'diq Bay and Oued Laou Estuary. Simultaneously, we measured the main physico-chemical parameters. Globally, the two studied areas showed comparable values of the assessed abiotic environmental factors. Temperature and salinity followed seasonal variation with values ranging from 13.5°C to 21.4°C and 31 to 36.8, respectively. Average nutrient values in surface water ranged from 0.7 to 45.76 μM for dissolved inorganic nitrogen, 0.02-2.10 μM for PO 4 and 0.23-17.46 μM for SiO 4 in the study areas. A total of 92 taxa belonging to 8 taxonomic classes were found. The highest number of microphytoplankton abundance reached 1.2 × 10 6 cells L −1 with diatoms being the most abundant taxa. Factorial Discriminant Analysis (FDA) and Spearman correlation test showed a significant seasonal discrimination of dominant microphytoplankton species. These microorganisms were associated with different environmental variables, in particular temperature and salinity. Numerous HABs species were encountered regularly along the year. Although Dinophysis species and Prorocentrum lima were present in both sites, no Lipophilic Shellfish Poisoning was detected for the analyzed bivalve mollusks. Domoic acid (DA), produced by toxic species of Pseudo-nitzschia was found with concentrations up to 18 µg DA g −1 in the smooth clam Callista chione. Data showed that the observed persistent and dramatic Paralytic Shellfish Poisoning (PSP) intoxication of mollusks resulted probably of Gymnodinium catenatum pro-liferations in both studied areas. Contrary to C. chione, the cockle Achanthocardia tuberculatum showed a permanent and extremely high toxicity level during the 15 months survey with up to 7545 µg Equivalent Saxitoxin kg −1 flesh (ten times higher than the sanitary threshold of 800 µg eqSTX Kg −1 flesh). The present work highlights for the first time the dynamic of microphytoplankton including HABs species and their associated toxin accumulation in the commercially exploited shellfish in the southern western Mediterranean waters of Morocco. Furthermore, the acquired data will help us to improve the monitoring of HABs species and related toxins in these coastal marine systems.

International audience; Atoll lagoons display a high diversity of trophic states due mainly to their specific geomorphology, and probably to their level and mode of human exploitation. We investigated the functioning of the Ahe atoll lagoon, utilized for pearl oyster farming, through estimations of photosynthetic parameters (pulse amplitude modulation fluorometry) and primary production (13C incorporation) measurements of the size structured phytoplankton biomass (2 μm). Spatial and temporal scales of variability were surveyed during four seasons, over 16 months, at four sites within the lagoon. While primary production (P) was dominated by the picophytoplankton, its biomass specific primary productivity (PB) was lower than in other atoll lagoons. The variables size fraction of the phytoplankton, water temperature, season, the interaction term station * fraction and site, explained significantly the variance of the data set using redundancy analysis. No significant trends over depth were observed in the range of 0-20 m. A clear spatial pattern was found which was persistent over the seasons: south and north sites were different from the two central stations for most of the measured variables. This pattern could possibly be explained by the existence of water cells showing different water residence time within the lagoon. Photoacclimation strategies of the two size fractions differed through their light saturation coefficient (higher for picophytoplankton), but not through their maximum photosynthetic capacity (ETRmax). Positive linear relationships between photosynthetic parameters indicated that their dynamic was independent of light availability in this ecosystem, but most probably dependent on nutrient availability and/or rapid changes in the community structure. Spatial and temporal patterns of the measured processes are then further discussed in the context of nutrient availability and the possible role of cultured oysters in nutrient recycling

FR2116; International audience; From May 2002 to October 2003, a fortnightly sampling programme was conducted in a restricted macrotidal ecosystem in the English Channel, the Baie des Veys (France). Three sets of data were obtained: (1) physico-chemical parameters, (2) phytoplankton community structure illustrated by species composition, biovolume and diversity, and (3) primary production and photosynthetic parameters via P versus E curves. The aim of this study was to investigate the temporal variations of primary production and photosynthetic parameters in this bay and to highlight the potential links with phytoplankton community structure. The highest level of daily depth-integrated primary production Pz (0.02–1.43 g C m–2 d–1) and the highest maximum photosynthetic rate PB max (0.39– 8.48 mg C mg chl a–1 h–1) and maximum light utilization coefficient aB [0.002–0.119 mg C mg chl a–1 h–1(lmol photons m–2 s–1)] were measured from July to September. Species succession was determined based on biomass data obtained from cell density and biovolume measurements. The bay was dominated by 11 diatoms throughout the year. However, a Phaeocystis globosa bloom (up to 25 mg chl a m–3, 2.5 · 106 cells l–1) was observed each year during the spring diatom bloom, but timing and intensity varied interannually. Annual variation of primary production was due to nutrient limitation, light climate and water temperature. The seasonal pattern of microalgal succession, with regular changes in composition, biovolume and diversity, influenced the physico-chemical and biological characteristics of the environment (especially nutrient stocks in the bay) and thus primary production. Consequently, investigation of phytoplankton community structure is important for developing the understanding of ecosystem functioning, as it plays a major role in the dynamics of primary production.

