La Côte-Saint-André, France
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Abonyi A.,University of Pannonia | Leitao M.,Bi Eau | Lancon A.M.,Bi Eau | Padisak J.,University of Pannonia
Hydrobiologia | Year: 2012

The phytoplankton functional group concept is successfully used to assess ecological status in lakes (Q index), and also provides a method for lotic ecosystems (Q (r) index). Here, we examine the Q (r) composition metric to demonstrate local to regional scale human effects on natural distribution of phytoplankton along the River Loire. Distribution of phytoplankton functional groups coupled with chemical and physical parameters are described at whole river scale (19 stations, between March and November 2009). Natural longitudinal changes were reflected by the switch from benthic Pennales (T B) towards meroplanktic greens (J) via unicellular centric diatoms (D/C). While upstream human pressure was mostly associated to species indicating eutrophic, stagnant environments (coda P, M, H1, Y), downstream attenuation of the Q (r) reflected enriched, shallow environments with prolonged residence time (coda J, X2, X1). Occurrence of minimum Q (r) index values were synchronized to late summer, but the longer was the distance from the source, the earlier was the seasonal decrease of Q (r). Increasing downstream co-dominance of codon F evidenced an ascending light availability in summer. The longitudinal distribution of functional groups allowed us to conclude that functional diversity might be able to sign human-affected richness, while simply species diversity does not. © 2012 Springer Science+Business Media B.V.


Yvon-Durocher G.,University of Exeter | Yvon-Durocher G.,Queen Mary, University of London | Allen A.P.,Macquarie University | Cellamare M.,Bi Eau | And 10 more authors.
PLoS Biology | Year: 2015

Phytoplankton are key components of aquatic ecosystems, fixing CO2 from the atmosphere through photosynthesis and supporting secondary production, yet relatively little is known about how future global warming might alter their biodiversity and associated ecosystem functioning. Here, we explore how the structure, function, and biodiversity of a planktonic metacommunity was altered after five years of experimental warming. Our outdoor mesocosm experiment was open to natural dispersal from the regional species pool, allowing us to explore the effects of experimental warming in the context of metacommunity dynamics. Warming of 4°C led to a 67% increase in the species richness of the phytoplankton, more evenly-distributed abundance, and higher rates of gross primary productivity. Warming elevated productivity indirectly, by increasing the biodiversity and biomass of the local phytoplankton communities. Warming also systematically shifted the taxonomic and functional trait composition of the phytoplankton, favoring large, colonial, inedible phytoplankton taxa, suggesting stronger top-down control, mediated by zooplankton grazing played an important role. Overall, our findings suggest that temperature can modulate species coexistence, and through such mechanisms, global warming could, in some cases, increase the species richness and productivity of phytoplankton communities. © 2015 Yvon-Durocher et al.


Borics G.,Center for Ecological Research | Abonyi A.,Bi Eau | Abonyi A.,Hungarian Academy of Sciences | Varbiro G.,Center for Ecological Research | And 2 more authors.
Inland Waters | Year: 2015

Stratification of small temperate lakes of the Carpathian basin was studied. Values of Schmidt stability and Lake Number indicated stable summer stratification. Depending on their depth and wind shelter, the lakes could be characterized by various stratification patterns. A near-linear stratification was observed in the Malom Tisza oxbow where in summer during midday the whole water column belonged to the metalimnion. Mixing of the upper water layer was generated by nocturnal cooling. Stable stratification had pronounced consequences for the vertical distribution of chemical variables and phytoplankton. Concentration of sestonic chlorophyll showed bimodal distribution produced by algae in the upper and purple bacteria in the deeper layers. These results revealed that processes and phenomena associated with deep stratified lakes can be observed in shallow basins. © International Society of Limnology 2015.


