2019 |
Le Fur, I., et al. "Re-oligotrophication trajectories of macrophyte assemblages in Mediterranean coastal lagoons based on 17-year time-series." Marine Ecology Progress Series. 608 (2019): 13–32.
Résumé: Since the mid-20th century, Mediterranean lagoons have been affected by eutrophication, leading to significant changes in primary producers. In the early 2000s, management actions have been implemented to reduce nutrient inputs with the aim to achieve a good ecological status as requested by the EU water framework directive. As a result of these actions, a sharp decline in nutrient loads has been recorded in several lagoons leading to an oligotrophication of the water column. The analyses of a long-term data set (1998-2015) of 21 polyhaline and euhaline lagoons with contrasting trophic status allowed us to infer a general scheme for the changes in macrophyte assemblages during the oligotrophication process. Placing hypertrophic and oligotrophic conditions end to end, we inferred that the general pattern for the re-oligotrophication trajectory in Mediterranean coastal lagoons is described by the following sequence, with regime shifts between each state: (1) bare non-vegetated sediments, phytoplankton-dominated state; (2) opportunistic macroalgae; (3) seagrass and perennial macroalgae dominated state. However, we did not observe the latter regime shift for the most eutrophicated lagoons, which, so far, remained stuck in the opportunistic macroalgae state. So far, the shift from dominance of opportunistic macroalgae to a system dominated by seagrasses was only observed in a single lagoon where seagrasses had never completely disappeared, which possibly relates to resilience. More generally, the conditions favoring regime shifts from opportunistic macroalgae to seagrasses are still poorly understood. In conclusion, we describe a generic pattern for re-oligotrophication of Mediterranean coastal lagoons, although a full recovery from highly eutrophied to oligotrophic conditions may require more than a decade and may include conditions that remain so far poorly recognized.
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2018 |
Le Fur, I., et al. "Submerged benthic macrophytes in Mediterranean lagoons: distribution patterns in relation to water chemistry and depth." Hydrobiologia. 808.1 (2018): 175–200.
Résumé: A large spectrum of coastal lagoon types with a wide range of environmental conditions is observed along the French Mediterranean coast. These comprise wide trophic and salinity gradients, ranging from oligotrophic to hypertrophic status, and from nearly freshwater to slightly above marine Mediterranean Sea water salinities, respectively. The statistical analysis of a long-term dataset, including water column variables and observations of macrophyte genera, showed that salinity, depth, and then trophic status, were important factors explaining the distribution of benthic macrophytes for the soft-bottom sediments in the 34 studied French Mediterranean lagoons. Based on this, we assumed that the vegetation succession along the eutrophication gradient was different according to the lagoon salinity ranges. Euhaline and polyhaline lagoons follow the well-known Schramm schematic model, where aquatic angiosperm such as seagrasses dominate under oligotrophic conditions, and opportunistic macroalgae and phytoplankton dominate under eutrophic and hypertrophic conditions. In oligohaline and mesohaline lagoons, the succession is probably an intermediate scheme between the successions observed in small temperate lakes and in marine coastal ecosystems due to the presence of both brackish and freshwater species. We thus propose a conceptual scheme for the oligohaline and mesohaline lagoons.
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Leruste, A., et al. "Complementarity of the multidimensional functional and the taxonomic approaches to study phytoplankton communities in three Mediterranean coastal lagoons of different trophic status." Hydrobiologia. 815.1 (2018): 207–227.
Résumé: We used the individual-based multidimensional functional diversity and the taxonomic approaches in a complementary way to describe phytoplankton communities in three coastal lagoons with different eutrophication status in the South of France. We sampled communities during three seasons, i.e., in autumn, spring, and summer. Using classical taxonomy, 107 taxa/morphotypes were identified in the nine communities. The individual-based functional approach allowed grouping these individuals into 20 functional entities according to their values for 5 traits related to trophic adaptations (cell size, mobility, trophic regime, coloniality, and pelagic/benthic life). Some species (e.g., Prorocentrum micans) emerged in multiple functional entities, showing the importance to consider intraspecific variability. The functional description of phytoplankton communities better reflected the hydrological functioning and the different eutrophication status of the lagoons than the taxonomic approach. Specific functional adaptations were identified in the nine communities. For example, phytoplankton organisms with heterotrophic and potentially mixotrophic abilities occurred when the availability of inorganic nutrient decreased, or when organic matter and small preys were potentially the main nutrient resources. The limitation has also favored small cells highly competitive for nutrients. Using functional indices together with taxonomic description has also helped revealing important aspects of community assembly, such as competitive exclusion in summer.
