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The inhibitory effects of crude extracts of Zostera marina L. and Zostera noltii Hornemann on the growth of the toxic red tide dinoflagellate Alexandrium catenella were investigated through bio-assays. Methanolic and aqueous extracts were prepared from fresh and detrital leaves of Z. marina and Z. noltii collected in the Thau lagoon and Arcachon bay (France). All the extracts exhibited significant inhibition of A. catenella growth, whatever the species and without the need of continuous addition of extracts. The effective concentrations (EC 50 ) varied in the range 0.036–0.199 g L −1 for Z. noltii and 0.036–0.239 g L −1 for Z. marina . Methanolic extracts prepared from fresh plant tissues were the most potent, with EC 50 of 0.036–0.039 and 0.036–0.045 g L −1 , for Z. noltii and Z. marina , respectively. After exposure to the extracts, Alexandrium cells exhibited severe morphological anomalies. Hence many cells exhibited a lytic membrane and became necrotic. Cellular degradation appeared dose- and time-dependent. The observed algicidal activities demonstrated the existence of bioactive molecules in the tissues of Zostera leaves, which were stable in the culture medium. The chemical contents of the crude extracts were determined by NMR, LC/MS, and quantitative HPLC. Results showed the predominance of flavonoids and phenolic acids. The total phenolics concentrations correlated negatively with the EC 50 values, suggesting that these secondary metabolites might be responsible for the observed algicidal effects.

Background Cost effective next generation sequencing technologies now enable the production of genomic datasets for many novel planktonic eukaryotes, representing an understudied reservoir of genetic diversity. O. tauri is the smallest free-living photosynthetic eukaryote known to date, a coccoid green alga that was first isolated in 1995 in a lagoon by the Mediterranean sea. Its simple features, ease of culture and the sequencing of its 13 Mb haploid nuclear genome have promoted this microalga as a new model organism for cell biology. Here, we investigated the quality of genome assemblies of Illumina GAIIx 75 bp paired-end reads from Ostreococcus tauri, thereby also improving the existing assembly and showing the genome to be stably maintained in culture. Results The 3 assemblers used, ABySS, CLCBio and Velvet, produced 95% complete genomes in 1402 to 2080 scaffolds with a very low rate of misassembly. Reciprocally, these assemblies improved the original genome assembly by filling in 930 gaps. Combined with additional analysis of raw reads and PCR sequencing effort, 1194 gaps have been solved in total adding up to 460 kb of sequence. Mapping of RNAseq Illumina data on this updated genome led to a twofold reduction in the proportion of multi-exon protein coding genes, representing 19% of the total 7699 protein coding genes. The comparison of the DNA extracted in 2001 and 2009 revealed the fixation of 8 single nucleotide substitutions and 2 deletions during the approximately 6000 generations in the lab. The deletions either knocked out or truncated two predicted transmembrane proteins, including a glutamate-receptor like gene. Conclusion High coverage (>80 fold) paired-end Illumina sequencing enables a high quality 95% complete genome assembly of a compact ~13 Mb haploid eukaryote. This genome sequence has remained stable for 6000 generations of lab culture. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-1103) contains supplementary material, which is available to authorized users.

