Mesocosms and other ecosystem-scale experimental approaches are among the very strongest tools to “take the pulse and assess the state of our aquatic systems, whether that is through reconstructing the past, observing the current state, or predicting the future of our lakes, rivers, estuaries, and oceans.” Mesocosms are not only powerful tools to obtain a mechanistic quantitative understanding of how various global change and other perturbations drive ecosystem responses, they also 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 studies where scientific questions about various aspects of aquatic ecosystem functioning have been tested through using mesocosms or similar ecosystem level experimentations. We particularly invite scientists that study effects of increasing variability and extreme events on ecosystem responses including resistance, resilience, recovery of ecosystem structures, biodiversity or regime shifts that change ecosystem functions in response to global climate and environmental change. We strongly encourage early career participants to present results. We also encourage to present plans for future activities open to external participation, as this session also aims to serve as a meeting point for all persons interested in ecosystems scale experimentation on a global scale (see e.g. https://mesocosm.org). We indeed aim to host a session that will “reflect on how our decisions today will manifest in the environment tomorrow” by promoting a lively session fostering new collaborations across areas and disciplines, extending the success of the 3-day mesocosm session at ASLO-ASM 2023 Mallorca meeting.
Lead Organizer: Jens C Nejstgaard, IGB - Leibniz-Institute of Freshwater Ecology and Inland Fisheries (jens.nejstgaard@igb-berlin.de)
Co-organizers:
Stella A Berger, IGB - Leibniz-Institute of Freshwater Ecology and Inland Fisheries (stella.berger@igb-berlin.de)
Paraskevi Pitta, HCMR - Hellenic Centre for Marine Research (vpitta@hcmr.gr)
Meryem Beklioğlu, METU - Middle East Technical University (meryem@metu.edu.tr)
Behzad Mostajir, MARBEC - Marine Biodiversity, Exploitation and Conservation, University of Montpellier-CNRS-Ifremer-IRD (behzad.mostajir@umontpellier.fr)
Presentations
02:30 PM
Impact of salinization on ecosystem structure, function and diversity in shallow lakes using a gradient design synchronized mesocosm experiments (9433)
Primary Presenter: Meryem Beklioglu, Middle East Technical University (meryem@metu.edu.tr)
The widespread salinization of freshwater ecosystems is among the major grand challenges that poses a major threat to ecosystem structure, function and biodiversity that .is especially common in arid and semi arid areas coupled with excessive water use for irrigation of water-thirsty crops e.g. Central Anatolian Türkiye. To understand the effects of salinization on shallow lakes, we performed synchronized long-term gradient design mesocosm experiments between September 2021 to May 2022 with 16 different salinities (0-50 g/L), in two places with different climate conditions in Türkiye (Ankara, mean temperature: 12.6°C; and Mersin, mean temperature: 20.1°C). The experiments were divided into three periods: increasing (30 days), stable (six months), and decreasing (40 days) salinity. In both places, the concentrations of nutrients, especially phosphorus, chlorophyll-a, turbidity and suspended solids increased, which was more pronounced after 20 g/l of salinity. Overall, the increase was much higher in the warmer Mersin mesocosms. Increasing salinity led to a linear decrease in water clarity in Ankara while it did not cause a change in Mersin mesocosms during the increasing salinity period. At stable levels, intermediate salinities showed higher water transparency in both places. Increased salinity shifted phytoplankton community structure to more Cyanobacteria and diatoms dominated. Zooplankton biomass and richness decreased largely with increasing salinity. Changes took place along the salinity gradient in two different climatic zones will be discussed in depth
02:45 PM
Assessing the effects of freshwater salinization and heatwaves on zooplankton community biomass and size structure. (9155)
Primary Presenter: Hannah Cane, Rubenstein Ecosystem Science Laboratory, University of Vermont (hcane@uvm.edu)
Awareness of the impact of multiple stressors on freshwater ecosystems is increasing. For example, heatwaves are increasingly common due to climate change, and chloride (Cl-) concentrations are rising in inland waters due to human activities. Both stressors threaten freshwater wildlife, biodiversity, and ecosystem services, individually and in tandem. Zooplankton are primary consumers that play important roles in ecosystems, such as regulating algal growth and nutrient cycling. The mechanisms by which heatwaves and Cl- affect zooplankton biomass, composition, and body size are not well known. We evaluated how fluctuations in zooplankton biomass could be attributed to (H1) abundance declines, (H2) compositional shifts in community size structure, or (H3) intraspecific size responses. We also tested for synergistic interactive effects when elevated temperatures and salinity co-occurred (H4). We performed a 6-week experimental study using nine indoor mesocosms to assess plankton responses to heatwaves and elevated Cl- conditions with a pulse treatment design. Preliminary results indicate that zooplankton biomass generally remained unaffected by treatments. However, zooplankton community-weighted mean body size decreased in response to elevated Cl-, alone or combined with heatwaves. Heatwaves alone only affected zooplankton body size after the first pulse, suggesting increased community resistance upon subsequent pulses. Overall, this work will provide insight into the mechanisms that drive zooplankton community responses to co-occurring stressors in freshwater ecosystems.
