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Angers, France

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.

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.

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

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.

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.

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