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Sy, M. M., et al. "Identifying Consensus on Coastal Lagoons Ecosystem Services and Conservation Priorities for an Effective Decision Making: A Q Approach." Ecological Economics. 154 (2018): 1–13.
Résumé: Coastal lagoons ecosystems, while representing benefits for the local populations, have been subjected to high anthropogenic pressures for decades. Hence, conservation measures of these ecosystems are urgently needed and should be combined with their sustainable uses. To address these issues, new research avenues for decision support systems have emphasized the role of the assessment of ecosystem services for establishing conservation priorities by avoiding monetarization approaches. These approaches, because they flatten the various values of nature by projecting them on the single monetary dimension, are often rejected by the stakeholders. We undertake a Q analysis to identify levels of consensus and divergence among stakeholders on the prioritization of ecosystem services provided by two French Mediterranean coastal lagoons areas. The results highlighted that there is a strong consensus among categories of stakeholders in the study sites about the paramount importance of regulation and maintenance services. Three groups of stakeholders, each sharing the same points of view regarding ecosystem services conservation, were identified for each study site. As a non-monetary valuation, Q methodology is very instrumental for the new pluralistic approach of decision support by capturing the values expressed by the stakeholders, without triggering a rejection reflex due to the monetarization.
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2017 |
Audouit, C., et al. "Comparing social representation of water quality in coastal lagoons with normative use of ecological indicators." Marine Policy (2017).
Résumé: Coastal lagoons are important for coastal and marine biodiversity. Nevertheless, they are very sensitive and vulnerable to human impacts, which often result in a decrease of their biodiversity and degradation of their water quality. Considering recent efforts for ecological restoration of coastal lagoons, it appears appropriate to compare the social representations of users of the coastal lagoons and of inhabitants, with ecological diagnoses of biodiversity and water quality. The main question is whether there is congruence between water quality defined by environmental criteria on one hand and the social representations of these issues by lagoon users and local populations on the other hand? How can we explain the social representations of lagoons concerning landscape, water quality and biodiversity? This study was focused on two Mediterranean lagoon areas, i.e., the Palavas lagoon complex (Gulf of Lions) and Biguglia lagoon (Corsica). We have documented these changes of ecosystem states using the criteria of regional monitoring programs that anticipated the implementation of the Water Framework Directive (WFD). Accordingly, both systems have shown bad water quality in the past with recent improvements. For studying the social representations, we conducted 267 surveys with lagoon inhabitants that live close to the lagoons and users of these spaces. In general, most of the residents living close to the lagoons considered that water quality is moderate to good, that biodiversity is good to high and that the current situation is better than in the past. However, some discrepancies between social representations and ecological diagnoses were observed.
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De Wit, R., et al. "Restoration ecology of coastal lagoons: new methods for the prediction of ecological trajectories and economic valuation." Aquatic Conserv: Mar. Freshw. Ecosyst.. 27.1 (2017): 137–157.
Résumé: * Conservation of the seven lagoons of the Palavas complex (southern France) has been severely impaired by nutrient over-enrichment during at least four decades. The effluents of the Montpellier wastewater treatment plant (WWTP) represented the main nutrient input. To improve the water quality of these lagoons, this WWTP was renovated and upgraded and, since the end of 2005, its effluents have been discharged 11 km offshore into the Mediterranean (total investment €150 M). * Possibilities of ecosystem restoration as part of a conservation programme were explored by a focus group of experts. Their tasks were: (i) to evaluate the impact of the reduction of the nutrient input; (ii) if necessary, to design additional measures for an active restoration programme; and (iii) to predict ecosystem trajectories for the different cases. Extension of Magnoliophyta meadows can be taken as a proxy for ecosystem restoration as they favour the increase of several fish (seahorse) and bird (ducks, swans, herons) species, albeit they represent a trade-off for greater flamingos. Additional measures for active ecosystem restoration were only recommended for the most impaired lagoon Méjean, while the least impaired lagoon Ingril is already on a trajectory of spontaneous recovery. * A multiple contingent valuation considering four different management options for the Méjean lagoon was used in a pilot study based on face-to-face interviews with 159 respondents. Three levels of ecosystem restoration were expressed in terms of recovery of Magnoliophyta meadows, including their impact on emblematic fish and avifauna. These were combined with different options for access (status quo, increasing access, increasing access with measures to reduce disturbance). The results show a willingness of local populations to pay per year about €25 for the highest level of ecological restoration, while they were only willing to allocate about €5 for additional footpaths and hides.