03:00 PM
EFFECTS OF A MARINE HEATWAVE ON COASTAL ATLANTIC PLANKTON COMMUNITIES IN THE RÍA DE VIGO, NW SPAIN: A MESOCOSM EXPERIMENT WITH AUTOMATED SENSOR MEASUREMENTS (8865)
Primary Presenter: Tanguy Soulié, University of Montpellier-CNRS (tanguy.soulie@gmail.com)
Marine heatwaves (HW), predicted to increase in frequency and intensity due to climate change, can significantly impact marine ecosystems, and notably plankton communities. A mesocosm experiment was performed to investigate the effects of a simulated HW on the metabolism and functioning of coastal plankton communities in the Ría de Vigo (NW Spain) during post-upwelling conditions (April-May 2023). Water temperature was raised by +3°C in triplicate HW mesocosms, compared to triplicate control mesocosms which followed natural temperature variations of the Ría. High-frequency (every minute) monitoring from automated sensors was used to estimate Gross Primary Production (GPP), community Respiration (R), phytoplankton growth (µ), and loss (L) rates. Daily manual sampling of the mesocosms enabled to monitor nutrient concentrations, phytoplankton community composition, size structure, and photosynthetic efficiency. The HW increased both GPP and R by 79% and 90%, respectively, without altering the metabolic index (GPP:R ratio). Phytoplankton µ was enhanced under HW conditions at the beginning of the experiment, shifting the trophic index (µ:L ratio) of the community toward biomass accumulation, while L increased during the second half. The HW enhanced photosynthetic efficiency, and shifted community and size structure, favoring prymnesiophytes over diatoms and dinoflagellates, key players in the Ría's ecosystem. Overall, the HW enhanced metabolic and trophic indexes, suggesting that Atlantic coastal upwelling systems may become biogeochemical hotspots under future HW conditions.
03:15 PM
Using mesocosms and long-term data to explore the impacts of zebra mussels on the microbial food web of a eutrophic lake (8964)
Primary Presenter: Tyler Butts, University of Wisconsin-Madison (tyler.james.butts@gmail.com)
Invasive species pose a global challenge for aquatic ecosystem function and resilience. Understanding how they alter long-term food web structure and ecosystem function is crucial for effectively managing aquatic ecosystems in our current era of global change. Forecasting the impacts of invasive species is notoriously difficult, especially at lower trophic levels where impacts can cascade up and down trophic levels. Lake Mendota, WI experienced two successive invasions over the past 25 years: spiny water flea (2009; Bythotrephes longimanus) and zebra mussels (2015; Dreissena polymorpha). Despite the well-known impacts of zebra mussels on aquatic ecosystems, their impacts on the entire lower food web—zooplankton, phytoplankton, protists, and microbes—are less understood, particularly within cyanobacteria-dominated eutrophic lakes. We designed a mesocosm experiment to quantify zebra mussel impacts on phytoplankton, protists, and microbes in Lake Mendota and compared our results to a 20-year record of zooplankton, phytoplankton, protist and microbial dynamics. We show how zebra mussels have lower ecological impact under cyanobacteria-dominant conditions and compare the effects within zooplankton-dominated and protist-dominated mesocosms. We then place our mesocosm findings within the context of long-term trends and successive species invasions within the lower food web of Lake Mendota. Understanding these complex interactions is crucial for taking the pulse of our aquatic ecosystems and developing effective management paradigms for the future.