International audience; Biomass, growth and species composition of siliceous phytoplankton were studied in the Equatorial Pacific during October 1994. Experiments were carried out in different nutrient conditions along the Equator. An oligotrophic area, with nitrate concentrations as low as 10 nM in the upper layer, was encountered in the western part of the transect (166°E–170°W). The concentration of biogenic silica varied from 10 nmol 1−1 in the surface layer up to 40 nmol 1−1 in the deep chlorophyll maximum located near the nutracline. Biogenic silica production, measured by the 32Si method, showed a similar vertical pattern in the nitrate-depleted water, and the mean assimilation rate for Si was 0.4±0.2 nmol l−1 h−1 (integrated mean value: 63 μmol m−2 h−1). In contrast, nitrate concentration ranged from 2 to 4 μM in the surface layer in the high-nutrient low-chlorophyll (HNLC) area located from 170 to 150°W and biogenic silica increased to 200 nmol 1−1. The Si assimilation rate was 1.7±1.0 nmol 1−1 h−1 (integrated mean value: 162 μmol m-Z h−1). In both areas, 80% of Si biomass was concentrated in larger cells ( > 10 μm). Scanning electron microscopy was used to estimate diatom numbers and cell surface areas. This latter parameter correlates well with biogenic silica and warrants a discussion of the contribution of different species to the total biogenic silica. The measured values for specific uptake rate of Si never reached the optimum uptake or growth rate deduced from environmental parameters and kinetic constants reported in the literature. In addition the mean growth rate (0.9±0.3 doubling per day) for the nitrate-depleted water does not differ from the mean value (0.8±0.2 doubling per day) in the HNLC area. Therefore it can be concluded that diatom growth is severely limited in both regions. This agrees well with the nutrient balance study. In the oligotrophic area, N supply appears to be the limiting factor in the upper layer. In the HNLC region, the results of this study are consistent with the hypothesis that diatom growth might be limited by a micro nutrient such as iron. Carbon production by diatoms was estimated to be 31 ± 4 mmol Cm−2 d−1, which is one-third of the total carbon production of the nutrient-enriched area.

The study of the intraspecific variability is a crucial step for understanding the successful establishment and maintenance of invasive species. Alexandrium tamarense strains isolated in spring 2007 from a single bloom in Thau lagoon have been grown on three different media (ESNW based on natural seawater, and the artificial media, ESAW, ESAW+HA). A large diversity in the ability of strains to grow on these media was found. Irrespective of medium compo- sition, growth curves followed three models: (1) a classical shape, (2) a population crash followed in some cases (3) by growth recovery. Some strains were able to show significant growth in an environment completely artificial (ESAW). ANOVA indicated a significant difference between groups in growth rates allowing the distinction of contrasted categories among the strains studied in ESNW medium. These statistical tests also indicated the presence of distinct groups among the strains grown in the ESAW as well as for those on ESAW+HA medium. Lag phases were extremely variable between strains in all environments, suggesting a high variability of adaptation to the environment. The results revealed that wide fitness variations were exhibited by diverse conspecific A. tamarense individuals co-existing during a bloom.

International audience; The role of polyphenols as antioxidants in our daily nutrition has been extensively investigated, but information on composition of tannins from marine sources on nutrient utilisation is limited. This study will be focused on the determination of the polyphenol quantities in brown seaweeds from Brittany coast in France; the extracts were delivered from algae centre for valorisation (CEVA), and the fidelity of the method was examined intraday and interlaboratories. The seaweed's extracts are divided into three categories: Fucus Vesiculosus, Ascophyllum nodosum and Fucus Serratus. Consequently, the total polyphenol contents (TPC) of these extracts will be measured using Folin-Glombitza spectrophotometric method. Thereafter, the antioxidant properties of these polyphenols were determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging. All polyphenols extracted were tested using cyclic voltammetry (CV) in aprotic media. The CV is realised to compare the results from spectroscopic method and to electrochemically characterise the seaweed's polyphenols.

International audience; Eight-month-old blocks of the coral Porites lobata colonized by natural Hawaiian euendolithic and epilithic communities were experimentally exposed to two different aqueous pCO2 treatments, 400 ppmv and 750 ppmv, for 3 months. The chlorophyte Ostreobium quekettii dominated communities at the start and at the end of the experiment (65-90%). There were no significant differences in the relative abundance of euendolithic species, nor were there any differences in bioeroded area at the surface of blocks (27%) between pCO2 treatments. The depth of penetration of filaments of O. quekettii was, however, significantly higher under 750 ppmv (1.4 mm) than under 400 ppmv (1 mm). Consequently, rates of carbonate dissolution measured under elevated pCO2 were 48% higher than under ambient pCO2 (0.46 kg CaCO3 dissolved m-2 a-1 versus 0.31 kg m-2 a-1). Thus, biogenic dissolution of carbonates by euendoliths in coral reefs may be a dominant mechanism of carbonate dissolution in a more acidic ocean.