Copyright © 2015 John Wiley & Sons, Ltd.
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Fiandrino, A., et al. "Spatial patterns in coastal lagoons related to the hydrodynamics of seawater intrusion." Mar. Pollut. Bull.. 119.1 (2017): 132–144.
Résumé: Marine intrusion was simulated in a choked and in a restricted coastal lagoon by using a 3D-hydrodynamic model. To study the spatiotemporal progression of seawater intrusion and its mixing efficiency with lagoon waters we define Marine Mixed Volume (V-MM) as a new hydrodynamic indicator. Spatial patterns in both lagoons were described by studying the time series and maps of VMM taking into account the meteorological conditions encountered during a water year. The patterns comprised well-mixed zones (WMZ) and physical barrier zones (PBZ) that act as hydrodynamic boundaries. The choked Bages-Sigean lagoon comprises four sub-basins: a PBZ at the inlet, and two WMZ's separated by another PBZ corresponding to a constriction zone. The volumes of the PBZ were 2.1 and 5.4 millions m(3) with characteristic mixing timescale of 68 and 84 days, respectively. The WMZ were 123 and 433 millions m(3) with characteristics mixing timescale of 70 and 39 days, respectively. (C) 2017 Elsevier Ltd. All rights reserved.
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Lavergne, C., et al. "Factors influencing prokaryotes in an intertidal mudflat and the resulting depth gradients." Estuarine, Coastal and Shelf Science. 189 (2017): 74–83.
Résumé: Intertidal mudflats are rich and fluctuating systems in which the upper 20 cm support a high diversity and density of microorganisms that ensure diversified roles. The depth profiles of microbial abundances and activities were measured in an intertidal mudflat (Marennes-Oléron Bay, SW France) at centimeter-scale resolution (0–10 cm below the sediment surface). The aim of the study was to detect microbial stratification patterns within the sediments and the way in which this stratification is shaped by environmental drivers. Two sampling dates, i.e. one in summer and another in winter, were compared. The highest activities of the microbial communities were observed in July in the surface layers (0–1 cm), with a strong decrease of activities with depth. In contrast, in February, low microbial bulk activities were recorded throughout the sediment. In general, prokaryotic abundances and activities were significantly correlated. Variation partitioning analysis suggested a low impact of predation and a mainly bottom-up-controlled prokaryotic community. Hence, in the top layer from the surface to 1–3.5 cm depth, microbial communities were mainly affected by physicochemical variables (i.e. salinity, phosphate and silicate concentrations). Below this zone and at least to 10 cm depth, environmental variables were more stable and prokaryotic activities were low. The transition zone between both layers probably represents a rather smooth gradient (environmental ecocline). The results of our study provide a better understanding of the complex interactions between micro-organisms and their environment in a fluctuating ecosystem such as an intertidal mudflat.
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Manighetti, I., et al. "Vulnerability of intertropical littoral areas." Comptes Rendus Geoscience. 349.6 (2017): 235–237.
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2016 |
DE WIT, R. "Lake La Salada de Chiprana (NE Spain), an Example of an Athalassic Salt Lake in a Cultural Landscape." Intech ed. Lake Sciences and Climate Change. M.Nageeb Rashed, 2016.
