Trophic Ecology

Discrimination between farmed and free-living invasive salmonids in Chilean Patagonia using stable isotope analysis

by Carlos Garcia de Leaniz

Schröder,V.; Garcia de Leaniz,C.(2011). Biological Invasions 13: 203-213
DOI 10.1007/s10530-010-9802-z

In Chilean Patagonia relatively pristine aquatic environments are being modified by the introduction of exotic... more In Chilean Patagonia relatively pristine aquatic environments are being modified by the introduction of exotic salmonids, initially through their deliberate release for sport fishing since the early 20th century, and more recently via the accidental escape from fish farms. There is therefore a need to reliably distinguish between naturally reproducing and fugitive salmonids associated with the Chilean salmonid farming industry, the second largest in the world. We tested the ability of stable isotope analysis (SIA) and analysis of scale growth profiles to discriminate between farmed and free-living salmonids sampled around the Island of Chiloé. Juvenile Atlantic salmon (Salmo salar) and rainbow trout (Oncorhynchus mykiss) from aquaculture facilities were significantly more enriched in ä15N and lipid-corrected ä13C than river-caught individuals. Scale growth slopes during the first year in freshwater were significantly higher in farmed than in wild-caught rainbow trout, indicating faster somatic growth under hatchery conditions. Stable isotopes analysis classified 94% of juvenile Atlantic salmon and rainbow trout to their correct farm or free-living groups. Our results, therefore, can help to elucidate the origin and spread of exotic invasive salmonids in Chile, and address one of the biggest threats to native freshwater fishes in Patagonia and other temperate zones of the Southern Hemisphere. Keywords: stable isotope analysis, invasive species, salmonids, aquaculture

Population-level metrics of trophic structure based on stable isotopes and their application to invasion ecology

by Andrew Jackson

Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric... more Biological invasions are a significant driver of human-induced global change and many ecosystems sustain sympatric invaders. Interactions occurring among these invaders have important implications for ecosystem structure and functioning, yet they are poorly understood. Here we apply newly developed metrics derived from stable isotope data to provide quantitative measures of trophic diversity within populations or species. We then use these to test the hypothesis that sympatric invaders belonging to the same functional feeding group occupy a smaller isotopic niche than their allopatric counterparts. Two introduced, globally important, benthic omnivores, Louisiana swamp crayfish (Procambarus clarkii) and carp (Cyprinus carpio), are sympatric in Lake Naivasha, Kenya. We applied our metrics to an 8-year data set encompassing the establishment of carp in the lake. We found a strong asymmetric interaction between the two invasive populations, as indicated by inverse correlations between carp abundance and measures of crayfish trophic diversity. Lack of isotopic niche overlap between carp and crayfish in the majority of years indicated a predominantly indirect interaction. We suggest that carp-induced habitat alteration reduced the diversity of crayfish prey, resulting in a reduction in the dietary niche of crayfish. Stable isotopes provide an integrated signal of diet over space and time, offering an appropriate scale for the study of population niches, but few isotope studies have retained the often insightful information revealed by variability among individuals in isotope values. Our population metrics incorporate such variation, are robust to the vagaries of sample size and are a useful additional tool to reveal subtle dietary interactions among species. Although we have demonstrated their applicability specifically using a detailed temporal dataset of species invasion in a lake, they have a wide array of potential ecological applications.

Modelling trophic flows in ecosystems to assess the efficiency of marine protected area (MPA), a case study on the coast of Sénégal

by Luis Tito de Morais

Colléter, M., Gascuel, D., Ecoutin, J.-M. & Tito de Morais, L. (2012). Modelling trophic flows in ecosystems to assess the efficiency of marine protected area (MPA), a case study on the coast of Sénégal. Ecological Modelling, 232, 1–13.

Marine protected areas (MPAs) are now viewed as an efficient tool to fight against the global deterioration of... more Marine protected areas (MPAs) are now viewed as an efficient tool to fight against the global deterioration of habitats and fish populations. However their efficiency and effects on the whole trophic network are little known. Based on the Bolong de Bamboung (Sénégal) case study, the objective of this study is to assess the impact of a MPA on the entire trophic network using trophodynamic models. This estuarine small MPA is scientifically surveyed since 2003, one year before the closure of the fishery. Using the resulting dataset, we calculated time series of abundance indices and constructed two Ecopath mass-balanced models for the year 2003 (fished) and the 2006–2008 period (unfished). Using EcoTroph, an ecosystem trophic-level based model, we compared the two periods and simulated a closure of the fishery starting from 2003 to assess the effect of the MPA. We observed a rather constant total biomass, but a biomass increase by a 2.5 factor in predators and a decrease by a 1.7 factor in their preys. Simulations showed that the increase in predators was too important to only being a direct consequence of the removal of the fishing mortality and a local production. This highlighted the role of the MPA as a refuge or a foraging arena for some predator species. What's more, the decrease of the preys, corresponding to pelagic species, was very important and couldn’t be explained only by an increase of the predation plus a release of the fishing pressure. This indicated other possible effects as environmental and behavioural ones, in addition of a direct MPA effect. Sensitivity testing and a comparison with another nearby similar but fished area, the Bolong de Sangako, validated the same global conclusion. We concluded that the fishing closure had direct effects but also indirect ones likely due to fish behaviour and environment, and that trophodynamic models are useful tools to analyse MPA effects on the whole trophic network.

