Station Biologique de la Tour du Valat

La Tour-du-Pin, France

Station Biologique de la Tour du Valat

La Tour-du-Pin, France
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Geertz-Hansen O.,Copenhagen University | Montes C.,Autonomous University of Madrid | Duarte C.M.,CSIC - Mediterranean Institute for Advanced Studies | Duarte C.M.,University of Western Australia | And 3 more authors.
Biogeosciences | Year: 2011

The metabolic balance of the open waters supporting submerged macrophytes of the Doñana marsh (SW Spain) was investigated in spring, when community production is highest. The marsh community (benthic + pelagic) was net autotrophic with net community production rates averaging 0.61 g C m -2 d-1, and gross production rates exceeding community respiration rates by, on average, 43%. Net community production increased greatly with increasing irradiance, with the threshold irradiance for communities to become net autotrophic ranging from 42 to 255 μE m -2 s-1, with net heterotrophic at lower irradiance. Examination of the contributions of the benthic and the pelagic compartments showed the pelagic compartment to be strongly heterotrophic (average P/R ratio Combining double low line 0.27), indicating that the metabolism of the pelagic compartment is highly subsidised by excess organic carbon produced in the strongly autotrophic benthic compartment (average P/R Combining double low line 1.58). © 2011 Author(s).


Pujolar J.M.,University of Padua | Vincenzi S.,University of Parma | Zane L.,University of Padua | Jesensek D.,Tolmin Angling Association | And 2 more authors.
PLoS ONE | Year: 2011

A changing global climate can threaten the diversity of species and ecosystems. We explore the consequences of catastrophic disturbances in determining the evolutionary and demographic histories of secluded marble trout populations in Slovenian streams subjected to weather extremes, in particular recurrent flash floods and debris flows causing massive mortalities. Using microsatellite data, a pattern of extreme genetic differentiation was found among populations (global F ST of 0.716), which exceeds the highest values reported in freshwater fish. All locations showed low levels of genetic diversity as evidenced by low heterozygosities and a mean of only 2 alleles per locus, with few or no rare alleles. Many loci showed a discontinuous allele distribution, with missing alleles across the allele size range, suggestive of a population contraction. Accordingly, bottleneck episodes were inferred for all samples with a reduction in population size of 3-4 orders of magnitude. The reduced level of genetic diversity observed in all populations implies a strong impact of genetic drift, and suggests that along with limited gene flow, genetic differentiation might have been exacerbated by recurrent mortalities likely caused by flash flood and debris flows. Due to its low evolutionary potential the species might fail to cope with an intensification and altered frequency of flash flood events predicted to occur with climate change. © 2011 Pujolar et al.


Martino A.,Ecolab | Syvaranta J.,Ecolab | Syvaranta J.,Leibniz Institute of Freshwater Ecology and Inland Fisheries | Crivelli A.,Station biologique de la Tour du Valat | And 2 more authors.
Aquatic Conservation: Marine and Freshwater Ecosystems | Year: 2011

European eel (Anguilla anguilla) is recognized as a critically endangered species in the northern hemisphere. Threats such as overfishing or pollution are well known as risks for eel populations. However, much less is known about the impact of introduced fish on European eels. In particular, introduced large-bodied predators could become new predators to eels. The potential impact of European catfish (Silurus glanis L) on an eel population in the Camargue, southern France was studied using a combination of stable isotope and gut content analyses. Only large-bodied catfish (>500mm) can consume numerous fish prey. However, catfish mostly consumed crayfish (Procambarus clarkii), these prey items being found in 79% of the guts of the largest individuals. Eel was absent from the dissected catfish guts. A mixing model based on Bayesian inference revealed that catfish diet included only 5% (0-8.5%) of marine sources (both eel and mullet). While local economic interests prompted ecological studies to assess whether catfish exerted a new and strong predatory pressure on eel, this study found that European catfish behaved as an opportunistic omnivore, and as such was not a direct threat as a predator on eel populations in the Camargue. © 2011 John Wiley & Sons, Ltd.