Coccolithus braarudii and Calcidiscus leptoporus are 2 coccolithophores (Prymnesio- phyceae: Haptophyta) known to possess a complex heteromorphic life cycle, with alternation between a motile holococcolith-bearing haploid stage and a non-motile heterococcolith-bearing diploid stage. The ecological implications of this type of life cycle in coccolithophores are currently poorly known. The nutritional preferences of each stage of both species, and their growth response to conditions of turbulence were investigated by varying their growth conditions. Of the different cul- ture media tested, only the synthetic seawater medium did not support the growth of both stages of C. braarudii and C. leptoporus. With natural seawater-based media, the growth rate of the haploid phase of both coccolithophores was stimulated by the addition of soil extract (K/2: 0.23 ± 0.02 d -1 and K/2 with soil extract 0.35 ± 0.01 d -1 for the C. braarudii haploid stage), while the diploid phase was not, indicating that the motile stage is capable of utilizing compounds present in soil extract or ingest- ing bacteria that are activated in enriched media. The addition of sodium acetate to the medium also stimulated the haploid phase of C. braarudii, and further experiments using labeled bacteria demon- strated the capacity for phagotrophy of this motile stage. The effect of nutrient concentrations on the growth rates of both species was evaluated, showing clear differences between the 2 phases of the life cycle, with higher growth rates for the diploid stage in nutrient-rich media (K/2: 0.34 ± 0.04 d -1 , K/25: 0.29 ± 0.01 d -1 , K/100: 0.16 ± 0.01 d -1 for the haploid stage of C. leptoporus). Responses of the 2 phases of both coccolithophores to physical turbulence were also different, with a haploid flagellate stage sensitive to mixing and a more resistant non-motile diploid stage. The results of these experi- ments strongly indicate that each morphological stage of C. braarudii and C. leptoporus corresponds to a different ecological niche, the motile haploid stage exploiting a more stable oligotrophic niche than the diploid non-motile stage, in accordance with field observations. The 2-dimensional phyto- plankton niche space model of Margalef (1978; Oceanol Acta 1:493-509), defined by nutrients and turbulence, was amended to integrate this hypothesis.

The number of microalgae of high nutritional value actually available to mollusc hatcheries is limited to a few species and this represents a constraint for the industry. Fifteen microalgal species belonging to seven different taxonomic classes were selected from the Algobank-Caen microalgal culture collection of the University of Caen. An initial screening of these microalgae, based on their cytomorphological characteristics and growth performances, led to the selection of four species (Imantonia rotunda, Emiliania huxleyi, Pseudoisochrysis paradoxa and Diacronema vlkianum), which were then tested as food for Crassostrea gigas larvae. Two species (I. rotunda and E. huxleyi) were of poor food value for oyster larvae, while P. paradoxa and D. vlkianum resulted in high growth rate and low mortality. These two microalgae were then characterised (dry weight, ash, gross composition, fatty acids) at different stages of growth and their productivity in standard hatchery conditions (2-l glass carboys, 300-l cylinders) was assessed in order to evaluate the potential of these species for use in commercial hatcheries.

We studied the cryopreservation of the most common coccolithophore, Emiliania huxleyi which is considered as one of the main global carbon cycle participants. Both stages of this complex life cycle species were submitted to gradual addition of three distinct cryoprotectants: dimethylsulfoxide (7.5% v/v), methanol (5% v/v) and proline (0.5 M). They were then control-rate cooled (−5 °C min−1) to −50 °C before plunging into liquid nitrogen. Free radical oxygen species have been proposed to occur in cells subjected to pre-freezing manipulation or to cooling. Therefore, catalase (preventing accumulation of hydroxyl radicals) was evaluated for its ability to improve cell viability before and after freezing-thawing challenge.

