title: Can salinity trigger cascade effects on streams? A mesocosm approach.
abstract: Human activities have greatly increased the salt concentration of the world's rivers, and this might be amplified by water scarcity in the future. While the lethal effects of salinity have been documented for a wide variety of stream invertebrates, the sub-lethal effects (i.e. changes in biological condition without mortality) are not deeply understood yet. One important sub-lethal effect that has yet to be investigated is changes in predation efficiency, which could trigger cascade effects associated to the abundance of herbivorous invertebrates that control algae biomass. In this study we combined the use of biomarkers with community-level data in a stream mesocosm to evaluate the potential cascade effect of increased salinity on the trophic food web. Both predation and salt treatments had an effect on the aquatic invertebrate abundance, richness and community composition. The presence of predators had a clear cascade effect, it reduced herbivorous invertebrate abundance and richness leading to higher chlorophyll a concentrations. The salt treatment significantly reduced taxa richness, but only in the gravel bed. The predators were significantly stressed by salt addition, as shown by the different analyzed biomarkers. Concordantly, in the presence of predators, Tanytarsini registered higher abundances and chlorophyll a showed a lower concentration when salt was added. However, none of these changes was significant. Therefore, although salt addition significantly stressed Dina lineata, our results suggest that a longer exposure time is needed to fully capture cascading effects (e.g. a decrease in chlorophyll a due to a relaxation of predation on herbivorous invertebrates). We suggest that the potential cascade effects of salinization need to be evaluated when addressing the impacts of water scarcity (as caused by climate change and increasing water demand) on river ecosystems, since flow reductions will lead to higher salt concentrations.
authors.affiliation: BETA Technology Centre, Aquatic Ecology Group, University of Vic - Central University of Catalonia, Spain; Freshwater Ecology and Management (F.E.M.) Research Group, Departament d'Ecologia, Universitat Barcelona, Diagonal, 643, 08028 Barcelona, Catalonia, Spain.
authors.forename: Miguel
authors.initials: M
authors.lastname: Cañedo-Argüelles
authors.affiliation: Freshwater Ecology and Management (F.E.M.) Research Group, Departament d'Ecologia, Universitat Barcelona, Diagonal, 643, 08028 Barcelona, Catalonia, Spain.
authors.forename: Miquel
authors.initials: M
authors.lastname: Sala
authors.affiliation: Freshwater Ecology and Management (F.E.M.) Research Group, Departament d'Ecologia, Universitat Barcelona, Diagonal, 643, 08028 Barcelona, Catalonia, Spain.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Peixoto
authors.affiliation: Freshwater Ecology and Management (F.E.M.) Research Group, Departament d'Ecologia, Universitat Barcelona, Diagonal, 643, 08028 Barcelona, Catalonia, Spain.
authors.forename: Narcís
authors.initials: N
authors.lastname: Prat
authors.affiliation: CESAM & Departamento de Biologia, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Melissa
authors.initials: M
authors.lastname: Faria
authors.affiliation: CESAM & Departamento de Biologia, Universidade de Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Amadeu M V M
authors.initials: AM
authors.lastname: Soares
authors.affiliation: Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Barata
authors.affiliation: Institute for Applied Ecology, University of Canberra, ACT 2601, Australia.
authors.forename: Ben
authors.initials: B
authors.lastname: Kefford
mesh_terms: D000818:Animals; D002734:Chlorophyll; D000077194:Chlorophyll A; D017753:Ecosystem; D004784:Environmental Monitoring; D020387:Food Chain; D007448:Invertebrates / Q000502:physiology*; D045483:Rivers / Q000737:chemistry*; D054712:Salinity; D014876:Water Pollution
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: Aquatic invertebrates; Artificial streams; Biomarkers; Cascade effects; Predation; Salinization; Sub-lethal effects; Toxicity