-We used flume experiments to study the effects of a temporary increase in stream flow on macroinvertebrates, leaf litter breakdown and soft-bodied benthic algae; both as a single stressor and eventually in combination with an increase in nutrient supply. In order to understand how well the flumes reflected the nearby stream ecosystem, we compared species composition of macroinvertebrates and benthic algae between the flumes and the nearby stream from which the flumes were supplied with water. As single stressors, nutrient addition and an increased flow velocity from 1.3 to 2.8 cm s À 1 lead to an increase in the biomass of benthic algae, likely reflecting an improved transfer of nutrients into algal patches. However, the combined effect of flow and nutrient addition was smaller than the sum of both individual effects, likely because an increased biomass also was more susceptible to scouring. We found differences in macroinvertebrate and benthic algal taxon identity and abundance between stream and flumes. Since biodiversity is assumed to stabilize ecological functioning in response to disturbances and variation, we conclude that care should be taken in applying results from small scale experiments to stream ecosystems. Nous avons utilisé des expériences en canaux pour étudier les effets d'une augmentation temporaire du débit sur les macroinvertébrés, la dégradation de la litière foliaire et les algues benthiques à corps mou, à la fois comme stresseur unique et éventuellement en combinaison avec une augmentation de l'apport en éléments nutritifs. Afin de comprendre dans quelle mesure les canaux reflétaient bien l'écosystème du cours d'eau voisin, nous avons comparé la composition spécifique des macroinvertébrés et des algues benthiques entre les canaux et le cours d'eau voisin qui alimentait les canaux en eau. En tant que stresseurs uniques, l'ajout de nutriments et une vitesse d'écoulement accrue de 1,3 à 2,8 cm s À 1 entraînent une augmentation de la biomasse des algues benthiques, ce qui reflète probablement un meilleur transfert des nutriments dans le périphyton algal. Toutefois, l'effet combiné du débit et de l'adjonction de nutriments était plus faible que la somme des deux effets individuels, probablement parce qu'une biomasse accrue était aussi plus susceptible de se décoller. Nous avons trouvé des différences dans l'identité et l'abondance des taxons de macroinvertébrés et des taxons d'algues benthiques entre le cours d'eau et les canaux. Puisque la biodiversité est supposée stabiliser le fonctionnement écologique en réponse aux perturbations et aux variations, nous concluons qu'il faut faire preuve de prudence dans l'application aux écosystèmes des cours d'eau des résultats d'expériences à petite échelle.
Use of fast-growing domesticated and/or genetically modified strains of fish is becoming increasingly common in aquaculture, increasing the likelihood of deliberate or accidental introductions into the wild. To date, their ecological impacts on ecosystems remain to be quantified. Here, using a controlled phenotype manipulation by implanting growth hormone in juvenile Atlantic salmon (Salmo salar), we found that growth-enhanced fish display changes in several phenotypic traits known to be important for ecosystem functioning, such as habitat use, morphology and excretion rate. Furthermore, these phenotypic changes were associated with significant impacts on the invertebrate community and key stream ecosystem functions such as primary production and leaf-litter decomposition. These findings provide novel evidence that introductions of growth-enhanced fish into the wild can affect the functioning of natural ecosystems and represent a form of intraspecific invasion.Consequently, environmental impact assessments of growth-enhanced organisms need to explicitly consider ecosystem-level effects.
Biodiversity assessments using molecular identification of organisms through high-throughput sequencing techniques have been a game changer in ecosystem monitoring, providing increased taxonomic resolution, more objective identifications, potential cost reductions, and reduced processing times. The use of DNA metabarcoding of bulk samples and environmental DNA (eDNA) is now widespread but is not yet universally implemented in national monitoring programs. While bulk sample metabarcoding involves extraction of DNA from organisms in a sample, eDNA analysis involves obtaining DNA directly from environmental samples, which can include microorganisms, meiofauna-size taxa and macrofauna traces such as larval stages, skin and hair cells, gametes, faeces and free DNA bound to particles. In Norway, freshwater biomonitoring in compliance with the EU Water Framework Directive (WFD) is conducted on several administrative levels, including national monitoring programs for running water, small and large lakes. These programs typically focus on a fraction of the actual biodiversity present in the monitored habitats (Weigand 2019). DNA metabarcoding of both bulk samples and eDNA samples are relevant tools for future freshwater biomonitoring in Norway. The aim of this PhD project is to develop assessment protocols based on DNA-metabarcoding and eDNA of benthic invertebrates, microcrustaceans and fish that can be used as standard biomonitoring tools to assess the ecological condition of lakes. The main topics addressed will be: - Development of protocols throughout the eDNA-metabarcoding workflow (i.e. sampling, filtration, preservation, extraction, amplification and sequencing) suitable to execute biodiversity assessments and determine the ecological status of lakes. - Comparison of the results obtained using molecular tools and traditional morphology-based approaches in order to assess the feasibility of such techniques to be incorporated as standard biomonitoring tools, such as the ones implemented under the provisions of the WFD. - Evaluate the effect of improved taxonomic resolution from molecular techniques on determining the ecological status of lakes, both by broadening the number of taxa analyzed and by identifying more taxa to species level. - Assess the feasibility of using eDNA extracted from water samples, taken at different depths and fish densities, to measure fish abundance/biomass as a proxy to calculate the ecological quality indices regulated in the WFD. - Analyze the coverage and resolution provided by reference libraries for certain taxa, such as crustacea, in order to assess the reliability and precision of taxonomic assignments.
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