Employment of heterotrophic culture of microalgal foods in the hatchery-based seed production of oysters is still controversial because some algae produced using the method appear to loose sterols, a key nutritional factor for bivalve growth. We traced the changes in sterol content of Tetraselmis suecica growing under photoautotrophic and heterotrophic conditions with the aid of gas chromatography (GC) and GC-mass spectrometry. The photoautotrophic T. suecica at the mid-logarithmic growth phase contained six major (cholesta-5,22-dien-3β-ol, ergost-5-en-3β-ol, cholest-5-en-3β-ol, 24-methylcholesta-5,22-dien-3β-ol, 24-methylcholesta-5,24-dien-3β-ol, and 24-ethylchlolesta-5,24-dien-3β-ol) and two minor sterols (24-methylcholesta-5-en-3β-ol and 24-ethylchlolesta-5en-3β-ol). In the comparison of algal growth and sterol level, photoautotrophic alga appeared to need higher amounts of major sterols for cell growth over heterotrophic alga. These findings, that heterotrophic alga needed less amount of sterols for growth, may have significant implications in the introduction of the method in bivalve hatcheries. We also reviewed the sterolic properties of the alga obtained from heterotrophic method with respect to bivalve aquaculture.

Phytoplankton live in fluctuating environments where many factors such as grazing pressure, sinking, light availability, nutrient uptake and turnover influence the distribution of phytoplankton in time and space. The purpose of this study was to investigate if under conditions of depletion of inorganic nitrogen, as recorded in summer in naturals waters, phytoplanktonic species have the capability of using organic nitrogen sources, including free or combined amino acids, in addition to inorganic nitrogen. The study has focussed on histidine, the degradation of which yielding potentially three nitrogen atoms for each molecule of histidine. Chlamydomonas reinhardtii (CCAP 11/32A) was cultivated axenically with two different sources of nitrogen (histidine and/or ammonium). In the presence of histidine as sole source of nitrogen, cell growth was comparable to that observed with the same concentration of nitrogen in ammonium form. In the presence of both histidine and ammonium, histidine degradation was observed only when the concentration of ammonium was depleted. Under these conditions, the first two enzymes of histidine degradation pathway, histidase (EC 4.3.1.3) and urocanase (EC 4.2.1.49) were produced and were co-ordinately regulated. Histidase activity was also controlled by succinate and glutamate as carbon sources. Histidase was purified 1018-fold and partially characterized. The molecular weight of the native enzyme was estimated to 152.4 kDa corresponding to four subunits of 38.1 kDa. The enzyme did not exhibit classical Michaelis-Menten kinetics but showed a relationship between the rate of catalysis (V) and the concentration of substrate (S), characteristic of negative allosteric behavior. A Hill coefficient of 4 was measured for histidine concentrations higher than 20.5 mM.

The antifouling activity of extracts (aqueous, ethanol, and dichloromethane) of 9 marine macroalgae against bacteria, fungi, diatoms, macroalgal spores, mussel phenoloxidase activity, and barnacle cypris larvae has been investigated in relation to season in bimonthly samples from the Bay of Concarneau (France). Of the extracts tested, 48.2% were active against at least one of the fouling organisms, and of these extracts, 31.2% were seasonally active with a peak of activity in summer corresponding to maximal values for water temperature, light intensity, and fouling pressure, and 17% were active throughout the year. This seasonal activity may be adaptive as it coincides with maximal fouling pressure in the Bay of Concarneau. Dichloromethane extracts of Rhodophyceae were the most active in the antifouling assays.

Variations in the HPLC-derived pigment composition of cultured Pavlovophyceae (Cavalier-Smith) Green et Medlin were compared with phylogenetic relationships inferred from 18S rDNA sequencing, morphological characteristics, and current taxonomy. The four genera described for this haptophyte class ( Diacronema Prauser emend. Green et Hibberd, Exanthemachrysis Lepailleur, Pavlova Butcher, and Rebecca Green) were represented by nine different species (one of which with data from GeneBank only). Chlorophylls a , c 1 , c 2 and MgDVP (Mg-[3,8-divinyl]-phytoporphyrin-13 2 methylcarboxylate) and the carotenoids fucoxanthin, diadinoxanthin, diatoxanthin, and � , � -carotene were detected in all cultures. Species only differed in the content of an unknown (diadinoxanthin-like) xanthophyll and two polar chl c forms, identified as a monovinyl (chl c 1 -like) and a divinyl (chl c 2 -like) compound. This is the first observation of the monovinyl form in haptophytes. Based on distribution of these two chl c forms, species were separated into Pavlovophyceae pigment types A, B, and C. These pigment types crossed taxonomic boundaries at the generic level but were in complete accordance with species groupings based on molecular phylogenetic relationships and certain ultrastructural characteristics (position and nature of pyrenoid, stigma, and flagella). These results suggest that characterization of the pigment signature of unidentified culture strains of Pavlovophyceae can be used to predict their phylogenetic affinities and vice versa. Additional studies have been initiated to evaluate this possibility for the haptophyte class Prymnesiophyceae.