Résumé: On a global scale, athalassic inland salt lakes are abundant, albeit restricted to semiarid and arid climates. La Salada de Chiprana is unique in Western Europe, because it is a permanent and relatively deep (up to 5.6 m) hypersaline lake (40–90 g total dissolved salt L–1) since 1700 AD. It forms part of a cultural landscape, which imposes a challenge for management. The aim of this paper is to describe the specific microbial biota and how they interacted with both animals and plant species during the last 25 years. The deeper parts regularly showed salinity stratification with an anoxic sulfide-rich hypolimnion and a bloom of green sulfur bacteria (Prosthecochloris aestuarii and Chlorobium vibrioforme) at the pycnocline. Despite highly eutrophic conditions, often the top water layer is transparent due to top-down control of phytoplankton populations by the brine shrimp, Artemia parthenogenetica. This allows for the development of submerged aquatic vegetation of the endemic foxtail stonewort Lamprothamnium papulosum var. papulosum f. aragonense, and microbial mat communities build by the cyanobacterium Coleofasciculus (Microcoleus) chthonoplastes coexisting with green filamentous nonsulfur bacteria (Chloroflexaceae). The microbial mats show photosynthetically induced precipitation of high-Mg calcite, which by incorporating viruses represents a mechanism for their fossilization.
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Leruste, A., et al. "First steps of ecological restoration in Mediterranean lagoons: Shifts in phytoplankton communities." Estuarine, Coastal and Shelf Science. 180 (2016): 190–203.
Résumé: Along the French Mediterranean coast, a complex of eight lagoons underwent intensive eutrophication over four decades, mainly related to nutrient over-enrichment from continuous sewage discharges. The lagoon complex displayed a wide trophic gradient from mesotrophy to hypertrophy and primary production was dominated by phytoplankton communities. In 2005, the implementation of an 11 km offshore outfall system diverted the treated sewage effluents leading to a drastic reduction of anthropogenic inputs of nitrogen and phosphorus into the lagoons. Time series data have been examined from 2000 to 2013 for physical, chemical and biological (phytoplankton) variables of the water column during the summer period. Since 2006, total nitrogen and phosphorus concentrations as well as chlorophyll biomass strongly decreased revealing an improvement in lagoon water quality. In summertime, the decline in phytoplankton biomass was accompanied by shifts in community structure and composition that could be explained by adopting a functional approach by considering the common functional traits of the main algal groups. These phytoplankton communities were dominated by functional groups of small-sized and fast-growing algae (diatoms, cryptophytes and green algae). The trajectories of summer phytoplankton communities displayed a complex response to changing nutrient loads over time. While diatoms were the major group in 2006 in all the lagoons, the summer phytoplankton composition in hypertrophic lagoons has shifted towards green algae, which are particularly well adapted to summertime conditions. All lagoons showed increasing proportion and occurrence of peridinin-rich dinophytes over time, probably related to their capacity for mixotrophy. The diversity patterns were marked by a strong variability in eutrophic and hypertrophic lagoons whereas phytoplankton community structure reached the highest diversity and stability in mesotrophic lagoons. We observe that during the re-oligotrophication process in coastal lagoons, phytoplankton shows complex trajectories with similarities with those observed in freshwater lake systems.
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Zilius, M., R. de Wit, and M. Bartoli. "Response of sedimentary processes to cyanobacteria loading." Journal of Limnology. 75.2 (2016): 236–247.
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2015 |
De Wit, R., et al. "Viruses Occur Incorporated in Biogenic High-Mg Calcite from Hypersaline Microbial Mats." PLoS ONE. 10.6 (2015): e0130552.
Résumé: Using three different microscopy techniques (epifluorescence, electronic and atomic force microscopy), we showed that high-Mg calcite grains in calcifying microbial mats from the hypersaline lake “La Salada de Chiprana”, Spain, contain viruses with a diameter of 50–80 nm. Energy-dispersive X-ray spectrometer analysis revealed that they contain nitrogen and phosphorus in a molar ratio of ~9, which is typical for viruses. Nucleic acid staining revealed that they contain DNA or RNA. As characteristic for hypersaline environments, the concentrations of free and attached viruses were high (>1010 viruses per g of mat). In addition, we showed that acid treatment (dissolution of calcite) resulted in release of viruses into suspension and estimated that there were ~15 × 109 viruses per g of calcite. We suggest that virus-mineral interactions are one of the possible ways for the formation of nano-sized structures often described as “nanobacteria” and that viruses may play a role in initiating calcification.
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Joux, F., et al. "Methods for Studying Microorganisms in the Environment." Eds. J. - C. Bertrand, et al. Environmental Microbiology: Fundamentals and Applications. Springer Netherlands, 2015. 757–829.