Abonyi A.,Bi Eau | Abonyi A.,University of Pannonia | Leitao M.,Bi Eau | Stankovic I.,Central Water Management Laboratory | And 3 more authors.
Ecological Indicators | Year: 2014

Functional groups of phytoplankton make possible various classifications among taxa and this approach has been receiving a growing scientific interest. We compared three frequently used classifications as possible ecological tools in providing river zones along the large, Continental Atlantic River Loire. The different number of functional groups in each classification was synchronized into six clusters using the Self Organizing Map (SOM) method, which clusters (as river zones where relevant) were then compared in their response to geographical location, hydrological and chemical constraints. Our findings demonstrated that all the three classifications might serve as a rational tool, but at different level of understanding. Only approaches based on fine functional resolution in benthic and planctonic diatoms, as well as in cyanobacteria were able to provide reliable river zones at both whole river, and at spatio-temporal scales. Functional groups of these approaches followed different regional patterns in geographical, physical and chemical constraints, and were useful ecological indicators of natural river longitudinal processes, as well as of human impacts such as damming or agriculture. © 2014 The Authors.


Cellamare M.,University Paris Est Creteil | Lancon A.M.,Bi Eau | Leitao M.,Bi Eau | Cerasino L.,Research and Innovation Center | And 2 more authors.
Hydrobiologia | Year: 2015

We explored phytoplankton communities from a functional perspective in two connected but hydro-morphologically distinct basins during the ice-free period in the cold and oligotrophic Lake Tovel, Italy. Despite the absence of dispersal barriers, we expected a clear separation of the phytoplankton communities between basins based on their physical distinctions: a shallow and a deep basin with low and high water residence time, respectively. To investigate seasonal succession and spatiality, taxa were classified according to their functional groups (FGs) and traits (FTs). Relationships between functional classifications and environmental parameters were assessed by non-metric multidimensional scaling integrated with cluster analysis. Clustering of FGs and FTs was complementary and reflected different hydrological conditions of each basin: (i) more stable conditions and higher functional variation across seasons in the deep basin and (ii) less stable conditions and lower functional variation across seasons in the shallow basin. Phytoplankton functional composition evidenced how local conditions selected for corresponding functional attributes adapted to each basin’s environment. These results, together with the presence of rare, cold-tolerant taxa such as Pseudotetraëdriella kamillae and Stephanocostis chantaicus, highlighted the need for long-term phytoplankton studies, and the creation of a FG that includes cold-adapted, oligotrophic taxa. © 2015 Springer International Publishing Switzerland


Minaudo C.,University of Tours | Moatar F.,University of Tours | Meybeck M.,University Pierre and Marie Curie | Curie F.,University of Tours | And 2 more authors.
IAHS-AISH Proceedings and Reports | Year: 2013

The Loire River basin is very sensitive to eutrophication due to its multiple-channel morphology, summer low flows, high water temperatures, and high exposure to nutrient inputs from agriculture and urban sources. The seasonal variation of nutrients and chlorophyll - a from the river headwaters to the estuary (1012 km) was studied by harmonic analysis for three periods between 1981 and 2011. The Upper Loire does not present significant seasonal variations. The eutrophication level of the Middle and Lower Loire, favoured by hydroclimatic conditions, is responsible for significant seasonal amplitude of algal pigments, nutrients and physico-chemical variables. In the Middle Loire, the summer phosphate minimum (15 μg L-1) is controlled by algal uptake, and the summer nitrate minimum (0.8 mg-N L-1) is attributed to algal uptake and denitrification. The 1991 European Directives had an impact on phosphorus levels, but nitrate levels kept increasing slightly, showing a lack of appropriate agro-environmental measures in the Loire River basin. Copyright © 2013 IAHS Press.


