Global climate change and other anthropogenic pressures have major impacts on the structure, biodiversity and functioning in aquatic ecosystems. Climate change pressures include transitional environmental change, increased variability and extreme events and long-term disturbance. It is still unclear how these pressures affect ecosystem responses, including their resilience and recovery. Large-scale mesocosm or enclosure experiments provide realistic settings by including higher system complexity in terms of species interactions at various trophic levels. Thus, mesocosm experiments are a powerful tool to obtain a mechanistic understanding of how various global change and other anthropogenic pressures affect ecosystem responses. Moreover, mesocosms offer the unique ability to test possible measures to mitigate or counteract anthropogenic pressures through environmental engineering and nature-based solutions. We welcome presentations on empirical studies where scientific questions about various aspects of aquatic ecosystem functioning have been tested using mesocosms or similar ecosystem level experimentations. We particularly invite scientists that study effects of increasing variability and extreme events on resilience and recovery of biodiversity and ecosystem structure and functioning or regime shifts that change ecosystem structure and functions in response to global climate and environmental change. We strongly encourage early career scientists who have participated in the AQUACOSM or AQUACOSM-plus (www.aquacosm.eu) Transnational Access (TA) programs to present their results from the mesocosm experiments. This session also aims to serve as a meeting point for all persons interested in ecosystems scale experimentation on a global scale (see mesocosm.org).
Lead Organizer: Stella Berger, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) (stella.berger@igb-berlin.de)
Co-organizers:
Jens Nejstgaard, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB) (jens.nejstgaard@igb-berlin.de)
Tatiana M Tsagaraki, University of Bergen, Department of Biological Sciences (tatiana.tsagaraki@uib.no)
Meryem Beklioğlu, Middle East Technical University (meryem@metu.edu.tr)
Behzad Mostajir, Marine Biodiversity, Exploitation and Conservation (MARBEC), University of Montpellier-CNRS-Ifremer-IRD (behzad.mostajir@umontpellier.fr)
Presentations
03:00 PM
BACTERIA IN STRESS: EFFECT OF MULTIPLE STRESSORS ON MICROBIAL DEGRADATION OF ORGANIC CARBON IN RIVER ECOSYSTEM AS REVEALED BY MESOCOSM EXPERIMENTS (5691)
Primary Presenter: Daria Baikova, University of Duisburg-Essen (baikovadaria@gmail.com)
Rivers play a substantial role in the global carbon cycle through their high rates of carbon respiration and sequestration. Dissolved organic carbon (DOC) in such ecosystems is an integral part in biogeochemical cycling. Microorganisms are the key organism group responsible for DOC turnover providing a crucial ecosystem function. However, rivers are impacted in multiple ways by anthropogenic pollution and climate change whereas salinization and temperature rise is a global trend. Hence, the goal of this research is to investigate the effects of salinity and temperature on microbial communities and their ecosystem function to degrade DOC in river water and sediments. The influence of these stressors is studied on an urban river in laboratory microcosms and in outdoor mesocosms. The degradation rates of DOC to CO2 were quantified via a novel Reverse Stable Isotope Labelling method measuring isotope ratios in CO2 with an isotope analyzer. Our results showed that raising the salinity by 250 mgCl/L and temperature by 3 °C significantly increased degradation rates in river sediments from 0.34 to 1.34 mgC/L/d after stress release, while having no significant effect during stress application. In the water column an increase of salinity by 1.5 gCl/L and temperature by 5 °C tripled the degradation rates in the recovery phase where the stress was released. Carbon degradation rates in water were 30 times lower than in sediments presumably due to lower organic matter quantity and the 10-fold lower organism density as revealed by flow cytometric analysis.
