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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. Source


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. Source


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. Source


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. Source


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. Source

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