03:30 PM
Identifying the effects of offshore wind farm noise on the plankton food web (9022)
Primary Presenter: Justine Courboulès, Norwegian University of Science and Technology (NTNU) (justine.courboules@hotmail.fr)
Offshore Wind Farms (OWF) offer a low-CO2 emission alternative to fossil fuels. However, they can still be the source of anthropogenic pollution by generating noise that impacts marine life. Noise emitted by OWF is characterized by low frequencies at a high enough noise level that can affect marine mammals and fishes. To date there is a large knowledge gap concerning the effects of OWF noise on plankton communities. To better understand how plankton responds when they are exposed to OWF noise, an in situ mesocosm experiment was performed in summer 2024 in the Bay of Hopavågen, in Norway. During this experiment a recording from an OWF was broadcasted underwater for 18 days. Three mesocosms were placed in situ next to the speaker and received an average noise level of 97 dB re: 1 μPa over 100-2000 Hz, while three control mesocosms were placed further away in a part of the bay acoustically isolated from the noise treatment, where they only experienced ambient noise of 70-80 dB. During the experiment, plankton communities and abiotic variables were closely monitored. Specifically, virus, bacteria, phytoplankton, proto- and metazooplankton communities as well as nutrients were sampled every second day. Concurrently, temperature, salinity, light, dissolved oxygen and chlorophyll-a concentrations were monitored in each mesocosm using automated sensors. The abiotic variables were identical between the control and noise treatments, however differences in phytoplankton pigment concentrations and zooplankton abundance indicated that the OWF noise affected the plankton food web.
03:45 PM
RESOURCE DISTRIBUTION AND CONSUMER MOBILITY DETERMINE MACROZOOBENTHOS – MICROALGAE INTERACTIONS IN TIDAL FLATS (9198)
Primary Presenter: Stefanie Moorthi, Carl-von-Ossietzky Universität Oldenburg (moorthi@icbm.de)
Benthic microalgae (microphytobenthos, MPB) are important primary producers in shallow coastal marine sediments and comprise a high taxonomic and functional diversity regarding mobility, resource acquisition and grazing tolerance. MPB distribution, biomass and composition thus reflect variable patterns of nutrients, light availability, grazing and hydrodynamically forced dispersal. Despite high MPB functional diversity and patchy distribution, spatially coupled consumer-resource interactions have rarely been explored in this system so far. Conducting a benthic mesocosm experiment, the current study investigated the interactive effects of spatial nutrient distribution and grazing by macrozoobenthic consumers of differing mobility on the biomass, diversity and composition of a multispecies MPB community. Before grazer addition, nutrient supply mode didn’t affect MPB biomass, but altered MPB diversity and composition, leading to increased MPB diversity under heterogeneous nutrient supply. Grazing effects depended on consumer mobility and nutrient distribution. Mobile consumers exerted a significantly higher grazing pressure on MPB biomass compared to sedentary consumers, and this effect was stronger under homogenous nutrient supply. MPB diversity was significantly higher with mobile consumers and under homogenous nutrient supply. This study enhances our comprehensive understanding of resource-driven consumer-microalgae interactions in tidal flat communities and emphasizes the relevance of incorporating a spatial context when studying this highly variable ecosystem.
SS40A - Understanding, forecasting and mitigating global challenges for aquatic ecosystem functioning and resilience using mesocosms and other ecosystem-scale experimental approaches
Description
Time: 2:30 PM
Date: 30/3/2025
Room: W206A