Isochrysis galbana was cultured heterotrophicallywith glucose and mannose as a potential food for larval Pacific oyster,Crassostrea gigas. The food was evaluated in terms offeeding experiments and changes in sterol composition. The larvae showed delayedgrowth and higher mortality compared with ones fed light-grown material, with asignificant difference in mortality from day 8. Light-grown I.galbana contained three major sterols (24-oxocholesterol acetate,ergost-5-en-3β-ol, and cholest-5-en-24-1,3-(acetyloxy)-,3β-ol) and twominor sterols (24-methylcholesta-5,22-dien-3β-ol and24-methylcholest-5-en-3β-ol). The sterol content decreased markedly aftertransfer to dark culture, especially in two of the major sterols,24-oxocholesterol acetate and ergost-5-en-3β-ol. The other major sterol,cholest-5-en-24-1,3-(acetyloxy)-,3β-ol, fall to about 50% of theautotrophic control by day 12. These results indicate that heterotrophicallygrown I. galbana is not a favorable alternative to normallygrown material for larval C. gigas culture as far as sterolcomposition is concerned.

Microscopical and molecular analyses were used to investigate the diversity and spatial community structure of spring phytoplankton all along the estuarine gradient in a macrotidal ecosystem, the Baie des Veys (eastern English Channel). Taxa distribution at high tide in the water column appeared to be mainly driven by the tidal force which superimposed on the natural salinity gradient, resulting in a two-layer flow within the channel. Lowest taxa richness and abundance were found in the bay where Teleaulax-like cryptophytes dominated. A shift in species composition occurred towards the mouth of the river, with the diatom Asterionellopsis glacialis dramatically accumulating in the bottom waters of the upstream brackish reach. Small thalassiosiroid diatoms dominated the upper layer river community, where taxa richness was higher. Through the construction of partial 18S rDNA clone libraries, the microeukaryotic diversity was further explored for three samples selected along the surface salinity gradient (freshwater - brackish - marine). Clone libraries revealed a high diversity among heterotrophic and/or small-sized protists which were undetected by microscopy. Among them, a rich variety of Chrysophyceae and other lineages (e.g. novel marine stramenopiles) are reported here for the first time in this transition area. However, conventional microscopy remains more efficient in revealing the high diversity of phototrophic taxa, low in abundances but morphologically distinct, that is overlooked by the molecular approach. The differences between microscopical and molecular analyses and their limitations are discussed here, pointing out the complementarities of both approaches, for a thorough phytoplankton community description. peerReviewed

International audience; Estuaries and coastal lagoons are included within the transitional waters category, according to the Water Framework Directive. However, criteria for their differentiation and characterisation are still under discussion and require more research. In particular, detailed observations of biodiversity in more complex transitional and coastal waters are lacking. Microscopic and molecular analyses were therefore used to investigate phytoplankton diversity and spatial community structure, in early spring, along the freshwater-to-marine continuum of the Segura River (Spain), an intensively regulated semiarid basin discharging into the Mediterranean Sea. In addition to the salinity gradient as the major factor determining taxa distribution, influence of multiple anthropogenic and climatic impacting factors (drought, confined waters, irrigation canal) leads to a significant spatial heterogeneity of the aquatic habitat types associated with variations in community composition. Several shifts within the phytoplankton distribution pattern along the continuum are revealed using multivariate analyses. An impressive bloom of the cryptophyte Plagioselmis prolonga occurred in the mixing zone, associated with a typical euryhaline community indicative of eutrophication. The 18S rDNA diversity revealed a microeukaryotic richness including several little-known groups, heterotrophic representatives, and potential parasites. By combining morphological and molecular approaches we revealed the presence of a ‘hidden’ diversity often neglected in traditional surveys.