Résumé: The main methods for the study of microorganisms in the environment (water, soil, sediment, biofilms), the different techniques of sampling for measuring biomass, the activities, and the diversity of the microorganisms are presented. To respond to these various issues, techniques as varied as those of flow cytometry, molecular biology, biochemistry, molecular isotopic tools, or electrochemistry are implemented. These different techniques are described with their advantages and disadvantages for different types of biotopes. The question of the isolation, culture, and conservation of microorganisms from the environment are also addressed. Without being exhaustive, this chapter emphasizes the importance of using appropriate and efficient methodological tools to properly explore the still mysterious compartment of microorganisms in the environment.
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Leruste, A., et al. "Selecting an HPLC method for chemotaxonomic analysis of phytoplankton community in Mediterranean coastal lagoons." Transitional Waters Bulletin. 9.1 (2015): 20–41.
Résumé: 1 – Phytoplankton observations are commonly used to contribute to the assessment of aquatic ecosystem health and their trophic status. Compared to other methods, chemotaxonomic analysis based on High Pressure Liquid Chromatography (HPLC) presents many advantages (e.g., rapidity, reproducibility, and capacity to include pigments from all cell sizes), but its use in coastal lagoons studies is still not very common. The method of Wright et al., (1991) recommended by the UNESCO (Jeffrey et al., 1997) and most frequently used for phytoplankton analysis in coastal lagoons, so far, was selected and compared to the more novel method of Hagerthey et al. (2006). 2 – The two methods that differed slightly with respect to their solvent gradients during chromatography (mobile phase) and column (stationary phase), were tested using a pigment mix from DHI Water and Environment comprising 30 different pigments. Extraction methods were tested using replicates of 1l of sub-surface water from the Thau lagoon (South of France), sampled in June 2013. Optimization of the extraction was performed by testing different volumes of solvent (2 to 5 ml), different solvents based on a mix of methanol, acetone, dimethylformamide, water, compared to acetone 90% and pure methanol, as well as different extraction times (10 min to 2 h), and the addition of the ion-pairing agent tetrabutyl ammonium acetate hydroxide (TBAA). 3 – The second method of analysis allowed better separation and resolution of most of the pigments, especially of lutein and zeaxanthin. The early-eluting most polar pigments and the more hydrophobic pigments eluting in the end of the chromatogram (chlorophylls and carotenoids) showed also better separation and peak shapes. 5 mL of the mix of acetone/ methanol/ water (45:45:10) allowed the best extraction of the pigments. The use of TBAA showed negative effects. 4 – For pigment analysis in coastal lagoon, our final protocol used 1 h extraction with 5 mL of acetone/ methanol/ water, and analysis with the gradient from Hagerthey et al. (2006). On our analytical equipment it needed some adjustments. It uses a longer chromatography run and quantified the phytoplankton pigment markers better than the method of Wright et al. (1991).
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Mostajir, B., et al. "Microbial Food Webs in Aquatic and Terrestrial Ecosystems." Eds. J. - C. Bertrand, et al. Environmental Microbiology: Fundamentals and Applications. Springer Netherlands, 2015. 485–509.
Résumé: In microbial food webs, different types of interactions occur between microorganisms themselves and with meio- and macroorganisms. After an historical and general introduction, the biological components of the microbial food webs in the pelagic and benthic marine and lake ecosystems, as well as in the terrestrial ecosystems, are presented. The functioning of the microbial food webs in different ecosystems is illustrated and explained, including the trophic pathways and transfer of matter from microbial food webs toward meio- and macroorganisms of the superior trophic levels, the nutrient recycling in the aquatic environments, and the decomposition of organic matter in soils. Finally, the factors regulating microbial food webs, primarily “top-down” and “bottom-up” controls, are described with a special focus on the role of viruses in the aquatic microbial food webs.
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Poggiale, J. - C., et al. "Modeling in Microbial Ecology." Eds. J. - C. Bertrand, et al. Environmental Microbiology: Fundamentals and Applications. Springer Netherlands, 2015. 847–882.
