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Rasconi S.,CNRS Microorganisms Laboratory: Genome and Environment | Rasconi S.,University of Oslo | Niquil N.,CNRS Coastal and Marine Environment Laboratory | Sime-Ngando T.,CNRS Microorganisms Laboratory: Genome and Environment
Environmental Microbiology | Year: 2012

Fungal parasitism is recurrent in plankton communities, especially in the form of parasitic chytrids. However, few attempts have been made to study the community structure and activity of parasites at the natural community level. To analyse the dynamics of zoosporic fungal parasites (i.e. chytrids) of phytoplankton, samples were collected from February to December 2007 in two freshwater lakes. Infective chytrids were omnipresent in lakes, with higher diversity of parasites and infected phytoplankton than in previous studies. The abundance and biomass of parasites were significantly higher in the productive Lake Aydat than in the oligomesotrophic Lake Pavin, while the infection prevalence in both lakes were similar and averaged about 20%. The host species composition and their size appeared as critical for chytrid infectivity, the larger hosts being more vulnerable, including pennate diatoms and desmids in both lakes. The highest prevalence (98%) was noted for the autumn bloom of the cyanobacterium Anabaena flosaquae facing the parasite Rhizosiphon crassum in Lake Aydat. Because parasites killed their hosts, this implies that cyanobacterial blooms, and other large size inedible phytoplankton blooms as well, may not totally represent trophic bottlenecks because their zoosporic parasites can release dissolved substrates for microbial processes through host destruction, and provide energetic particles as zoospores for grazers. Overall, we conclude that the parasitism by zoosporic fungi represents an important ecological driving force in the food web dynamics of aquatic ecosystems, and infer general empirical models on chytrid seasonality and trophodynamics in lakes. © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd.

Milinkovitch T.,CNRS Coastal and Marine Environment Laboratory | Kanan R.,CEDRE | Thomas-Guyon H.,CNRS Coastal and Marine Environment Laboratory | Le Floch S.,CEDRE
Science of the Total Environment | Year: 2011

Dispersing an oil slick is considered to be an effective response to offshore oil spills. However, in nearshore areas, dispersant application is a controversial countermeasure: environmental benefits are counteracted by the toxicity of dispersant use. In our study, the actual toxicity of the dispersant response technique in the nearshore areas was evaluated through an experimental approach using juvenile Liza ramada. Fish were contaminated via the water column (i) by chemically dispersed oil, simulating dispersant application, (ii) by dispersant, as an internal control of chemical dispersion, (iii) by mechanically dispersed oil, simulating only the effect of natural mixing processes, without dispersant application, and (iv) by the water soluble fraction of oil, simulating the toxicity of an oil slick before recovery. Bioconcentrations of polycyclic aromatic hydrocarbons (PAH) and mortality were evaluated, and related to both total petroleum hydrocarbon (TPH) and polycyclic aromatic hydrocarbon (PAH) concentrations in seawater.Fish exposed to chemically dispersed oil showed both a higher bioconcentration of PAH and a higher mortality than fish exposed to either the water soluble fraction of oil or the mechanically dispersed oil. These results suggest that (i) dispersion is a more toxic response technique than containment and recovery of the oil slick; (ii) in turbulent mixing areas, dispersant application increases the environmental risk for aquatic organisms living in the water column. Even if the experimental aspects of this study compel us to be cautious with our conclusions, responders could consider these results to establish a framework for dispersant use in nearshore areas. © 2010 Elsevier B.V.

Becker M.,IRD Montpellier | Karpytchev M.,CNRS Coastal and Marine Environment Laboratory | Lennartz-Sassinek S.,University of Cologne
Geophysical Research Letters | Year: 2014

Detection and attribution of human influence on sea level rise are important topics that have not yet been explored in depth. We question whether the sea level changes (SLC) over the past century were natural in origin. SLC exhibit power law long-term correlations. By estimating Hurst exponent through Detrended Fluctuation Analysis and by applying statistics of Lennartz and Bunde [], we search the lower bounds of statistically significant external sea level trends in longest tidal records worldwide. We provide statistical evidences that the observed SLC, at global and regional scales, is beyond its natural internal variability. The minimum anthropogenic sea level trend (MASLT) contributes to the observed sea level rise more than 50% in New York, Baltimore, San Diego, Marseille, and Mumbai. A MASLT is about 1mm/yr in global sea level reconstructions that is more than half of the total observed sea level trend during the XXth century. Key Points Long-term persistence impacts on sea level rise estimation Sea level change is clearly unnatural in two thirds of the longest tidal records Sea level change magnitude cannot be explained without human influence © 2014. American Geophysical Union. All Rights Reserved.