Sargassum C. Agardh is a genus of marine brown macrophyte classified in the class Phaeophyceae. This genus is distributed worldwide and recognized as the most diversified of the order Fucales. It is especially well represented in the tropical and inter-tropical Pacific where it forms large underwater forests of well known ecological and economical importance. But with more than a thousand taxa described over the last 200 years, and an old and complex classification, identifying a Sargassum species is a difficult task. The Sargassum diversity of the south Pacific islands has been studied here in its Indo-Pacific biogeographical context. A combined morphological and DNA analyses method was applied to recent collections from several Pacific regions. The classification, as well as the taxonomic value of classic morphological characters, was revised. More than 52 news synonymies have been proposed as well as significant revisions of the traditional classification of Sargassum subgenus Sargassum., Sargassum C. Agardh est un genre de macrophyte marine appartenant à la classe des Phaeophyceae. Ce genre est réparti mondialement et reconnu comme un des plus diversifiés de l'ordre des Fucales. Il est particulièrement bien représenté dans le Pacifique tropical et intertropical où il forme de grandes algueraies dont l'importance écologique et l'intérêt économique sont reconnus. Néanmoins, avec près d'un millier de taxons décrits depuis 200 ans, et une classification complexe et ancienne, identifier une espèce de Sargassum est une tâche difficile. La diversité du genre Sargassum des îles du Pacifique Sud a été analysée ici dans son contexte biogéographique Indopacifique. L'étude a été réalisée grâce à une méthode combinée utilisant des analyses morphologiques et ADN sur des collections récentes provenant de plusieurs régions du bassin Pacifique. La classification ainsi que la valeur taxonomique des caractères morphologiques traditionnellement utilisés ont été remis en question. Plus de 52 nouvelles synonymies ont été proposées ainsi que des révisions significatives de la classification traditionnelle du sous-genre Sargassum.

Euendolithic microorganisms (boring microflora) – cyanobacteria, algae and fungi – colonize all carbonate substrates in modern coral reefs and are distributed worldwide. Recent studies showed that in dead carbonate, they are important primary producers and are fed upon by various excavating invertebrate and vertebrate grazers, contributing greatly to biodestruction processes (bioerosion) and sedimentation. Additionally, it has been shown that in some live calcifying organisms, they either inflict damages to live tissues or provide a benefit to the host, depending on the euendolithic community involved (parasitic or mutualistic relationships). Based on those recent studies, the following question is raised: Are euendoliths key organisms in the functioning and maintenance of coral reefs? Reviewed literature includes studies on (1) the mechanisms used by euendoliths to penetrate into carbonate substrates (production of acids or chelating fluids; use of the products of photosynthesis / respiration and / or calcium pumps), (2) their roles in reef bioerosion and sedimentation (major roles), (3) their metabolism (important rates of production), (4) their interactions with their live hosts (symbiosis, mutualism and / or parasitism) and (5) the effects of various environmental factors such as eutrophication, sedimentation and rising atmospheric pCO2 on euendolith activities. The review concentrates on modern coral reef ecosystems.

International audience; This paper focuses on the invasion by Turbinaria ornata (a brown algae) in the Tuamotu archipelago, French Polynesia [(5-35 degrees S)/(200-230 degrees E)]. Prior to 1980, this alga existed only in the Society and Austral archipelagoes. Between 1985 and 1990, it began to appear in the southern and northern parts of the Tuamotu archipelago. Genetic analyses have been shown not to be appropriate in determining the origin of this algae population. This study investigated the possible ocean drift of floating aggregates of algae. Ocean currents were calculated from satellite data from 1993 to 2001. Their spatial variations as well as their seasonal and interannual variations are described along with calculated drift trajectories. While it was found that mean currents cannot directly transport algae from the Society and Austral archipelagoes to the Tuamotu, the large interannual changes during the El Nino-Southern Oscillation phenomenon produce current reversals that are strong enough to create a transport pathway in a short enough time to allow their survival.

In order to study the spatial patterns of genetic diversity of a clonal marine angiosperm, the seagrass Cymodocea nodosa, microsatellite markers were obtained by screening a genomic library enriched for the (CT) dinucleotide motif. Of 38 primer pairs defined, 15 amplified polymorphic microsatellites and are described. These loci identified a number of alleles ranging from two to seven, and showed expected heterozygosity ranging from 0.35 to 0.76, when a group of 40 individuals from Cadiz Bay in Spain was analysed. Additionally, we describe here the multiplexing conditions for 12 of these loci.

