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
08:30 AM
PELAGIC FOOD-WEB STRUCTURE, TROPHIC INTERACTIONS AND ROLE OF ZOOPLANKTON FOR TROPHIC TRANSFER EFFICIENCY IN THE HUMBOLDT CURRENT UPWELLING SYSTEM OFF PERU (6800)
Primary Presenter: Jens Nejstgaard, IGB Leibniz-Institute of Freshwater Ecology and Inland Fisheries (jens.nejstgaard@igb-berlin.de)
While the fishery on the Peruvian anchovy in the northern Humboldt Current upwelling system off Peru (HUS) is the world’s largest single-species fishery, the primary production is not the largest leading to a paradoxical 5–10 times higher fishery yield in the HUS compared to other eastern boundary upwelling systems. It is not fully understood how the food web can sustain this exceptional trophic transfer efficiency and how it relates to upwelling and light intensities. The relationship between upwelling intensity and productivity is also not sufficiently understood to predict the effect of climate change on the ecosystem. A mismatch between upwelling intensity and phytoplankton productivity proposed by Messié and Chavez (2015) suggests that while upwelling is highest in winter, primary productivity peaks in summer. To test the hypothesis that light causes the out-of-phase observations, and to improve our understanding of trophic processes controlling productivity in the HUS, we simulated winter low light and summer high light conditions during a 35-day mesocosm experiment 6 km off-shore from Callao/Lima during austral summer 2020. Natural plankton was enclosed in 9 mesocosms (KOSMOS, GEOMAR Kiel) and five levels of upwelling intensities were simulated by adding nutrient-rich deep water (0%, 15%, 30%, 45% and 60%). We present the first comprehensive data from this experiment, on the pelagic food-web structure, trophic interactions and role of the micro- and mesozooplankton in overall trophic transfer efficiency to fish.
08:45 AM
RURAL AND URBAN ATMOSPHERIC PARTICLES VS SAHARAN DUST: IMPACT ON THE PLANKTONIC, MICROBIAL FOOD WEB OF THE ULTRA-OLIGOTROPHIC EASTERN MEDITERRANEAN SEA (5704)
Primary Presenter: Vivi Pitta, Hellenic Centre for Marine Research (vpitta@hcmr.gr)
Large amounts of Saharan dust and atmospheric particles are annually deposited at the surface Eastern Mediterranean Sea, providing macro-nutrients, micro-trace metals and microbes to this ultra-oligotrophic area and therefore affecting this ecosystem’s function and diversity. The impact of bioaerosols, emitted from rural and urban areas but also those from Saharan dust, on the plankton community structure was examined during a mesocosm experiment using water from the Cretan Sea in May-June 2022. Multiple additions of bioaerosols took place in 6 mesocosms, followed by two additions of Saharan dust collected during an intense deposition event; three more mesocosms served as a control during the 10 days-experiment. Changes induced from these additions, on the autotrophic and heterotrophic surface microbial populations, were studied from viruses to zooplankton. The results suggested that not all autotrophic groups were favored by the available nutrients, introduced via aerosols/dust additions, but only autotrophic flagellates and diatoms. Dinoflagellates and zooplankton were indirectly favored as they preyed on the groups that took advantage of the available nutrients. Saharan dust was found to be a greater trigger of specific plankton and microbial populations compared to bioaerosols. The results of this study are compared to two previous mesocosm experiments (with addition of Saharan dust and mixed-urban aerosols) conducted at the same area.
09:00 AM
Impact of Water Loss and Salinization on Shallow Lakes of Arid Landscapes: A Field Survey and a Mesocosm Experiment in Two Different Climate Zones in Türkiye (6686)
Primary Presenter: Korhan Ozkan, Middle East Technical University (korhan.ozkan@gmail.com)
Shallow lakes located in dry landscapes face dramatic ecosystem changes caused by water loss and salinisation due to excessive water use and climate change. To understand the effects of these pressures on the ecology of lakes, we conducted a field survey across Anatolia and a synchronised mesocosm experiment in two climate zones in Türkiye. The field survey conducted over more than 40 lakes revealed a dramatic loss of biodiversity driven by salinisation and water loss, besides significant changes in lake ecosystem function across a large salinity gradient. We conducted two parallel long-term mesocosm experiments (September-2021 to May-2022), with 16 different salinities (0-50 g/L), in central and coastal Türkiye with different climatic conditions (temperate vs. subtropical). The salinity treatments were applied in three periods: increasing (30 days), stable (six months), and decreasing (40 days) salinities. Salinisation resulted in higher phosphorus and chlorophyll-a concentrations in the mesocosms, being more pronounced at salinities >20 g/L. Furthermore, salinisation significantly modified oxygen concentrations and turbidity contrastingly in different climate zones. Significant shifts in the community composition of plankton were observed over the salinity gradient with a loss of diversity. Overall, salinisation significantly impacted water quality, being also affected by climate. Both field surveys and mesocosm experiments revealed a predominant negative effects of water loss and salinisation on biodiversity, ecosystem metabolism, and, thus, on the ecosystem functioning of lakes.