Experiments were performed to examine the response of sterol metabolism in diploid and triploid Japanese oysters Crassostrea gigas (Thunberg) that had been conditioned for sexual maturation or unfed for 30 days. Free sterols were extracted, separated, identified and quantified by gas chromatography and gas chromatography–mass spectrometry for pooled samples of ten oysters from each of six treatments (two reference controls, diploid unfed and conditioned, and triploid unfed and conditioned). Effects of feeding regimes on total sterol contents were observed and the metabolism of sterols is discussed. Both unfeeding and conditioning appeared to influence the sterol pattern. Unfeeding increased sterol content regardless of ploidy level, suggesting a mainly structural role for these molecules. Conditioning led to an even greater rise in sterol content, but in diploid oysters only. These changes are discussed with regard to gametogenesis. Further study is needed to determine whether any individual variations among oysters would have affected our data.

The sterols of seven unicellular algae widely used in mariculture and belonging to different classes (Prasinophyceae, Haptophyceae, Eustigmatophyceae, and Diatomophyceae) were examined for free and combined forms. Under standard culture conditions, all synthesized free sterols and combined forms (steryl esters, acyl steryl glycosides, and steryl glycosides). Free sterols were dominant in five of the species. In contrast, sterols were mostly esterified in the eustigmatophyte Nannochloropsis oculata (Droop) Hibberd and the diatom Thalassiosira pseudonana Hasle et Heimdal, whereas in another diatom, Chaetoceros calcitrans (Paulsen) Takano, glycosylated forms represented over 60% of total sterols. The pennate diatom Haslea ostrearia (Gaillon) Simonsen synthesized large amounts of steryl glycosides consisting mainly of an unusual sterol, 23,24-dimethylcholest-5-en-3β-ol, occurring in some dinoflagellates.

The diversity of Pseudo-nitzschia (Bacillariophyceae) and accumulation of the neurotoxin domoic acid (DA) in two types of shellfish; tuberculate cockles (Acanthocardia tuberculata) and sweet clams (Challista chione) was explored in M’diq Bay,Morocco during 2007. The highest abundances of Pseudo-nitzschia were found during the period from March to October, with peaks occurring in May and September. Toxin analysis showed an accumulation of domoic acid in shellfish sampled during spring and autumn. The maximum toxin concentration was 4.9 mg DAg-1 of the whole tissue recorded in sweet clam during spring. Using transmission electron microscopy, thirteen Pseudo-nitzschia species were identified, eight of which are known as producers of domoic acid: P. multistriata, P. cuspidata, P. galaxiae, P. multiseries, P. pseudodelicatissima, P. pungens var. aveirensis, P. calliantha and P. fraudulenta. The five non- toxic species observed were P. subpacifica, P. arenysensis, P. dolorosa, P. subfraudulenta, and P. cf. caciantha

Pavlova lutheri was examined for free and combined sterols. Eight common desmethylsterols represented more than 49% of the total sterols. The principal sterols of this group were poriferasterol, 5-ergostenol and cholesterol. Four uncommon sterols were also detected: a methylsterol (4α-methyl-24β-ethylcholest-22(23)-en-3β-ol) and three 4α-methyldihydroxysterols (4α-methylpavlovols). 4α-Methylsterol is the dominant sterol and along with the pavlovols accounts for more than half the total sterols of P. lutheri. End products of sterol biosynthetic pathways were present in almost all forms, in contrast to intermediate products. The dominant 4α-methylsterol occurred exclusively in free form, in contrast to the pavlovols, which were present as glycoside conjugates only. This peculiar distribution and conjugation of sterols is discussed.

International audience; Background: DNA barcoding offers an efficient way to determine species identification and to measure biodiversity. For dinoflagellates, an ancient alveolate group of about 2000 described extant species, DNA barcoding studies have revealed large amounts of unrecognized species diversity, most of which is not represented in culture collections. To date, two mitochondrial gene markers, Cytochrome Oxidase I (COI) and Cytochrome b oxidase (COB), have been used to assess DNA barcoding in dinoflagellates, and both failed to amplify all taxa and suffered from low resolution. Nevertheless, both genes yielded many examples of morphospecies showing cryptic speciation and morphologically distinct named species being genetically similar, highlighting the need for a common marker. For example, a large number of cultured Symbiodinium strains have neither taxonomic identification, nor a common measure of diversity that can be used to compare this genus to other dinoflagellates. Methodology/Principal Findings: The purpose of this study was to evaluate the Internal Transcribed Spacer units 1 and 2 (ITS) of the rDNA operon, as a high resolution marker for distinguishing species dinoflagellates in culture. In our study, from 78 different species, the ITS barcode clearly differentiated species from genera and could identify 96% of strains to a known species or sub-genus grouping. 8.3% showed evidence of being cryptic species. A quarter of strains identified had no previous species identification. The greatest levels of hidden biodiversity came from Scrippsiella and the Pfiesteriaceae family, whilst Heterocapsa strains showed a high level of mismatch to their given species name. Conclusions/Significance: The ITS marker was successful in confirming species, revealing hidden diversity in culture collections. This marker, however, may have limited use for environmental barcoding due to paralogues, the potential for unidentifiable chimaeras and priming across taxa. In these cases ITS would serve well in combination with other markers or for specific taxon studies.