© Ifremer/A. Guillou Introduction Dans la Caraïbe, les écosystèmes marins les plus florissants, situés en bordure des côtes, supportent des peuplements originaux. En effet, depuis la fermeture progressive de l’isthme de Panama, commencée durant l’ère tertiaire et achevée il y a environ 3,5 millions d’années, les espèces ont évolué séparément et la faune actuelle de la Caraïbe est différente de celle de l’Indo-Pacifique. Avec près de 70 espèces de coraux, 1 200 de mollusques et 600 de poissons...

La quasi-totalite de la production de biomasse des oceans provient de minuscules organismes photosynthetiques, d'un diametre parfois inferieur au micron. Encore inconnu il y a vingt ans, le picophytoplancton etonne les chercheurs par la richesse de ses formes.

Suite à la récente de l'algue tropicale #Caulerpa taxifolia$ en Méditerranée nord-occidentale, toutes les données disponibles sur la biologie et l'écologie de cette espèce dans l'environnement tropical du lagon néo-calédonien ont été examinées. La distribution spatiale et bathymétrique de cette espèce a été établie grâce à 1772 stations réparties tout autour de la Nouvelle-Calédonie. #C. taxifolia$, présente dans 9% des prélèvements, peut être considérée commeune espèce commune en Nouvelle-Calédonie. Cette espèce se développe principalement sur les fonds de 10 à 30 m. Des observations mensuelles ont montré que sa croissance est maximale au printemps austral. 180 stations choisies au hasard dans le lagon sud-ouest ont permis d'obtenir une biomasse moyenne de O,O46 g de matière sèche sans cendre/m2, ce qui représente une part négligeable (0,18 %) de la biomasse macrophytobenthique des fonds de ce lagon. Sa position dans les réseaux trophiques est malgré tout importante puisqu'elle constitue une source privilégiée de nourriture des sacoglosses, petits mollusques herbivores. (Résumé d'auteur)

Les effets d'extraits commerciaux de l'algue marine #Ascophyllum nodosum$ sur la fécondité du nématode #Meloidogyne javanica$, élevé sur tomate (#Lycopersicon esculentum$ cv. Ailsa Craig) sont évalués. Après une génération, le nombre d'oeufs du nématode récupérés sur les plantes traitées diminue considérablement en comparaison avec les plantes témoins, traitées avec de l'eau pure. Un plus faible nombre d'oeufs sont récupérés sur les plantes infestées par des juvéniles ayant incubé dans des extraits d'algue en comparaison avec les plantes infestées par des juvéniles ayant incubé dans de l'eau pure. (Résumé d'auteur)

Ciguatera fish poisoning (CFP) is acquired through consumption of tropical reef fishes, contaminated with potent neurotoxins, ciguatoxins (CTXs), produced by benthic dinoflagellate of the Gambierdiscus genus. Both spatially and temporally unpredictable, a tainted fish is impossible to differentiate from an untainted one by appearance, taste, texture or odour. Given the predominance of reef fish in the diet of insular countries, the risk of CFP is ever-present. In the Pacific where the incidence of CFP is the highest, the consequences on public health and socio-economy can be extremely severe. Multidisciplinary in nature, the present review revisits the phenomenon of CFP, covering certain of its aspects, notably the etiology, toxicology, ecotoxicology, pharmacology, pathology and the treatments administrated. These aspects of CFP have been reviewed in relation to other poisoning syndromes: tetrodotoxin poisoning and other dinoflagellates- or diatoms-associated intoxications such as paralytic (PSP), diarrhetic (DSP), neurotoxic (NSP), amnesic (ASP) and azaspiracid shellfish poisoning (AZP) and palytoxin poisoning. Based on case reports and bibliographic accounts, a list inventorying the western medicines prescribed to patients suffering from CFP has been established. Within the last two decades, several of the herbal remedies have been evaluated for their efficiencies in in vivo and in a number of in vitro tests, which have also been reviewed herein.