09:15 AM
FROM MESOCOSMS TO ECOSYSTEMS: USING DISSOLVED N2:AR RATIOS TO DETECT HOT SPOTS AND HOT MOMENTS OF LAKE N2 FLUX IN A CHANGING WORLD (6130)
Primary Presenter: Jason Taylor, USDA-ARS NSL (jason.taylor@usda.gov)
Humans are fundamentally changing the nitrogen (N) cycle. Simple measures to detect aquatic N2 fluxes are needed. We measured dissolved N2:Ar patterns in twelve experimental pond mesocosms representing a N:P input gradient ranging from ~2 to 110 (molar). Low N:P mesocosms had N2:Ar saturation ratio values consistently below equilibrium (net N fixation), and high N:P mesocosms had N2:Ar values above equilibrium (net denitrification). Both planktonic N fixation estimated from isotope mixing models and N2 fluxes measured by sediment core incubations confirmed a shift from net N fixation to net denitrification as N:P ratios increased. Photic zone N2:Ar saturation ratios were negatively correlated with increasing measured N fixation while saturation ratios from benthic waters were positively correlated with increasing sediment N2-N flux. Field measurements of N2:Ar ratios in excess of equilibrium in the hypolimnion of 8 off-channel lakes of the Lower Mississippi River (LMR) confirmed that these backwater habitats are significant denitrification habitatsduring summer disconnection from the river. However, we also observed evidence for net N fixation with depleted N2:Ar ratios in the epilimnion of all lakes. Our mesocosm results combined with our field study demonstrate that N2:Ar ratios can be used to identify hotspots or hot moments of net denitrification and N fixation. Delineating the direction and magnitude of N2 flux in space and time at larger scales may improve understanding of global changes in aquatic N cycling.
09:30 AM
Dissolved oxygen and dinitrogen gas dynamics in experimental lake mesocosms experiencing forced stratification (6877)
Primary Presenter: Mark McCarthy, Estonian University of Life Sciences (mark.mccarthy@emu.ee)
The Lake Mesocosm Warming Experiment (LMWE) in Silkeborg, Denmark, has been running since 2003, with the goal of studying climate warming and nutrient pollution effects on lake ecosystems. Water levels in the 24 mesocosms (1.9 m diameter, 1 m water depth, 0.2 m sediment depth) are maintained with groundwater, continuously mixed using mechanical paddles, and heated to treatment temperatures with submerged heating elements. Mesocosm temperatures are either ambient, ambient plus ~2 deg C, or ambient plus ~4 deg C, and mesocosms within each temperature group are further treated with low (groundwater only) or high nutrients (added NO3-N and PO4-P). During summer 2021, mixing paddles were turned off/on for 2-week periods. We collected water samples above and below thermoclines during no mixing, and depth-integrated water samples during mixing, for initial and post-24 h incubation dissolved O2 and N2 concentrations. In most cases, we observed PO4, NH4, and N2 accumulation in bottom waters during stratification, along with O2 consumption. N2 accumulation, presumably due to denitrification, and water column O2 respiration rates varied and were not predictable based on temperature or nutrient treatment. Sediment O2 consumption and bottom-water NH4 and PO4 accumulation were generally higher in elevated nutrient and temperature mesocosms, but variability was high. In general, results followed expected patterns commonly observed in stratified lakes and reinforce previous work showing that internal nutrient loading from lake sediments includes both N and P, both of which represent nutrient legacies that can delay water quality improvements after watershed nutrient loading reductions.
09:45 AM
An integrated multiple driver mesocosm experiment reveals the effect of global change on planktonic food web structure (4677)
Primary Presenter: Cedric Meunier, Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI) (Cedric.Meunier@awi.de)
Global change puts coastal marine systems under pressure, affecting community structure and functioning. Here, we conducted a mesocosm experiment with an integrated multiple driver design to assess the impact of future global change scenarios on plankton, a key component of marine food webs. The experimental treatments were based on the RCP 6.0 and 8.5 scenarios developed by the IPCC, which were Extended (ERCP) to integrate the future predicted changing nutrient inputs into coastal waters. We show that simultaneous influence of warming, acidification, and increased N:P ratios alter plankton dynamics, favours smaller phytoplankton species, benefits microzooplankton, and impairs mesozooplankton. We observed that future environmental conditions may lead to the rise of Emiliania huxleyi and demise of Noctiluca scintillans, key species for coastal planktonic food webs. In this study, we identified a tipping point between ERCP 6.0 and ERCP 8.5 scenarios, beyond which alterations of food web structure and dynamics are substantial.
SS046A Mesocosm Based Experimental Studies to Address Challenges Emerging From Global Change on Stability of Aquatic Ecosystems
Description
Time: 8:30 AM
Date: 5/6/2023
Room: Auditorium Illes Balears