03:15 PM
EARLY TRAJECTORIES OF MICROBIAL COMMUNITIES AND ORGANIC MATTER DURING COLONIZATION IN ARTIFICIAL FRESHWATER ECOSYSTEMS (6809)
Primary Presenter: Julie Leloup, Sorbonne Université (jleloup@sorbonne-universite.fr)
The trajectory of microbial colonization within newly formed aquatic ecosystems is still not well documented. In particular, we do not know the importance of trophic status and environmental conditions on this trajectory. One main hypothesis is based on the competitive exclusion of microbial species along an environmental gradient according to their nutritional strategies: “Specialist” species should colonize stable and thus mature ecosystems, while “generalist” ones should appear in “young” ecosystems where a larger pool of resources is available. This would lead to the replacement of “generalist” species, that would be more tolerant to environmental perturbations, by “specialist” ones relative to well defined ecological niches (mostly the organic matter and nutrients). To explore this hypothesis, we realized a 1-year survey of the microbial colonization within the 16 artificial ponds of the PLANAQUA platform (PLAteforme expérimentale Nationale d'écologie AQUAtique, CEREEP-France), during their first impoundment. For eight of them an enrichment in mineral N and P was performed at the beginning of the phytoplankton growth to stimulate a eutrophication phenomenon. We explored whether the microbial communities and the organic matter, in term of quality, quantity, taxonomical and functional richness, were synchronized, and whether simulation of eutrophication modified these trajectories. To do so, we determined the abundance and the taxonomical and functional diversity of the major microbial groups (phytoplankton, bacteria, archaea and virus), in combination with the diversity of dissolved organic matter (cDOM spectral analysis) and classical in situ multi-parameters. Altogether, these data suggest that microbial communities of these new artificial ecosystems rapidly converged toward those of natural freshwater ecosystems. Our results provide new insight into colonization process and community assembly mechanisms, and underlie the role of the microbial loop in the stability of aquatic ecosystems.
03:30 PM
Nutrient enrichment destabilizes meta-ecosystems in linked freshwater mesocosms (7287)
Primary Presenter: Egor Katkov, McGill University (egor.katkov@gmail.com)
Nutrient enrichment has been found to have a destabilizing effect on ecosystems in mathematical models, and laboratory and field experiments. Further modeling efforts have demonstrated that nutrient enrichment in one node of a meta-ecosystem can destabilize consumer-resource dynamics in connected nodes. We tested the destabilizing effect of nutrient enrichment on local and distal dynamics in freshwater aquatic mesocosms at different levels of enrichment and connectivity using single- and two-node networks using a fractional factorial experimental design. We performed weekly unidirectional water transfer from the upstream to the downstream nodes, replenishment of the upstream nodes with freshwater and nutrient addition for 15 weeks. Although we did not find that the usual measure for stability, the coefficient of variation of chlorophyll <i>a</i>, was affected by nutrient enrichment or connectivity, we found that average chlorophyll <i>a</i> increased in response to nutrient enrichment, whereas the effects of connectivity was exclusively time-dependent. Furthermore, we found that as connectivity between paired nodes increased, the cross-correlation of chlorophyll <i>a</i> over time between paired nodes also increased. Additionally, we found negative effects of nutrient enrichment on zooplankton diversity. Overall, our results support the model predictions that with sufficient levels of connectivity, the destabilization of an upstream node in a semi-natural meta-ecosystem can destabilize downstream nodes.
