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
05:00 PM
RESISTANCE AND RESILIENCE GOVERN THE FUNCTIONAL RESPONSES OF PLANKTON COMMUNITIES TOWARD CONSECUTIVE MARINE HEATWAVES IN MEDITERRANEAN COASTAL WATERS (4957)
Primary Presenter: Tanguy Soulié, CNRS (tanguy.soulie@gmail.com)
The frequency of marine heatwaves (HWs) is projected to increase in the Mediterranean Sea in the next decades. It is still unclear how consecutive HWs affect coastal plankton communities and their functions within ecosystems. In this regard, an in situ mesocosm experiment was performed in a Mediterranean lagoon for 33 days. Three mesocosms were used as controls following the natural temperature of the lagoon, while in three others two HWs of +5°C compared to the controls were applied from experimental day (d) 1 to d5 (HW1) and from d11 to d15 (HW2), while their temperature was similar to the controls during non-HW periods. High-frequency (every 1 min) data of dissolved oxygen, chlorophyll-a (chl-a), temperature, salinity and light from sensors immersed in all mesocosms were used to calculate gross primary production (GPP), respiration (R) and phytoplankton growth (µ) and loss (L) rates. Nutrients, photochemical quantum yield and phytoplankton community structure from pigments were also sampled and analyzed. HW1 significantly increased by 7 to 38% GPP, R, chl-a, µ and L. HW2 shifted the system toward heterotrophy by only enhancing R. Normal phytoplankton succession from diatoms to haptophytes was altered by both HWs as cyanobacteria and chlorophytes were favored at the expense of haptophytes. These results indicate that HWs have important effects on Mediterranean plankton communities and that their resistance and resilience during and after a first HW attenuate the effects of a second HW on phytoplankton processes, but not on R which was strongly regulated by temperature.
05:15 PM
WARMING AMPLIFIES A TROPHIC CASCADE IN A COASTAL FOOD WEB (4966)
Primary Presenter: Tiina Salo, Åbo Akademi (tsalo@abo.fi)
The combined anthropogenic pressures of predator loss and warming challenge our understanding of ecosystem function. Predator effects cascade down food webs via predator-prey interactions while warming increases metabolic rates, suggesting that climate change effects interact with predators and their prey through consumer processes. However, the direction of effects will depend on both the food web structure and the ability of the consumers to adapt to changing temperatures. We tested the interactive effects of predator loss and warming on trophic interactions by conducting a mesocosm study, using a simplified shallow coastal food web as a model system. We included three trophic levels (predators: three-spined stickleback, Gasterosteus aculeatus; grazers: gastropods, amphipods, and isopods; and macroalgal foundation species: Fucus vesiculosus and F. radicans) and two temperature treatments (ambient and +4° C) to assess how predators and warming altered traits at each trophic level. Predator removal modified grazer trait responses to warming, and this effect cascaded further down the food web. Warming and predator presence together reduced crustacean biomass and increased diatom biomass. Predator removal increased the survival and recruitment of crustaceans but decreased gastropod biomass. The results illustrate that warming and predator loss impact both food web dynamics and traits at different trophic levels.