International audience; Time series of soluble extracellular polymeric substance (S-EPS) and transparent exopolymer particle (TEP) fractions, as well as biological, physical and chemical parameters, were studied in natural phytoplankton assemblages at 2 macrotidal sites located in the English Channel for 3 yr. The first site, the Bay des Veys (BDV), is sheltered from prevailing winds and influenced by a high river discharge, whereas the second, Lingreville-sur Mer (LGV), is exposed to the open ocean and to dominant winds. At both sites, the highest TEP concentrations were measured in spring and summer (1735 and 3604 μg equiv X l-1 at BDV and LGV, respectively) and were correlated with phytoplankton biomass and nitrogen concentrations. During the autumn and winter, TEP dynamics were not related to phytoplankton dynamics but appeared controlled by hydrodynamics. In contrast to TEP concentrations, S-EPS did not present any seasonal dynamics and was not correlated with TEP variations. The highest amount of S-EPS was recorded in spring at LGV (25.8 mg equiv. glucose l-1) and in summer at BDV (26.4 mg equiv. glucose l-1). The S-EPS pool was separated in 2 fractions according to the molecular weight: low (LW) and high (HW). The LW fraction was produced in higher quantity than the HW fraction, and with larger temporal fluctuations. Therefore, both S-EPS fractions seem controlled by different environmental parameters depending on the season and on the studied ecosystem. The different dynamics observed for TEP and S-EPS confirm the complexity of carbon excretion processes in phytoplankton, and the results reveal different metabolic pathways and different origins for these carbon excretions.

Temporal variations in the Pseudo-nitzschia assemblage were characterized in the Baie des Veys (Normandy, France) from July 2007 to July 2008. This study describes the succession of Pseudo-nitzschia species. Six species were identified, Pseudo-nitzschia americana , P. australis , P. delicatissima , P. fraudulenta , P. multistriata , and P. pungens and their occurrences were related to physical, chemical and biological factors. Pseudo-nitzschia spp. were observed during the whole year, the higher abundance (38 × 10 3 cell L −1 ) and diversity were found in September while the lowest (0.9 × 10 3 cell L −1 ) were observed from October to the end of February. P. americana and P. australis were only seen in September and were positively correlated with high chlorophyll a, temperature and Si(OH) 4 concentrations. P. delicatissima and P. fraudulenta were more abundant under high NO 3 and low Si(OH) 4 concentrations and associated with low chlorophyll a concentrations. P. multistriata appeared in October and in November 2007 and its abundance was correlated with NH 4 while P. pungens abundance was not related to any environmental factors tested suggesting high acclimation capacities. In September 2007, P. australis was observed and domoic acid (7.1 ng DA L −1 ) was measured in the phytoplankton samples. During this period, the phytoplankton population was mostly limited by PO 4 and NO 3 concentrations. On 17 September a heavy rainfall (15.6 mm) affected the nutrient stocks resulting in Si(OH) 4 and NO 3 limitations. Our results suggest that this Si(OH) 4 limitation might have promoted the production of domoic acid by P. australis . This study presents the first results on Pseudo-nitzschia successions and particulate domoic acid concentrations on the French coasts. This work especially highlights the beginning of autumn as a potential risk period for ASP events linked to P. australis development in the Baie de Seine.

The brown seaweed Sargassum vulgare is abundant along the coast of Rio de Janeiro state. An investigation of the spatial variation of antifouling activity was conducted, in which algae were collected at five locations along the coast of Rio de Janeiro during October 2008. Hexane, dichloromethane, methanol and acetone/water extracts were prepared and screened for their bioactivities against the growth of five strains of marine fouling bacteria, five biofilm-associated microphytobenthic strains and attachment of the mussel Perna perna. The most active were the hexane extracts from Bananal algae that inhibited the growth of all microalgae tested; the methanol and dichloromethane extracts from Mar do Norte, which inhibited Vibrio aestuarianus and Pseudoalteromonas elyakovii and the polyphenol extracts from Ilha de Itacuruca and Bananal that inhibited mussel attachment, respectively, by 64% and 71% compared to controls.