On the importance of body size in the colonisation of ephemeral resource patches by vagile consumers

by giorgio mancinelli

… effects of acidification and competition on the feeding preference of a freshwater macroinvertebrate, Asellus aquaticus (Crustacea: Isopoda): a laboratory experiment

by giorgio mancinelli

Cascading effects of predatory fish exclusion on the detritus-based food web of a lake littoral zone (Lake Vico, central Italy)

by giorgio mancinelli

Temperature-associated population diversity in salmon confers benefits to mobile consumers

by Jonathan Armstrong

Cassemiro etal 2007 - Cichlidae _ Ecology of Freshwater Fish

by Fernanda Cassemiro

Persistent predator–prey dynamics revealed by mass extinction

by Lauren Sallan

Differential response of ants to nutrient addition in a tropical Brown Food Web

by Justine Jacquemin

Étude du régime alimentaire de deux espèces de Cichlidae en situation contrastée dans un estuaire tropical inverse d’Afrique de l’Ouest (Casamance, Sénégal)

by Luis Tito de Morais

Ndour, I., Le Loc’h, F., Thiaw, O.T., Ecoutin, J.M., Laë, R., Raffray, J., Sadio, O., Tito de Morais, L., 2011. Étude du régime alimentaire de deux espèces de Cichlidae en situation contrastée dans un estuaire tropical inverse d’Afrique de l’Ouest (Casamance, Sénégal). J. Sci. Halieut. Aquat. 4, 120-133.

Le barrage anti-sel de Maka a été érigé en 1998 sur le fleuve Casamance (Sénégal) afin de rétablir les conditions... more Le barrage anti-sel de Maka a été érigé en 1998 sur le fleuve Casamance (Sénégal) afin de rétablir les conditions dulçaquicoles au profit de l’activité rizicole des populations locales. Il sépare deux environnements de salinité contrasté : une partie aval salée sous influence de l’estuaire inverse et une partie amont d’eau douce. L’étude comparative des régimes alimentaires de deux Cichlidae Sarotherodon melanotheron heudelotii et Tilapia guineensis vivant de part et d’autre du barrage anti-sel de Maka a été effectuée sur la base d’échantillonnages sur trois périodes différentes en 2006 et 2007 : une saison humide chaude (octobre), une saison sèche froide (février) et une saison sèche chaude (mai). Les régimes alimentaires des deux espèces sont abordés par une méthode classique d’analyse des contenus stomacaux en notant les occurrences des proies. Comparées aux populations de S. m. heudelotii et de T. guineensis qui vivent en amont du barrage, celles vivant en aval du barrage présentent des occurrences de proies plus importantes. S. m. heudelotii tend à ingérer d’avantage de débris végétaux au détriment de la vase lorsque la salinité devient élevée. Par contre, T. guineensis qui dispose d’un spectre trophique plus large, tend à consommer plus de vase (bivalves) que de débris végétaux, lorsque la salinité augmente. La comparaison des régimes alimentaires de ces deux Cichlidae de part et d’autre du barrage, montre une évolution de leurs régimes alimentaires en fonction des conditions environnementales.

Trophic Niche Variation and Individual Specialization in Hypsiboas pulchellus (Duméril and Bibron, 1841)(Anura, Hylidae) from Uruguay

by Raul Maneyro

Environmental and Seasonal Variation In the Diet of Elachistocleis Bicolor (Guérin-Méneville 1838)(Anura: Microhylidae) From Northern Uruguay

by Raul Maneyro

Temporal and spatial changes in the diet of Hyla pulchella (Anura, Hylidae) in southern Uruguay

by Raul Maneyro

Diet of four sympatric anuran species in a temperate environment

by Raul Maneyro

Trophic ecology of a taxocenosis of mediterranean Lacertidae

by César J. Pollo

Co-authored with V. Perez-Mellado

Ecologia Mediterranea XIV (3/4): 131-147 (1988)