03:45 PM
Effects of temperature and terrestrial organic matter inputs on freshwater microbial communities in a mesocosm experiment (5694)
Primary Presenter: Dominique Lamy, Sorbonne University (dominique.lamy@sorbonne-universite.fr)
Organic matter of terrigenous origin (t-OM) can represent a substantial contribution of allochthonous carbon to freshwater ecosystems. These inputs have intensified over the last few decades, in particular as a result of climate change. The intensification of t-OM fluxes combined with warming could deeply impact microbial heterotrophic activities in aquatic environments, and thus alter the capacity of these ecosystems to be sources or sinks of carbon. The amplitude and the persistence over time of such impacts, as well as the nature of the heterotrophic activities impacted, remain however poorly explored. Warming and t-OM enrichment were cross-simulated in 1000L-mesocosms filled with lake water, with a total of four conditions in triplicates: control (in situ natural water temperature), +t-OM, +6°C, both +t-OM and +6°C. The utilization pattern of different carbon substrates (© Biolog Ecoplates), coupled with bacterial abundance (flow cytometry), community respiration (O2 optodes) and aminopeptidase exo-enzymatic activity (fluorogenic substrate analog) were measured over a 40-days experiment. The optical properties of the colored DOM (cDOM) was also followed over time and showed a clear t-OM signature on the initial OM pool until the end of the experiment. Warming, alone or combined with t-OM inputs, enhanced microbial activities (by a mean factor of 1.6 and 2.2 for aminopeptidase activity and community respiration, respectively), while bacterial abundances increased also in the +t-OM treatment. Bacteria used more carboxylic acids and polymers under higher temperature, with or without t-OM, while the t-OM inputs slightly enhanced the use of amines. We highlighted that t-OM inputs combined with warming not only impact the rate of organic matter utilization but also the diversity of substrates utilized, reflecting the degradation of the complex molecules composing the tDOM.
04:00 PM
Combined effects of warming and pharmaceuticals on freshwater food webs: a mesocosm study (7180)
Primary Presenter: David Boukal, University of South Bohemia in Ceske Budejovice (dboukal@prf.jcu.cz)
Global warming and chemical pollution are two ubiquitous stressors that cause rapid environmental change and pose a major threat to biodiversity and ecosystem functioning. We investigated the combined effects of +4°C warming and a mixture of commonly used pharmaceutically active compounds (PhACs) on a pelagic invertebrate community in outdoor mesocosms that mimic small freshwater ponds (1 m3 volume). The experiment was conducted twice (in winter and summer). The effects of warming and PhACs differed greatly between seasons and trophic levels. The PhAC mixture reduced phytoplankton biomass and altered odonate larval development in summer, while it had only marginal effects on the community in winter. Warming reduced the survival of predatory aquatic insects in winter and accelerated their development in summer, partially releasing large zooplankton from top-down control. Finally, phytoplankton biomass increased with warming in the summer, but not in the winter experiment. Our results show that the effects of combined stressors on freshwater communities are context-dependent and that warming can either mask or amplify the effects of anthropogenic pollutants on freshwater communities.
04:15 PM
Plankton community response to climate-driven salinity change and warming: A mesocosm experiment comparing morphology‐based identification and metabarcoding. (6268)
Primary Presenter: Clio Hall, University of Helsinki (clio.hall@helsinki.fi)
Current climate change predictions indicate global changes in salinity and temperature, with negative implications for the plankton food web, which plays a crucial role in the functioning of marine ecosystems. Current understanding of how salinity change will impact plankton communities has focused mainly on the salinisation of freshwater environments, with little known about changes in marine systems as well as potential synergistic effects with other stressors, such as warming. We investigate the effect of salinity change coupled with warming on plankton community composition under different climate change scenarios of the Baltic Sea. Projections for future salinity change and warming were used to set-up an indoor mesocosm experiment in the Gulf of Finland. We identified plankton communities combining traditional morphology and environmental DNA (eDNA) metabarcoding of the mitochondrial cytochrome oxidase I (COI) and 18S rRNA genes. Our results suggest shifts in plankton community composition is dependent on both salinity and temperature treatments. Additionally, changes in plankton community assemblage in the different mesocosm treatments were more clearly captured by metabarcoding than by morphology-based methods. Our results asses the sensitivity of planktonic community assemblages to variations in seawater salinity and temperature in the Baltic Sea across all trophic levels of the food web. We also highlight the potential of eDNA metabarcoding to monitor plankton community responses to climate change.
SS046C Mesocosm Based Experimental Studies to Address Challenges Emerging From Global Change on Stability of Aquatic Ecosystems
Description
Time: 3:00 PM
Date: 5/6/2023
Room: Auditorium Illes Balears