Berrebi P.,Montpellier University | Jesensek D.,Fisheries Association Tolmin | Crivelli A.J.,Station Biologique de la Tour du Valat
Hydrobiologia | Year: 2016

The endemic marble trout, Salmo trutta marmoratus, suffered massive stocking with brown trout in Slovenia and Italy. In the Soča River (Slovenia) long-term surveys have evidenced Danubian and Atlantic introgressions. The observation of discrepancies between introgression frequencies when using morphology, mitochondrial sequences, allozymes, or microsatellites markers led to reanalyze the hybrid population of the Soča River. New analyses on diachronic samples of the Soča hybrid populations was performed, genotyping partly the same individuals on one diagnostic allozyme (LDH-C1*), eight microsatellite, and one mitochondrial loci. The confirmed discrepancies led to interpret the anomaly as the consequence of ancient natural immigration of Danubian trout by rivers captures together with stocking with Atlantic domestic trout. Management consequences are discussed because the natural Soča inhabitant which was thought to be a pure marble trout should be now changed into a natural hybrid lineage accepting few Danubian alleles. © 2016 Springer International Publishing Switzerland


Vincenzi S.,University of Parma | Vincenzi S.,University of California at Santa Cruz | Crivelli A.J.,Station Biologique de la Tour du Valat | Giske J.,University of Bergen | And 3 more authors.
Oecologia | Year: 2012

Optimal life histories in a fluctuating environment are likely to differ from those that are optimal in a constant environment, but we have little understanding of the consequences of bounded fluctuations versus episodic massive mortality events. Catastrophic disturbances, such as floods, droughts, landslides and fires, substantially alter the population dynamics of affected populations, but little has been done to investigate how catastrophes may act as a selective agent for life-history traits. We use an individual-based model of population dynamics of the stream-dwelling salmonid marble trout (Salmo marmoratus) to investigate how trade-offs between the growth and mortality of individuals and density-dependent body growth can lead to the maintenance of a wide or narrow range of individual variation in body growth rates in environments that are constant (i. e., only demographic stochasticity), variable (i. e., environmental stochasticity), or variable with catastrophic events that cause massive mortalities (e. g., flash floods). We find that occasional episodes of massive mortality can substantially reduce persistent variability in individual growth rates. Lowering the population density reduces density dependence and allows for higher fitness of more opportunistic strategies (rapid growth and early maturation) during the recovery period. © 2011 Springer-Verlag.


Vincenzi S.,University of Parma | Crivelli A.J.,Station Biologique de la Tour du Valat | Jesensek D.,Tolmin Angling Association | De Leo G.A.,University of Parma
Ecology of Freshwater Fish | Year: 2010

Density-dependent body growth has often been observed in freshwater salmonid populations. Several studies suggest this compensatory pattern as a potential mechanism of population regulation. The choice of the spatial scale is important for the detection of density-dependent growth, as study areas need to be of the appropriate size to capture the density of conspecifics actually experienced by individuals over the preceding growth period. Here, we used four marble trout (Salmo marmoratus) populations (Gatsnik, Gorska, Huda and Zakojska) living in Slovenian stream to study the relationships between early density of marble trout and subsequent body growth. As streams are divided in sectors delimited by natural barriers that prevent or strongly limit movement of individuals, we tested the relationship between early density and body size through the lifetime at two spatial scales, that is, sector level (for Gatsnik and Zakojska) and whole stream level (the four populations were pooled). Sector length in Gatsnik and Zakojska ranged from 113 to 516 m. At both sector and whole stream level, temporal data were pooled. Growth declined significantly with increasing density both at the sector and whole stream levels, and the density-dependent relationship was described by negative power curves. However, at the sector level the density-dependent pattern was stronger in Gatsnik, a stream in which fish could move across sectors, than in Zakojska, where upstream movement across sectors is prevented by waterfalls. © 2010 John Wiley & Sons A/S.


Vincenzi S.,University of Parma | Crivelli A.J.,Station Biologique de la Tour du Valat | Jesensek D.,Tolmin Angling Association | De Leo G.A.,University of Parma
Ecology of Freshwater Fish | Year: 2010

The role of density-dependent individual growth in the recruitment dynamics of fish populations has rarely been analysed in a quantitative framework. Variations of mean size of juveniles in response to changes in population densities have frequently been observed in salmonids and it has been shown that body-size differences at the juvenile stage can persist through the sub-adult and adult stage. As fecundity and sexual maturation are often a function of body size, inter-cohort variations in individual growth may ultimately affect the reproductive output and, consequently, the amount of yearly recruitment. Here, we present a simulation analysis investigating the effects of density-dependent growth on the reproductive output and, ultimately, on the population dynamics of stream-dwelling salmonids. The demographic model used for the numerical analysis was parameterised using marble trout Salmo marmoratus as a reference species and explicitly accounted for the occurrence of major floods events causing the population to collapse to very low densities. Our simulations showed that density-dependent individual growth is a powerful mechanism to foster population resilience through compensatory recruitment. In addition, we argue that density-dependent growth also helps regulate recruitment at high population densities. We show that even slight variations in the growth trajectories of fish substantially affect the size and the dynamics of the population. © 2010 John Wiley & Sons A/S.