La ciguatera est une intoxication alimentaire par la consommation de poissons de récifs coralliens. Chaque année, en Polynésie française, environ 800 cas d'intoxication font l'objet de déclarations médicales. Le terme "ciguatera" est réservé aux empoisonnements par poisson exception faite des intoxications de type histaminique et des intoxications par tétrodotoxine ou par palytoxine. La ciguatera est considéré comme un problème de santé publique indéniable. Il est aussi et surtout préoccupant à cause de ses répercussions économiques. En effet, l'impact le plus important est lié à son incidence sur le développement de la pêche. L'origine du phénomène est associé à la prolifération dans certaines conditions écologiques d'une algue microscopique, le dinoflagellé toxique #Gambierdiscus toxicus$, Adachi et Fukuyo, et à la transmission de la toxicité aux poissons herbivores et à leurs prédateurs carnivores ichtyophages. Deux familles de toxines sont impliquées

Il est proposé une relation de cause à affet entre les flambées de ciguatera consécutives à une agression subie par une zone récifale et les sorties d'eaux interstitielles par endo upwelling riches en nutriments. Ceux-ci n'étant plus utilisés par un écosystème algo corallien stressé ou éliminé, le sont par des planctontes épibenthiques comme #Gambierdiscus toxicus$ dont la population augmente brutalement. (Résumé d'auteur)

Le rôle joué par les algues benthiques dans l'écosystème corallien est multiple : protection des récifs, maillon de chaînes alimentaires, structure d'accueil de la faune, production de substances diverses. A ce titre, toute fluctuation mesurée à partir d'un état de référence peut être bio-indicatrice. Le satellite SPOT permet, grâce à ses capteurs à haute résolution et à son enregistreur, de fournir la cartographie globale des végétaux marins ainsi que celle des principaux composants de l'écosystème lagonaire de l'île de Moorea (Polynésie française). Cette première approche écologique par satellite se devrait d'être confortée, du fait du développement de pollutions d'origines diverses, par un suivi multitemporel. (Résumé d'auteur)

La divergence et la faible sensibilité des tests de toxicité pour la détection en routine de la ciguatoxine (CTX) ont conduit au développement d'une approche immunoenzymatique. En raison du manque de CTX purifiée, nous avons choisi de travailler avec la monensine, un antibiotique polyéther de faible masse moléculaire et de structure chimique proche à celle de certaines toxines marines. Nous avons tout d'abord défini les conditions optimales de préparation de conjugués haptène-protéine en grosse quantité et, ensuite établi une méthode requièrant seulement 100 ug d'haptène. Des anticorps polyclonaux de lapins et monoclonaux de souris de hautes spécificité et affinité ont pu ainsi être produits. Un microtest ELISA de type compétitif a été mis au point sur plaque de Térasaki, permettant d'abaisser le seuil de détection de la monensine libre à 75 pg. Aucune réaction croisée avec la CTX libre n'a été décelée. La microméthode de préparation des conjugués est actuellement appliquée à une brévétoxine (BTX), une autre toxine de structure chimique semblable à la CTX mais commercialement disponible. (Résumé d'auteur)

Des travaux récents ont été réalisés sur le rôle des bactéries associées aux dinoflagellés. Ils tendent à montrer que les bactéries seraient impliquées dans la production de toxine, voire qu'elles en seraient les productrices. Aucun travail n'ayant à ce jour été réalisé sur les bactéries associées aux dinoflagellés responsables d'intoxication DSP, nous avons extrapolé ces données à ce type de dinoflagellé afin d'évaluer le rôle des bactéries associées à deux dinoflagellés producteurs de DSP (#Prorocentrum lima$ et #Dinophysis spp$) dans la production de toxines. Une étude ultrastructure de ces deux dinoflagellés au MEB a permis de visualiser les très nombreuses bactéries de forme hélicoïdale fixées aux cellules de #P. lima$, ainsi que le faible nombre de bactéries, de forme classique, fixées sur les cellules de #Dinophysis$. Une recherche d'acide okadaïque par dosage HPLC dans les bactéries libres (non fixées aux cellules phytoplanctoniques) a été entreprise dans les cultures de #P. lima$. Les premiers résultats montrent que les bactéries libres associées à #P. lima$ contiendraient une faible quantité d'acide okadaïque; et que la stimulation de la croissance de ces bactéries n'augmente pas la teneur en toxine dans les bactéries libres. (Résumé d'auteur)