Cellamare M.,IRSTEA | de Tezanos Pinto P.,University of Buenos Aires | de Tezanos Pinto P.,CONICET | Leitao M.,Bi Eau | And 3 more authors.
Hydrobiologia | Year: 2013

Functional characteristics play an important role in shaping phytoplankton distributions. This approach can help to explain the success of tropical taxa in temperate ecosystems. We used functional groups (FG) and functional traits (FT) to assess the phytoplankton distribution in five temperate lakes exposed to tropical taxa dispersal. We ran redundancy analyses to assess the relationship between each functional classification and the environment. Both approaches showed similar variance of the phytoplankton biomass and responded to similar environmental variables. The FG approach separated lakes by trophic status (total phosphorus: TP), while the FT approach reflected the lakes' hydromorphology (conductivity, depth, mixing regime). The traits of motility and mixotrophy coincided with low mixing and high light. Tropical taxa were dominant in two lakes, rare in one and absent in two lakes. When dominant, tropical taxa exerted an overwhelming effect on phytoplankton biomass and community composition, and contributed to foam occurrences. The success of tropical taxa in only two lakes seems related to the interplay of their traits (accessory pigments, morphology) and the prevailing environmental filters (low light, deep mixing, and intermediate TP). Their rarity or absence in the other lakes evidences how traits can increase fitness in one environment but not in other. © 2012 Springer Science+Business Media Dordrecht.


Cellamare M.,IRSTEA | Leitao M.,Bi Eau | Coste M.,IRSTEA | Dutartre A.,IRSTEA | Haury J.,Agrocampus Ouest
Hydrobiologia | Year: 2010

In the last decades, numerous exotic species of microalgae have been found in the continental waters of Europe. In three natural shallow lakes located in the southwest of France, several planktonic species typically encountered in tropical areas were observed during 2006 and 2007. The most representative taxa were Planktolyngbya microspira Kom. & Cronb. P. circumcreta (G. S. West) Anagn. & Kom., Cyanodictyon tropicale Senna, Delazari & Sant'Anna and Staurastrum excavatum var. planctonicum Krieg. These species had so far only been reported from African lakes and other tropical areas, but in this study they accounted for up to 58 and 12% of the total abundance and biomass, respectively, during spring and summer. Some of these lakes were studied in the 1970s and only exotic desmids were reported; but at that time, the three cited cyanobacteria were not described yet. Waterfowl are considered as the main dispersers because they migrate over long distances, transporting algae on the feet and feathers or in the digestive tract. In fact, the Aquitaine Region is one of the main bird migration corridors in Europe. Survival of cyanobacteria, diatoms and desmids carried by birds could be possible due to resting stages, sheaths investments or vegetative cells. In addition, global warming may have contributed to the success of these tropical species in temperate lakes. Indeed, minimal temperatures have increased significantly in the Aquitaine region over the last 30 years and could have played a key role in algal survival through winter. © Springer Science+Business Media B.V. 2009.


Stoyneva M.P.,Sofia University | Descy J.-P.,University of Namur | Balague V.,CSIC - Institute of Marine Sciences | Compere P.,Jardin Botanique National de Belgique | And 2 more authors.
Hydrobiologia | Year: 2012

The coccal unicellular green algal genus Tetraëdron Kütz. ex Korshikov, which can be easily identified by its typical polygonal shape, is a common member of freshwater plankton and metaphyton, frequently observed in lowland temperate and tropical waters. During the analysis of samples from tropical Lake Kivu (Eastern Africa), we found an interesting "lemon-shaped" alga, which, after observations in light microscope and scanning electron microscope, had been listed as Tetraëdron sp. Isolation in pure culture allowed a deeper study on morphology at different stages of the life cycle and the partial sequencing of the 18S rDNA. The results from the different combined approaches confirmed that it belongs to the species Tetraëdronminimum (A. Braun) Hansg. The unusual "lemon-shaped" forms predominant in Lake Kivu are young stages of the life cycle. This study contributes to the knowledge of the morphological variability, reproduction, and resting stages of T. minimum and discusses the reasons for the dominance of such unusual shape found in Lake Kivu, a lake strongly impacted by human activities as resulted by the large-scale biomanipulation following the introduction of the "Tanganyika sardine," Limnothrissa miodon (Boulenger, 1906), at the end of the 1950s. © 2012 Springer Science+Business Media B.V.

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