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Abstract: δ13C and δ15N values in crustacean taxa were measured once a month in two alpine lakes over a 2-year period in order to address seasonal changes in the isotope composition of the zooplankton. Daphnia sp. was used as the ‘pelagic baseline’ (i.e. primary sources fueling the pelagic food web), as it exhibited the lowest δ13C and δ15N values among the crustacean taxa. Seasonal changes resulting from modifications in the trophic position of other crustacean taxa were assessed by comparing their seasonal δ13C and δ15N values to those of Daphnia sp. Baseline modifications were addressed by relating them to physical, chemical and biological changes in the epilimnion. In Lake Geneva, all the crustacean taxa rely on the same carbon source and occupy relative trophic positions that display no major changes over time. In contrast, in Lake Annecy, the crustacean food web was found to be much more complex. The crustacean taxa apparently obtained their carbon from differing primary sources and their relative trophic positions changed during the year. This study raises the question of the ambiguity of the pelagic baseline concept when applied to zooplankton trophic studies. [Copyright &y& Elsevier]

The scales of whitefish Coregonus lavaretus were used in place of dorsal muscle, which necessitates killing the fish, to study food webs from the δ13C and δ15N isotopic ratios in the organic fraction. As scales are composed of both organic and calcified fractions, a protocol for scale decalcification was first devised. The δ13C and δ15N values of the decalcified scales were then shown to be closely correlated to those of the dorsal muscle, demonstrating that scales could be used in place of muscle to study food webs. Changes in the δ13C of whitefish were determined from a scale collection that extended over the period during which the trophic state of Lake Geneva was recovering. [ABSTRACT FROM AUTHOR]

Rationale: Sequential analysis of otolith oxygen isotope (δ(18) O(oto) ) values was performed by classical mechanical microdrilling and dual inlet mass spectrometry to infer the timing of growth checks in pike (Esox lucius) scales from Lake Annecy (France). It indicated that the first check on scales occurs before the first winter of life of the fish., Methods: Eleven fish caught in February and June 2008 were studied. Intra-individual isotopic profiles exhibit cyclic variations that are consistent with that of modeled δ(18) O(oto) values using variations in epilimnion temperature and otolith-specific isotope fractionation equations. The positions of growth checks on scales were compared with the periodic variations of δ(18) O(oto) values on otolith radii using an allometric relationship., Results: All individuals presented at least one check deposited before the first winter. Deposition of some checks might be linked to a shift in fish diet or habitat or to catch-and-release induced stress., Conclusions: Although coupling between sequential analysis of δ(18) O(oto) values and observation of scale growth features has been shown to be useful, there are limitations in the methodology, especially for the growth-attenuated region of otoliths associated with older ages., (Copyright © 2012 John Wiley & Sons, Ltd.)

1. A recurrent question in ecology is the influence of environmental factors, particularly nutrients and climatic variables, on community structure and functioning, and their interaction with internal community processes (e.g. competition). 2. Perialpine lakes have been subject to two main kinds of human-induced changes over the last 50 years: eutrophication-reoligotrophication, represented by lake-specific changes in total phosphorus concentration (TP), and long-term global climatic change, captured by average winter temperature (AWT). 3. Changes in fish communities (abundance of seven species from fishery data) in 11 Perialpine lakes during 31 years (1970-2000) were investigated in relation to variation in TP and AWT using models incorporating the effects of fish maturation age, and potentially discriminating effects on adult survival and recruitment. 4. We show that phosphorus concentration affects fish abundance in species-specific ways. These effects are mediated by recruitment rather than by adult survival. Phosphorus effects are probably modulated by interspecific interactions, as increasing TP enhances total community biomass, which in turn is either positively or negatively associated with species abundance depending on species position in trophic chains. 5. Climatic change has very little effect on fish abundances, which is not consistent with the prediction of larger changes in species near their southern distribution boundary. 6. We propose several hypotheses to account for those findings, and place our study in the wider framework of community ecology.