Vincenzi S.,University of California at Santa Cruz | Crivelli A.J.,Station Biologique de la Tour du Valat | Jesensek D.,Tolmin Angling Association | de Leo G.A.,University of Parma
Reviews in Fish Biology and Fisheries | Year: 2012

Translocation programs are a common strategy to increase the number of viable populations of threatened freshwater fishes. Yet, only in a minority of cases the success or failure of translocations has been assessed through a quantitative analysis of demographic traits, compensatory responses, life-histories and population dynamics of the threatened species. A paradigmatic case a translocation program combining both management- and research-oriented activities is represented by the Marble Trout Conservation Program, which started in 1993 in the upper reaches of the Soca, Idirjca and Baca river basins (Slovenia) for the conservation of stream-dwelling marble trout Salmo marmoratus. In order to enhance the viability of the species, two new populations were created in 1996 by stocking 500 marble trout aged 1+ in previously fishless streams (Gorska and Zakojska) within the core habitat of the species. The new populations have been systematically monitored for 15 years by individually tagging and sampling marble trout. Our analyses show that deterministic extinction of marble trout populations are unlikely and that high-magnitude environmental stochasticity (i.e., severe floods) is the only main cause of local population extinction, despite the high resilience to flood-induced massive mortalities exhibited by marble trout through compensatory mechanisms (e.g., relaxation of density-dependent body growth and survival at low densities). Fishless headwaters, probably characterized by a history of recurrent severe floods, should not be considered as candidate sites for the creation of new populations. Fewer individuals than originally reintroduced (i.e., 500 fish aged 1+ in each stream) might be sufficient to establish viable populations, since compensatory mechanisms are likely to regulate population size around stream carrying capacity in a few years. Besides enhancing the species viability, translocation programs can provide an excellent framework for the estimation of ecological traits (e.g., life-histories, demography, population dynamics etc.), identify potential vulnerabilities and thus guide well-formed management actions for the threatened species. © 2011 Springer Science+Business Media B.V.


Lefebvre F.,Station Biologique de la Tour du Valat | Fazio G.,47 rue des Trois Rois | Mounaix B.,Fish Pass | Mounaix B.,Institute Of Lelevage | Crivelli A.J.,Station Biologique de la Tour du Valat
Proceedings of the Royal Society B: Biological Sciences | Year: 2013

Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because the epidemiological history of field-sampled hosts is often unknown. In this study, we used an internal marker of the parasite pressure on individual hosts to evaluate the costs of parasitism with respect to host body condition, size increase and reproductive potential of field-collected animals for which we also determined individual age. In our investigated system, the European eel Anguilla anguilla and the parasitic invader Anguillicoloides crassus, high virulence and severe impacts are expected because the host lacks an adaptive immune response. We demonstrated a nonlinear relationship between the severity of damage to the affected organ (i.e. the swimbladder, our internal marker) and parasite abundance and biomass, thus showing that the use of classical epidemiological parameters was not relevant here. Surprisingly, we found that the most severely affected eels (with damaged swimbladder) had greater body length and mass (+11% and +41%, respectively), than unaffected eels of same age. We discuss mechanisms that could explain this finding and other counterintuitive results in this host-parasite system, and highlight the likely importance of host panmixia in generating great inter-individual variability in growth potential and infection risk. Under that scenario, the most active foragers would not only have the greatest size increase, but also the highest probability of becoming repeatedly infected-via trophic parasite transmission-during their continental life. © 2013 The Author(s) Published by the Royal Society. All rights reserved.


Lefebvre F.,Station Biologique de la Tour du Valat
Proceedings. Biological sciences / The Royal Society | Year: 2013

Quantifying the fitness cost that parasites impose on wild hosts is a challenging task, because the epidemiological history of field-sampled hosts is often unknown. In this study, we used an internal marker of the parasite pressure on individual hosts to evaluate the costs of parasitism with respect to host body condition, size increase and reproductive potential of field-collected animals for which we also determined individual age. In our investigated system, the European eel Anguilla anguilla and the parasitic invader Anguillicoloides crassus, high virulence and severe impacts are expected because the host lacks an adaptive immune response. We demonstrated a nonlinear relationship between the severity of damage to the affected organ (i.e. the swimbladder, our internal marker) and parasite abundance and biomass, thus showing that the use of classical epidemiological parameters was not relevant here. Surprisingly, we found that the most severely affected eels (with damaged swimbladder) had greater body length and mass (+11% and +41%, respectively), than unaffected eels of same age. We discuss mechanisms that could explain this finding and other counterintuitive results in this host-parasite system, and highlight the likely importance of host panmixia in generating great inter-individual variability in growth potential and infection risk. Under that scenario, the most active foragers would not only have the greatest size increase, but also the highest probability of becoming repeatedly infected-via trophic parasite transmission-during their continental life.

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