International audience; The short-term dynamics (time scale of a few days) of phytoplankton communities in coastal ecosystems, particularly those of toxic species, are often neglected. Such phenomena can be important, especially since these very species can endanger the sustainability of shellfish farming. In this study, we investigated the short-term changes in phytoplankton community structure (species succession) in two coastal zones in parallel with physical and chemical conditions. Mixing events with allochtonous waters could thus be distinguished from local processes associated with population growth when it was associated with a change in light or nutrient limitation. Mixing events and water advection influenced fluctuations in total phytoplankton biomass and concentration of dominant species, while local processes influenced delayed changes in community structure. The estuarine species Asterionellopsis glacialis increased in concentration when the water mass mixed with the nearest estuarine water masses. The biological response, measured as photosynthetic capacity, occurred after a time-lag of a few hours, while the changes in community structure occurred after a time-lag of a few days. Finally, the coastal water mass was constantly mixed with both the nearest estuarine and marine water masses, leading in turn to delayed changes in phytoplankton community structure. These changes in species composition and dominance were observed on a time scale of a few days, which means that some toxic species may be missed with a biweekly sampling strategy.

Marine macroalgae are particularly prone to epiphytism. The colonisation of their surface may lead to severe perturbations and sometimes to the death of the host. To protect themselves against settling and/or competing organisms, many algae have developed defences against fouling by producing a wide variety of chemically active metabolites. The goal of this study was to investigate potential anti-microfouling activities of two introduced algal species from the Brittany coast (France), Sargassum muticum (Phaeophyceae) and Grateloupia turuturu (Rhodophyceae). Thus, a complete study of the antimicrobial activities of extracts (aqueous, acetone, chloroform, dichloromethane, diethyl-ether, ethyl acetate, ethanol 96°, hexane and methanol) from S. muticum and G. turuturu against marine fouling bacteria (5 strains), fungi (5 strains) and biofilm-associated microphytobenthic strains (5) were performed. The most active extract of G. turuturu was the dichloromethane fraction, while the chloroform extract from S. muticum showed some good results. Our data suggest that these macroalgae can provide useful compounds or templates for industrial anti-microfouling applications.

International audience

Four unidentified new strains of Pavlovophyceae [Pavlova sp. AC 250 (Pfl), Pavlova sp. AC 248 (Psh), Pavlova sp. AC 251 (Pth), Pavlova sp. AC 538 (Psm)] and two known species [Pavlova pinguis (Ppi), Rebecca salina (ex Pavlova salina, Rsa)] were characterized (productivity, size, dry weight, ash, gross composition, fatty acids, sterols) and their nutritional value in bispecific diets were evaluated both on Crassostrea gigas and Pecten maximus larvae. All microalgae exhibited poor food value for C. gigas larvae. P. pinguis and R. salina did not sustain any growth, like the control starved larvae. No exo-toxicity of P. pinguis and R. salina was detected. These two species were weakly ingested by C. gigas larvae, while the four other pavlovophytes were effectively grazed. When used as food for P. maximus larvae, P. pinguis and Psh led to poor development. In contrast, a diet with Pfl resulted in significantly better growth than the control.

Links between short-term variability of phytoplankton primary production and community structure changes have been studied rarely. This has been examined in a macrotidal ecosystem, the Baie des Veys (eastern English Channel, France), in 2003 and 2004, over the complete tidal cycle (semi-diurnal mode, 12 h). Within this area, primary production and photosynthetic parameter estimates, according to the 14C incorporation technique, were supported by an exhaustive taxonomic study and measurements of physicochemical factors to illustrate the environmental framework. Related to the river Vire discharge, daily interactions between estuarine and bay waters were demonstrated. Depth-integrated primary production Pz was maximal around noon in the bay (48.7–68.0 mg C m−2 h−1) and decreased through the day in the mouth of the river. Photosynthetic parameters' variations and photoacclimation were influenced by the ecosystem variability level: short-term photoacclimation was possible in low mixing conditions. Changes in taxonomic composition according to tidal forcing led to variations in primary production levels. Large species, associated with high photosynthetic parameters, were observed in the bay, whereas small ones were present in the mouth of the river, when low primary production was measured. On a short-time scale, a positive relationship was observed between species diversity and primary production. This work emphasizes the need to focus on changes in phytoplankton community structure in order to understand short-term variability in primary production.