Legendre L.,University Pierre and Marie Curie | Legendre L.,CNRS Oceanography Laboratory of Villefranche | Niquil N.,CNRS Coastal and Marine Environment Laboratory
Journal of Marine Systems | Year: 2013

Large-scale regional marine ecosystems can be compared for various processes that include their structure and biodiversity, functioning, services, and effects on biogeochemical processes. The comparisons can proceed from data up, or from conceptual models down, or from a combination of models and data. This study proposes a typology of methods and approaches that are currently used, or could possibly be used for making large-scale ecosystem comparisons. The various methods and approaches are illustrated with examples drawn from the literature. © 2011 Elsevier B.V.

Viricel A.,CNRS Coastal and Marine Environment Laboratory | Pante E.,CNRS Coastal and Marine Environment Laboratory | Dabin W.,University of La Rochelle | Simon-Bouhet B.,CNRS Coastal and Marine Environment Laboratory
Molecular Ecology Resources | Year: 2014

Restriction-site-associated DNA tag (RAD-tag) sequencing has become a popular approach to generate thousands of SNPs used to address diverse questions in population genomics. Comparatively, the suitability of RAD-tag genotyping to address evolutionary questions across divergent species has been the subject of only a few recent studies. Here, we evaluate the applicability of this approach to conduct genome-wide scans for polymorphisms across two cetacean species belonging to distinct families: the short-beaked common dolphin (Delphinus delphis; n = 5 individuals) and the harbour porpoise (Phocoena phocoena; n = 1 individual). Additionally, we explore the effects of varying two parameters in the Stacks analysis pipeline on the number of loci and level of divergence obtained. We observed a 34% drop in the total number of loci that were present in all individuals when analysing individuals from the distinct families compared with analyses restricted to intraspecific comparisons (i.e. within D. delphis). Despite relatively stringent quality filters, 3595 polymorphic loci were retrieved from our interfamilial comparison. Cetaceans have undergone rapid diversification, and the estimated divergence time between the two families is relatively recent (14-19 Ma). Thus, our results showed that, for this level of divergence, a large number of orthologous loci can still be genotyped using this approach, which is on par with two recent in silico studies. Our findings constitute one of the first empirical investigations using RAD-tag sequencing at this level of divergence and highlights the great potential of this approach in comparative studies and to address evolutionary questions. © 2013 John Wiley & Sons Ltd.

Marrou L.,CNRS Coastal and Marine Environment Laboratory
Journal of Coastal Research | Year: 2011

The French marina of La Rochelle is one of the most important o the European Atlantic Coast with nearly 3,500 rings and a broad range of seaside activities ranging from nautical building to shiplanding activities including great international nautical events. The prospect of the creation of Marina Natural Park of the Estuary of the Gironde and the Pertuis Charentais makes us focus on the issue of the nautical frequentation in the Pertuis Archipelago. The coast of La Rochelle shelters the marina of Les Minimes, a fishing harbour (called La Pallice). Therefore the traffic is potentially important and it is necessary to know how much and what goes on in order to make the traffic safe and to regulate it properly. The rational marine planning is interesting as this coast shelters one of the most important French Oyster and Mussel production unit. So we tried to know better the frequentation of the Bay of La Rochelle focusing on the analysis of marina practices. The approach we selected relies on enquiries, counting analysis, observations from land, ad from sea as well as from the air. The first results (2008 and 2009 collects) account for situations quite different from those known up to now: there are numerous sea-outings and a huge difference between the use of sailing boats or motorboats. The selective occupation of the Bay can also be observed. Consequently, these results are liable to change the marina management. © 2011 Coastal Education & Research Foundation.

Duvat V.,CNRS Coastal and Marine Environment Laboratory
Sustainability Science | Year: 2013

In the context of rapid population growth and urbanization, atoll countries have engaged in reclamation works and in the construction of coastal defences to extend inhabitable areas and reduce the threats posed by coastal erosion and flooding. Despite their major role in asset protection, coastal structures are still poorly documented. However, a better knowledge of the characteristics of these structures (location, type, condition, management status, etc.) would facilitate the establishment of consistent construction and maintenance programmes, and also contribute to a better understanding of shoreline changes. To address this need, this paper provides an assessment of coastal structures on Tarawa Atoll in Kiribati. The results highlight the abundance of structures, mostly seawalls (94.7 % of the total), which stretch along 29 % of the coastline. The protected shoreline decreases from urban (53.9 % at Bairiki) to rural islands (27.3 % at Buota), in proportion to population pressure. The occurrence and height of structures are greater on windward, ocean shores than on lagoon shores. Seawall condition is better in rural islands, compared to urban and semi-urban areas. The observed differences in the characteristics and physical condition of coastal structures mainly reflect differences in the management status of structures and the availability of building materials and funding. More generally, the occurrence and characteristics of coastal structures are strongly correlated to population densities, land-use dynamics and shoreline mobility. At some locations, the failure of coastal protection highlights the seriousness of the problems raised by land-use practices in Tarawa. © 2013 Springer Japan.