Résumé: The bases and the principles of modeling in microbial community ecology and biogeochemistry are presented and discussed. Several examples are given. Among them, the fermentation process is largely developed, thus demonstrating how the model allows determining the microbial population growth rate, the death rate, and the maintenance rate. More generally, these models have been used to increase the development of bioenergetic formulations which are presently used in biogeochemical models (Monod, Droop, DEB models). Different types of interactions (competition, predation, and virus–bacteria) are also developed. For each topic, a complete view of the models used in the literature cannot be presented. Consequently, the focus has been done on the demonstration how to build a model instead of providing a long list of existing models. Some recent results in sediment biogeochemistry are provided to illustrate the application of such models.
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2014 |
Narchi, N. E., et al. "Marine ethnobiology a rather neglected area, which can provide an important contribution to ocean and coastal management." Ocean & Coastal Management. 89 (2014): 117–126.
Résumé: Abstract
This report describes marine ethnobiology as it has been presented and discussed under the conference session “Ethnothalassic interactions” organized for the 13th International Congress of Ethnobiology. We define marine ethnobiology as a field within ethnobiology that specifically comprises the study of the relationships of present and past human societies to marine biota and ecosystems. The session stimulated discussion on this emerging field and its contribution to coastal and ocean management, by exchanging experiences on a diverse array of studies within this field that include: co-management of marine protected areas, seascape management, demise, re-discovery and re-implementation of traditional knowledge-based management schemes, history of artisanal shellfish-farming and of the management of artisanal fisheries, medicinal knowledge of algae, as well as the outreach of ethnobiological studies for the conservation of the cultural-ecological heritage in the coastal zone. We here offer the conclusions of the conference session in the form of a longue duree perspective on coastal management that highlights a broad array of human adaptations to coastal environments. We suggest that these adaptations have to be researched and understood in detail in order to incorporate them into broader coastal management strategies in the presence of the severe environmental and political-economical pressures that currently threaten fishing stocks, marine habitats, and the livelihoods of the 2.6 billion people that depend on the oceans as their main source of protein.
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Zilius, M., et al. "Feedback Mechanisms Between Cyanobacterial Blooms, Transient Hypoxia, and Benthic Phosphorus Regeneration in Shallow Coastal Environments." Estuaries and Coasts. 37.3 (2014): 680–694.
Résumé: We investigated the dissolved oxygen metabolism of the Curonian Lagoon (Baltic Sea) to assess the relative contributions of pelagic and benthic processes to the development of transient hypoxic conditions in shallow water habitats. Metabolism measurements along with the remote sensing-derived estimates of spatial variability in chlorophyll a were used to evaluate the risk of hypoxia at the whole lagoon level. Our data demonstrate that cyanobacterial blooms strongly inhibit light penetration, resulting in net heterotrophic conditions in which pelagic oxygen demand exceeds benthic oxygen demand by an order of magnitude. The combination of bloom conditions and reduced vertical mixing during calm periods resulted in oxygen depletion of bottom waters and greater sediment nutrient release. The peak of reactive P regeneration (nearly 30 mu mol m(-2) h(-1)) coincided with oxygen depletion in the water column, and resulted in a marked drop of the inorganic N:P ratio (from > 40 to < 5, as molar). Our results suggest a strong link between cyanobacterial blooms, pelagic respiration, hypoxia, and P regeneration, which acts as a feedback in sustaining algal blooms through internal nutrient cycling. Meteorological data and satellite-derived maps of chlorophyll a were used to show that nearly 70 % of the lagoon surface (approximately 1,000 km(2)) is prone to transient hypoxia development when blooms coincide with low wind speed conditions.
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2013 |
De Wit, R., et al. "Conservation of a permanent hypersaline lake: management options evaluated from decadal variability of Coleofasciculus chthonoplastes microbial mats." Aquatic Conservation-Marine and Freshwater Ecosystems. 23.4 (2013): 532–545.
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Lyons, W. B., et al. "Geochemistry of streams from Byers Peninsula, Livingston Island." Antarctic Science. 25.2 (2013): 181–190.
