The effect of hypoxia and flow decrease in macroinvertebrate functional responses: A trait-based approach to multiple-stressors in mesocosms

• Published in: The Science of the total environment 2018-10, Vol.637-638, p.647-656
• Main Authors: Calapez, A.R., Serra, S.R.Q., Santos, J.M., Branco, P., Ferreira, T., Hein, T., Brito, A.G., Feio, M.J.
• Format: Article
• Language: English
• Subjects: Animals; Aquatic Organisms - physiology; Biodiversity; Biomass; Ecosystem; Ecosystem functions; Environmental Monitoring; Eutrophication; Flow velocity; Hypoxia; Invertebrates - physiology; Mediterranean; Rivers; Streams; Trait diversity
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2018.05.071

River ecosystems are most often subject to multiple co-occurring anthropogenic stressors. Mediterranean streams are particularly affected by water scarcity and organic loads that commonly lead to a simultaneous reduction in flow and increasing depletion of dissolved oxygen. In the present study, the single and combined effects of water scarcity (flow velocity reduction) and dissolved oxygen depletion were used to evaluate alterations of drifting macroinvertebrates on a channel mesocosm system, by employing a multiple trait-based approach. Our main findings confirmed that the impact of the two combined stressors can be implicated in alterations of ecosystem functions as result of the changes in proportions of biological traits. Overall, our results showed that, individually, flow velocity reduction and a severe oxygen depletion promoted a shift in community traits. In more detail, biological traits describing the dispersal of organisms and their respiration showed the strongest responses. The respiration mode responded to low flow with drift increase of gill breathers and decrease of individuals with tegument, whereas dispersal was clearly affected by the combination of stressors. Resistance through eggs was higher with the single effect of flow reduction, while swimmers´ relative abundance increased in individuals that drift after exposure to the combination of stressors. Thus, while flow reduction alone is expected to specifically filter out the gill breathers and the egg producers, the combination of stressors will impact more drastically organism's dispersal and swimmers. Such changes in biological traits can result in variations in ecosystem functioning through, for example, local changes in biomass, secondary production, stream metabolism as well as resulting in biodiversity losses or alterations of its distribution patterns. [Display omitted] •Mediterranean streams are often affected by flow reduction and hypoxia conditions.•Stressors effects on macroinvertebrates functional responses were assessed in a mesocosm system.•Biological traits responded strongly to the effect of single stressors.•Trait alterations may promote ecosystem changes by decreasing functional diversity.