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Monday, March 18, 2019 (10:00 am, Paris Time Zone)
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Ferran ROMERO (ICRA, Girona, Catalonia, Spain)
The effects of global change on river biofilms: a mesocosms approach to elucidate biodiversity-ecosystem function responses to multiple stressors.
Ferran Romero 1, Vicenç Acuña 1, Anna Freixa 1, Sergi Sabater 1,2
- Catalan Institute for Water Research (ICRA)
- Institute of Aquatic Ecology (IEA, University of Girona)
Global change exposes species and ecosystems worldwide to a myriad of stressors differing in their energy, frequency and temporal scale. Particularly, freshwater systems are subject to climate and land-use changes, leading to rivers and streams being exposed to physical, chemical and biological stressors. While most of the times stressor combinations result in additive effects, non-additive interactions might also take place, hindering our prediction capacity. Understanding these multiple stressor effects is still seen today as one of the most pressing challenges in ecology, especially when non-additive interactions like synergism and antagonism occur.
We conducted a manipulative experiment using 24 artificial streams to examine the individual and combined effects of warming (2° C increase in water temperature), hydrological stress (simulated non-flow situation) and chemical stress caused by pesticide exposure (370 ng L-1) on river biofilms. We exposed epilithic and epipsammic biofilms to a replicated full factorial combination of the stressors, including all possible interactions, during 30 days. At the end of the experiment, structural and functional biofilm responses were assessed, including photosynthetic activity, metabolic rates, enzymatic activities, etc.
Hydrological stress showed the strongest negative impacts on river biofilms; these effects were particularly intense for changes in community structure in epilithic biofilm. Accordingly, between 60 % and 70 % of bacterial taxa in this biofilm significantly changed their abundance in response to hydrological stress. This change in community structure translated, at the functional level, into altered photosynthetic capacity and organic matter use, with also potential implications in xenobiotics degradation. Conversely, increased water temperature and pesticide exposure showed less intense effects; between 10 % and 30 % of bacterial taxa in the epipsammic biofilm showed altered abundance as response to warming. Most combinations resulted in non-significant interaction terms, suggesting the prevalence of additive effects. However, non-additive antagonistic interactions also appeared related to increased temperature and pesticides, and affected mainly the community composition of epipsammic biofilms. In addition, interactive effects also translated into antagonistic alterations of ecosystem functions such as changes in the gross primary production and community respiration.
Our study reveals that freshwater biofilms exposed to global change may adapt to physical (i.e. warming and hydrological stress) and chemical stressors by selecting co-tolerant taxa, therefore promoting antagonistic interactions that deviate from a priori predictions and result into altered biodiversity-ecosystem function responses.