International audience; The Pavlovophyceae (Haptophyta) contains four genera (Pavlova, Diacronema, Exanthemachrysis and Rebecca) and only thirteen characterised species, several of which are important in ecological and economic contexts. We have constructed molecular phylogenies inferred from sequencing of ribosomal gene markers with comprehensive coverage of the described diversity, using type strains when available, together with additional cultured strains. The morphology and ultrastructure of 12 of the described species was also re-examined and the pigment signatures of many culture strains were determined. The molecular analysis revealed that sequences of all described species differed, although those of Pavlova gyrans and P. pinguis were nearly identical, these potentially forming a single cryptic species complex. Four well-delineated genetic clades were identified, one of which included species of both Pavlova and Diacronema. Unique combinations of morphological/ultrastructural characters were identified for each of these clades. The ancestral pigment signature of the Pavlovophyceae consisted of a basic set of pigments plus MV chl cPAV, the latter being entirely absent in the Pavlova + Diacronema clade and supplemented by DV chl cPAV in part of the Exanthemachrysis clade. Based on this combination of characters, we propose a taxonomic revision of the class, with transfer of several Pavlova species to an emended Diacronema genus. The evolution of the class is discussed in the context of the phylogenetic reconstruction presented. (C) 2011 Elsevier GmbH. All rights reserved.

Background: Dinoflagellates are an ecologically important group of protists with important functions as primary producers, coral symbionts and in toxic red tides. Although widely studied, the natural diversity of dinoflagellates is not well known. DNA barcoding has been utilized successfully for many protist groups. We used this approach to systematically sample known ‘‘species’’, as a reference to measure the natural diversity in three marine environments. Methodology/Principal Findings: In this study, we assembled a large cytochrome c oxidase 1 (COI) barcode database from 8 public algal culture collections plus 3 private collections worldwide resulting in 336 individual barcodes linked to specific cultures. We demonstrate that COI can identify to the species level in 15 dinoflagellate genera, generally in agreement with existing species names. Exceptions were found in species belonging to genera that were generally already known to be taxonomically challenging, such as Alexandrium or Symbiodinium. Using this barcode database as a baseline for cultured dinoflagellate diversity, we investigated the natural diversity in three diverse marine environments (Northeast Pacific, Northwest Atlantic, and Caribbean), including an evaluation of single-cell barcoding to identify uncultivated groups. From all three environments, the great majority of barcodes were not represented by any known cultured dinoflagellate, and we also observed an explosion in the diversity of genera that previously contained a modest number of known species, belonging to Kareniaceae. In total, 91.5% of non-identical environmental barcodes represent distinct species, but only 51 out of 603 unique environmental barcodes could be linked to cultured species using a conservative cut-off based on distances between cultured species. Conclusions/Significance: COI barcoding was successful in identifying species from 70% of cultured genera. When applied to environmental samples, it revealed a massive amount of natural diversity in dinoflagellates. This highlights the extent to which we underestimate microbial diversity in the environment.

International audience; This study of Gymnodinium catenatum was conducted across two sampling stations; M'diq bay and Oued Laou estuary during the period from July 2007 to May 2009. Gymnodinium catenatum blooms occurred after a rainfall event in autumn and early winter. Statically analyses showed a positive correlation with rainfall. During January 2008, the G. catenatum bloom resulted in contamination of tuberculate cockles and sweet clam by Paralytic Shellfish Poisoning (PSP) toxins. In the Oued Laou estuary, the levels of these toxins in shellfish went beyond the normative threshold for consumption of shellfish, (80 µg SXTeq. /100g of meat) and reached (710 ± 82.07) and (198 ± 6.56) µg SXTeq. /100g of meat in cockles and sweet clam respectively. In M'diq bay, concentrations of PSP toxins in the meat of these two shellfish were lower (256.57 ± 12.22 µg SXTeq. /100g and 80.66 ± 8.14 µg SXTeq. /100g of meat in tuberculate cockles and sweet clam respectively. An experimental test of depuration of tuberculate cockles and sweet clam contaminated by the PSP toxins was conducted in laboratory conditions in the first week of January 2008. The results showed partial and progressive elimination of PSP toxins in two shellfish species over time. In the tuberculate cockle, the elimination of PSP appears to be slower compared with the sweet clam; it took 120 days to reach levels of 80 µg SXTeq. /100g of meat, on the other hand only 3 days were needed to reach this safe concentration in the sweet clam.