Proust D.,CNRS Coastal and Marine Environment Laboratory
Journal of Soils and Sediments | Year: 2014

Purpose: Conventional pedological survey generally assesses soil metal pollution by comparing total metal concentrations in soil to geochemical baselines in parent rock. This global approach overlooks the sorption capacities of the clay minerals which form at micrometric scale in weathering microsystems and are essential for the behaviour of metals in soil. Therefore, our aim was to investigate the impact of these weathering microsystems and their clay mineralogy upon Zn sorption and distribution throughout a sludge-contaminated soil. Materials and methods: Two soil profiles with the same diorite parent rock were sampled: (i) an amended soil profile (AS) that received for 10 years wet sewage sludges heavily loaded with Zn and (ii) a control soil profile (CS) free of sludge spreading. Soil samples were carefully collected as undisturbed blocks using plastic core samplers to prevent sample metal contamination. Each sample was further divided into two subsamples: the first was devoted to bulk chemical analyses, mineral grains separation and X-ray diffraction (XRD) analyses, whereas the second part was used for thin-section preparation and electron probe microanalyses (EPMA). Results and discussion: Zn in the control soil is inherited from the weathering parent rock, whereas it is supplied at the surface of the amended soil by sludges spreading. Each rock-forming mineral weathers into specific clay minerals: amphibole into saponite and montmorillonite and plagioclase into montmorillonite and kaolinite. Each clay mineral, with its specific sorption capacity, controls the Zn distribution within the soil: the smectites produced by the amphiboles have high sorption capacity and favour Zn retention in the upper horizons of the soil; the kaolinites produced by the plagioclases have lower sorption capacity, do not retain Zn in the surface horizons and allow it to migrate to deeper horizons where it is sorbed onto the montmorillonites. Conclusions: The clay minerals appear to be important soil components controlling the mobility of Zn in the contaminated soils. The micrometric mineralogical approach proves to be relevant to describe the importance of the clay mineral species in the Zn fixation at the solid/solution interface. When applied to a wider range of heavy metals and clay minerals, it could be a useful improvement in the surface complexation modelling used to explain metal cation sorption in soils. © 2014, Springer-Verlag Berlin Heidelberg.

Lavaud J.,CNRS Coastal and Marine Environment Laboratory | Lepetit B.,CNRS Coastal and Marine Environment Laboratory
Biochimica et Biophysica Acta - Bioenergetics | Year: 2013

Diatoms are a major group of microalgae whose photosynthetic productivity supports a substantial part of the aquatic primary production. In their natural environment they have to cope with strong fluctuations of the light climate which can be harmful for photosynthesis. In order to prevent the damage of their photosynthetic machinery, diatoms use fast regulatory processes among which the non-photochemical quenching of chlorophyll a fluorescence (NPQ) is one of the most important. In a previous work, we highlighted differences in the kinetics and extent of NPQ between diatom species/strains originating from different aquatic habitats. We proposed that the NPQ differences observed between strains/species could potentially participate to their ecophysiological adaptation to the light environment of their respective natural habitat. In order to better understand the molecular bases of such differences, we compared the NPQ features of four strains/species of diatoms known for their NPQ discrepancy. We could identify new spectroscopic fingerprints concomitant to NPQ and the related xanthophyll cycle. These fingerprints helped us propose a molecular explanation for the NPQ differences observed between the diatom species/strains examined. The present work further strengthens the potential role of NPQ in the ecophysiology of diatoms. © 2012 Elsevier B.V.

Bertin X.,CNRS Coastal and Marine Environment Laboratory | Prouteau E.,CNRS Coastal and Marine Environment Laboratory | Letetrel C.,CNRS Coastal and Marine Environment Laboratory
Global and Planetary Change | Year: 2013

A new 109year numerical wind-wave hindcast is developed for the North Atlantic Ocean based on the 20th century atmospheric reanalysis (20CR). Wave results are validated directly against data originating from voluntary observing ships and satellite altimetry in the North-East Atlantic Ocean. The normalized error for yearly-mean significant wave height (Hs) is shown to be of the order of 5% for the second part of the 20th century. An indirect validation is also performed through 10m wind speed and suggests that the accuracy of yearly-mean Hs only slightly decreases for the beginning of the 20th century. The comparison between Hs and the index of the North Atlantic Oscillation revealed that this phenomenon partly controls Hs inter-annual variability, with a positive (negative) correlation in the northeastern (southwestern) part of the study area. The analysis of model results shows an increase in Hs over the whole North Atlantic Ocean superimposed to the inter-annual variability, reaching 0.01m.yr-1 (20 to 40% over the 20th century) north of 50°N. This increase is explained by a rise in wind speed exceeding 20% north of 50°N. The roughening in the wave climate demonstrated in this study is expected to have strong implications for the development of coastal zones and could explain the increase in erosion along the North Atlantic shorelines. © 2013 Elsevier B.V.

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