Résumé: In January and February 2009, a series of water samples were collected from streams on Byers Peninsula. These samples were analysed for major elements and delta O-18 to determine the role of lithology and landscape position on stream geochemistry, and to understand better the hydrology (i.e. residence time of water) of these systems. Precipitation chemistry is enriched in Na+, as are the streams located close to the coast. Streams originating from inland locations have much higher percentages of Ca2+. In contrast, Mg2+ varied little, though streams that are in greater contact with volcanic-derived soils have slightly higher concentrations. Anion percentages varied greatly between streams with SO42- ranging from 5% to 45% of the anion composition. Dissolved Si concentrations as high as 141 mu M were observed. All these data suggest that active chemical weathering is occurring in this region. A time series over 13 days at one stream showed little variation in major element geochemistry. The delta O-18 of precipitation samples collected over this same period varied by similar to 10 parts per thousand while the majority of stream samples varied less than similar to 1.5 parts per thousand. These data indicate that the stream waters represent mixtures of precipitation events, melting snow and water from the subsurface that had gained solutes through chemical weathering.
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Maurice, C. F., et al. "Linking the lytic and lysogenic bacteriophage cycles to environmental conditions, host physiology and their variability in coastal lagoons." Environmental microbiology. 15.9 (2013): 2463–2475.
Résumé: Changes in environmental conditions and prokaryote physiology can strongly affect the dynamics of both the lysogenic and lytic bacteriophage replication cycles in aquatic systems. However, it remains unclear whether it is the nature, amplitude or frequency of these changes that alter the phage replication cycles. We performed an annual survey of three Mediterranean lagoons with contrasting levels of chlorophyll a concentration and salinity to explore how these cues and their variability influence either replication cycle. The lytic cycle was always detected and showed seasonal patterns, whereas the lysogenic cycle was often undetected and highly variable. The lytic cycle was influenced by environmental and prokaryotic physiological cues, increasing with concentrations of dissolved organic carbon, chlorophyll a, and the proportion of respiring cells, and decreasing with the proportion of damaged cells. In contrast, lysogeny was not explained by the magnitude of any environmental or physiological parameter, but increased with the amplitude of change in prokaryote physiology. Our study suggests that both cycles are regulated by distinct factors: the lytic cycle is dependent on environmental parameters and host physiology, while lysogeny is dependent on the variability of prokaryote physiology. This could lead to the contrasting patterns observed between both cycles in aquatic systems.
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Rossi, F., et al. "Spatial distribution and nutritional requirements of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) in a Mediterranean Nanozostera noltii (Hornemann) meadow." Journal of Experimental Marine Biology and Ecology. 440 (2013): 108–115.
Résumé: Sulphur-oxidising endosymbiont-bearing bivalves often inhabit seagrass meadows, where they can control sulphide levels and variably contribute to carbon cycling, by feeding on endosymbiotic bacteria and/or on particulate organic matter from the water column. The patterns of variability in their feeding mode and their spatial distribution within the seagrass meadows are however poorly studied. Seagrass beds form naturally patchy habitats with seagrass-sand edges that may have variable effects on different organisms. The present study aims at understanding differences in feeding mode and abundance of the endosymbiont-bearing bivalve Loripes lacteus (sensu Poli, 1791) as well as the physiological conditions of its endosymbiotic populations between edge and inner portion of meadows of the eelgrass Nanozostera noltii (Hornemann). In July 2010, Loripes specimens were sampled in 4 eelgrass patches at 2 different locations in the Thau lagoon, South of France. There was a clear negative edge effect on the abundance of small individuals of Loripes, while large individuals were homogeneously distributed between edge and inner part of the meadow. Although Loripes isotopic signatures (delta C-13 and delta N-15) were always closer to those of its symbiotic bacteria than to those of suspension-feeding bivalves, eelgrass edge enhanced mixotrophic behaviour of small animals, which assimilated less bacterial carbon and nitrogen at the edge than in the inner part of the eelgrass meadow. No differences related to eelgrass edges were instead found for the bacterial populations harboured by Loripes. Rather, flow cytometry revealed large variability at small spatial scales. Although bacteria were always important for the nutrition of Loripes, these findings showed that seagrass edges may contribute to regulate feeding mode and population structure of Loripes, which may have implications for seagrass functioning. (C) 2012 Elsevier B.V. All rights reserved.
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2012 |
De Wit, R., N. Mazouni, and P. Viaroli. "Preface: Research and Management for the Conservation of Coastal Lagoon Ecosystems, South–North Comparisons." Hydrobiologia. 699.1 (2012): 1–4.
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De Wit, R., et al. "Short-term interactions between phytoplankton and intertidal seagrass vegetation in a coastal lagoon (Bassin d’Arcachon, SW France)." Hydrobiologia. 699.1 (2012): 55–68.