Influence of habitat, trophic ecology and lipids on, and spatial trends of, organochlorine contaminants in Arctic marine invertebrates

by Jean-Marc Gagnon

Aaron T. Fisk, Paul F. Hoekstra, Jean-Marc Gagnon, Jason Duffe,
Ross J. Norstrom, Keith A. Hobson, Michael Kwan, Derek C. G. Muir
MARINE ECOLOGY PROGRESS SERIES Vol. 262: 201–214, 2003

Organochlorine contaminants (OCs) and stable isotopes of carbon (δ13C) and nitrogen (δ15N) were determined in 7... more Organochlorine contaminants (OCs) and stable isotopes of carbon (δ13C) and nitrogen (δ15N) were determined in 7 benthic and 7 pelagic marine invertebrate species from the North American
Arctic to identify factors influencing OC concentrations. Values of δ13C separated benthic (enriched in 13C) from pelagic species and δ15N values gave a logical approximation of trophic level
(TL). With few exceptions, OC concentrations in invertebrates were low (most were <5 ng g–1 wet wt) relative to the same or similar species in temperate waters and in the range expected for lower TL
Arctic organisms. Polychlorinated biphenyls (PCBs) were the predominant OC group and lower chlorinated PCB congeners and hexachlorocyclohexane (HCH) isomers were the most common individual OCs in most species. Relatively higher levels of PCBs and high proportions of highly chlorinated PCB congeners were found in a small number of the pelecypod samples (Mytilus edulis and Mya
truncata), suggesting that local harbors and communities can be point sources of PCBs in the Arctic. The OC concentrations (wet wt) varied by up to 2 orders of magnitude among species and were more variable among the benthic invertebrates. Lipid content, δ13C and δ15N were significant variables related to OC concentration, but differences among species remained after accounting for these
variables. Scavenging, high TL, high lipid content and local point sources can all contribute to higher OC concentrations in Arctic marine invertebrates.

A wolf in sheep’s clothing: carnivory in dominant sea urchins in the Mediterranean

by Owen S. Wangensteen

Owen S. Wangensteen, Xavier Turon, Alex García-Cisneros, Mireia Recasens, Javier Romero, Creu Palacín
Mar Ecol Prog Ser 441: 117–128, 2011

Arbacia lixula and Paracentrotus lividus are the dominant sea urchins in the Mediterranean sublittoral, where they are... more Arbacia lixula and Paracentrotus lividus are the dominant sea urchins in the Mediterranean sublittoral, where they are key structuring species due to their grazing activity. It has been commonly accepted that competition between both species is minimized by specializing in different algal foods. A. lixula is considered to feed mainly on encrusting coralline algae, while P. lividus prefers fleshy macroalgae. We used stable isotope analysis to test if these species occupy different trophic positions at 3 locations in the western Mediterranean and one in Macaronesia. Our results show unambiguously that A. lixula always occupies a higher trophic level than P. lividus, with a δ15N comparable in some locations to strict carnivores such as Actinia schmidti or Marthasterias glacialis. A temporal monitoring at one locality showed that this signature of a higher trophic level is consistent throughout the year. These results are incompatible with the current belief of an herbivorous diet for A. lixula and suggest that it must be considered an omnivore tending to carnivory in Mediterranean ecosystems, feeding at least partially on sessile animals such as Cirripedia, Hydrozoa or Bryozoa. A parallel analysis of gut contents showed a predominance of vegetal items in both species, although A. lixula consistently had a higher abundance of animal components than P. lividus. Our results challenge the validity of using gut content observations alone for characterizing the trophic behaviour of omnivorous marine invertebrates that feed on a variety of food sources with different digestibility.

Flux by fin: fish-mediated carbon and nutrient flux in the northeastern Gulf of Mexico

by James Nelson

Seagrass meadows are among the most productive
ecosystems in the marine environment. It has been
speculated... more Seagrass meadows are among the most productive
ecosystems in the marine environment. It has been
speculated that much of this production is exported to
adjacent ecosystems via the movements of organisms. Our
study utilized stable isotopes to track seagrass-derived
production into offshore food webs in the northeastern Gulf
of Mexico. We found that gag grouper (Myctereoperca
microlepis) on reefs as far as 90 km from the seagrass beds
incorporate a significant portion of seagrass-derived biomass.
The muscle tissue of gag grouper, a major fisheries
species, was composed on average of 18.5–25% seagrass
habitat-derived biomass. The timing of this annual seagrass
subsidy appears to be important in fueling gag grouper egg
production. The d34S values of gag grouper gonad tissues
varied seasonally and were d34S depleted during the
spawning season indicating that gag utilize the seagrassderived
biomass to support reproduction. If such large scale
trophic subsidies are typical of temperate seagrass systems,
then loss of seagrass production or habitat would result in a
direct loss of offshore fisheries productivity.

Do Non-Native Invasive Fish Support Elevated Lamprey Populations?

by Chris Harrod