Most regions in the tropics undergo high seasonal precipitation that produces cyclic patterns of riverine discharge, resulting in periods characterized by low and high water levels. Many chemical and bio-logical factors are affected by this hydrologic seasonality, and it therefore appeared to be very likely that aquatic food webs would also differ during the low and high water periods. Available carbon sources for fish are thought to be less varied during low water periods, but flooding during high water periods could bring fish into contact with a greater abundance and diversity of food sources such as terrestrial plants or the biofilms that grow on submerged terrestrial plants. At low water levels, higher fish densities may lead to more piscivory and less omnivory when compared with the high water periods. Therefore, trophic links within the fish communities may then be modified by water level changes in tropical reservoirs. To address this prediction, we performed stable isotope analyses of the most common species in Sélingué and Manantali, two large reservoirs in Mali (West Africa). Allochthonous and littoral carbon sources were shown to support fish production to a significant extent, even during low water periods. However, the allochthonous or littoral carbon contributions that sustained the top-predators production were indeed greater during the high water periods as expected. The expected higher omnivory in the high water period might have shortened the food chain when compared with the low water period. Some carnivorous fish species were shown to feed at lower trophic levels during high water periods in both reservoirs, but this was not a general pattern. Flooding did not, therefore, necessarily result in a shorter food chain when water levels were high.

The genetic structure of the most abundant species in the genus Eubothrium, E. crassum and E. salvelini, was studied by allozyme analysis in order to provide a consistent diagnosis for these morphologically similar species, as well as to assess their genetic relatedness. The proportion of fixed allelic differences (56.3%, 9 of 16 loci) between the species falls within the range accepted for valid species. A strict host specificity of E. crassum and E. salvelini for their typical host (lake trout, Arctic charr, respectively) was found in the French localities examined (Lake Annecy, Lake Bourget). For E. salvelini, polymorphism with the established allelic profile was found in the acid phosphatase (ACP) system. No significant deviation from the Hardy-Weinberg equilibrium expectations for ACP were found in either of the E. salvelini populations, which suggests predominantly cross-fertilization of these hermaphrodites. Analysis of the standardized variance in allelic frequencies demonstrated almost no among population differentiation (estimator theta of Fst = -0.03) between E. salvelini populations., (Copyright 2004 Springer-Verlag)

Measurements of organochlorine [polychlorinated biphenyls (PCBs) and dichloro-diphenyl-dichloroethylene (DDE)] and Hg concentrations and nitrogen and carbon stable isotopic compositions (delta15N and delta13C) were performed on 63 Arctic char (Salvelinus alpinus) from Lake Geneva. Fish exhibited a high interindividual variablity in pollutant concentrations. Since the accumulation of such persistent contaminants is obtained from food, the co-occurrence of dietary differentiation leading to the contaminant interindividual variability was suspected. delta15N and delta13C were used for assessing trophic position and food source differences among Arctic char. The low ranges of delta15N and delta13C could not explain the interindividual variability in pollutant concentrations. The lack of relation between delta15N and contaminant concentration did not suggest a trophic level biomagnification of PCB, DDE, and Hg. Lake Geneva spatial variability in pollutants may be an important factor of variability within the Arctic char population. The bioaccumulation pattern occurring for Hg was not apparent for PCB and DDE. Organochlorines are hydrophobic contaminants, and their bioaccumulation pattern may be masked by seasonal variations in fish lipid content.

The internal transcribed spacers (ITS-1 and ITS-2) and 5.8S subunit of the ribosomal RNA gene of Eubothrium crassum and Eubothrium salvelini, cestode parasites of salmonid fish, were sequenced and compared. The lengths and GC contents of the regions sequenced were 1119 bp and 50.1% for E. crassum, and 1117 bp and 50.5% for E. salvelini, respectively. Sequence alignment and comparison of both taxa showed 97.9% similarity. Within the ITS-1 and ITS-2 of both species, the restriction enzymes MspI and Bsh1236I possessed different cleavage sites and could be employed for rapid differentiation of both species of Eubothrium by PCR-RFLP.