Résumé: We experimentally simulated the temporality of the interactions between intertidal seagrasses and phytoplankton in the context of nutrient enrichment from continental origin. Phytoplankton development was retarded after 1-day exposure to intertidal Zostera noltii Hornemann vegetation samples, with respect to control treatments. This was not explained by resource competition and we hypothesized a direct interference between seagrass leaves and phytoplankton. After separation from the vegetation in 5-day incubations, the final yield of large phytoplankton, mainly diatoms and haptophytes, was determined by nutrient loading. In contrast, Synechococcus -like cells (SYN), phototrophic picoeukaryotes and nanophytoplankton decreased after day 3, most likely due to grazing control. A second experiment was designed to test the pelagos–benthos coupling in more detail. Therefore, we compared the effect of aboveground biomass of Z. noltii alone with the effect of the entire vegetation including the sediment. This experiment did not provide unequivocal support for our initial hypothesis on direct interference competition between Z. noltii leaves and phytoplankton. Surprisingly, we found a spectacular decrease of SYN, phototrophic picoeukaryotes and nanophytoplankton in treatments with Z. noltii vegetation including the sediment, which could be attributed to benthic grazing by suspension feeders.
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Gaertner-Mazouni, N., and R. De Wit. "Exploring new issues for coastal lagoons monitoring and management." Estuarine Coastal and Shelf Science. 114 (2012): 1–6.
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Villeger, S., et al. "Nutrient recycling by coastal macrofauna : intra- versus interspecific differences." Marine Ecology-Progress Series. 452 (2012): 297–303.
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2011 |
Maurice, C. F., et al. "Disentangling the relative influence of bacterioplankton phylogeny and metabolism on lysogeny in reservoirs and lagoons." ISME Journal. 5.5 (2011): 831–842.
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2009 |
De Junet, A., et al. "A multi-tracers analysis of sources and transfers of particulate organic matter in a tropical reservoir (petit saut, french guiana)." River Research and Applications. 25.3 (2009): 253–271.
Résumé: We measured the organic carbon (OC) content, the isotopic composition, the C/N ratios and the photosynthetic pigment composition of suspended matter, sediments, sediments traps and epiphytic and epilithic biofilms at the tropical Sinnamary River system (French Guiana). Our sampling included the mid-stream reservoir lake (Petit Saut) and the estuary on the Atlantic coast. These tracers were complementary and allowed identifying different Sources of particulate organic matter (POM) in the system. We found a delta(13)C-C/N signature of POM close to that of soils and litters collected in the surrounding forest, both for water column and sediment at the upstream station as well as for the sediment in a littoral zone of the reservoir, which thus indicated a terrestrial origin. Plankton communities at the centre of the reservoir were dominated by Chlorophyceae (chlorophyll a Will a), chlorophyll b (Chl b) and lutein) in the oxic epilimnion and by anoxygenic phototrophic bacteria, namely Chlorobiaceae (bacteriochlorophyll d (BChl d) and bacteriochlorophyll c (BCh1 c)) at and below the oxycline (6 m depth). In addition, this planktonic material was slightly (13)C-depleted due to a contribution of methanotrophic bacteria, Phytoplankton and bacterioplankton were the major source of settling material collected in the traps at all depths in the centre of the reservoir. In the traps, POM was subject to intense degradation, as revealed by C/N and isotopic data and by the presence of pheopigments. In the river downstream of the dam, Chl b, lutein, BChl c and d originating from the reservoir progressively decreased downstream its the result of mineralization. At the estuarine mouth, fucoxanthin showed the presence of diatoms and the delta(13)C-C/N signature matched that of POM carried by the Amazonian coastal mobile mud belt. By analysing sedimentation rates in the reservoir and its outflow into the river, we were able to provide a first estimates of POM transfers in this system during the sampling period. Copyright (C) 2008 John Wiley & Sons, Ltd.
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2008 |
de Beer, D., et al. "A microsensor for carbonate ions suitable for microprofiling in freshwater and saline environments." Limnology and Oceanography-Methods. 6 (2008): 532–541.
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De Wit, R. "Microbial diversity in the Bassin d'Arcachon coastal lagoon (SW France)." Hydrobiologia. 611 (2008): 5–15.
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