05:30 PM
Effects of CO<sub>2</sub>-equilibrated OAE on primary production rates and plankton metabolic balance in an oligotrophic system - a mesocosm approach (7025)
Primary Presenter: Laura Marin-Samper, Universidad de Las Palmas de Gran Canaria (laura.marin@ulpgc.es)
Ocean Alkalinity Enhancement (OAE) is one of the Negative Emissions Technologies (NETs) with the highest climate mitigation potential. Yet, despite its potential to enhance long-term carbon storage in ocean water as bicarbonate ions, and therefore to mitigate ocean acidification, little is known about its possible side effects and/or co-benefits on natural planktonic communities. To address this knowledge gap, a mesocosm experiment was carried out in the Taliarte Harbor, on Gran Canaria, Spain. Nine mesocosms were deployed and a CO<sub>2</sub>-equilibrated alkalinity gradient was applied in increments of 300 µEq · L<sup>-1</sup>, from 2400 to 4800 µEq · L<sup>-1</sup>. This mesocosm study was the first attempt at evaluating OAE’s potential impacts <em>in situ</em>. The metabolic response of the microbial plankton community was monitored from mid-September to mid-October 2021. The results show that Net Community Production (NCP) and Gross Community Production (GCP) rates, as well as Community Respiration (CR) and metabolic balance (GP: R), did not present a linear response to the applied TA gradient. Yet, a non-significant optimum curve was observed in the form of a slight increase in all rates up to &Delta1800 µEq · L<sup>-1</sup>, followed by a drop. In fact, phytoplankton blooms were observed in the &Delta1500 and &Delta1800 µEq · L<sup>-1</sup> treatments where, from a heterotrophic balance state, NCP rates increased to 4 and 8 µmol O<sub>2</sub> · kg<sup>-1</sup> · d<sup>-1</sup>, respectively. These blooms and the optimum curve were also reflected in the size fractionated chlorophyll a and 14C uptake data. More specifically in the total chlorophyll a concentration, Particulate Organic Carbon (POC in µg of 14C · m<sup>-3</sup> · d<sup>-1</sup>) and total organic carbon (POC+DOC) production through 14C uptake, in both parameter’s 2-20 µm size-fraction, but also in the nanoeukaryotic abundance data obtained through flow cytometry. Lastly, abiotic precipitation occurred in the highest TA treatment (&DeltaTA 2400 µEq · L<sup>-1</sup>) after day 18, but no effect on the metabolic rates measured was detected. In summary, a damaging effect of CO<sub>2</sub>-equilibrated alkalinity enhancement, in the range applied here, on the microbial plankton community, in terms of its production and respiration rates, cannot be inferred from this study. Nonetheless, additional experimental work is necessary to reject a non-linear response and to further understand the effects of OAE, both short and long term, on the planktonic community.
05:45 PM
TESTING APPLICABILITY AND STABILITY OF OCEAN ALKALINITY ENHANCEMENT UNDER DIFFERENT DEPLOYMENT METHODS IN DIFFERENT PELAGIC ENVIRONMENTS (6434)
Primary Presenter: Julieta Schneider, GEOMAR (jschneider@geomar.de)
Ocean Alkalinity Enhancement (OAE) is a negative emissions technology that aims to chemically sequester CO2 in the ocean while also counteracting ocean acidification. Yet, experimental work to guide potential implementation at scale is scarce. To address knowledge gaps surrounding durability and application methods in close-to-natural conditions, <em>in situ</em> mesocosm experiments were conducted in subtropical and temperate pelagic ecosystems. In both, we simulated OAE scenarios in a gradient approach and regularly monitored the carbonate system for 30 and 48 days after adding alkaline solutions. In the subtropical experiment, a CO2-equilibrated approach with 0-2400 umol Kg<sup>-1</sup> of added Total Alkalinity (TA) was implemented to focus on whether the added alkalinity and associated sequestered carbon remained in the system. In the temperate experiment, a non-equilibrated approach with 0-600 umol Kg<sup>-1</sup> added TA was used to observe and follow the ingassing of CO2. We found that TA was stable over time in both ecosystems, except for the highest +2400 umol Kg<sup>-1</sup> treatment, in which alkalinity loss via secondary precipitation of aragonite started to occur 12 days after manipulation. Furthermore, an increase in DIC associated with CO2 uptake was barely observed in the non-equilibrated set-up for the timeframe of the experiment. Here we will discuss these equilibrated and non-equilibrated deployment methods of OAE in natural settings and their potential implications for deployment at scale.
06:00 PM
EFFECTS OF OCEAN ALKALINITY ENHANCEMENT ON ZOOPLANKTON COMMUNITY: TWO TEMPERATE MESOCOSM STUDIES (6862)
Primary Presenter: Amrita Bhaumik, Alfred Wegener Institute, Helmoholtz Center for Polar and Marine Research (amrita.bhaumik@awi.de)
Ocean alkalinity enhancement (OAE), has been put forward as a potential technique to reduce atmospheric CO2 levels. OAE accelerates the natural rock weathering process by adding alkaline minerals directly into seawater. However, sudden alterations in seawater pH and alkalinity might shift the plankton community structure. Unfortunately, the impacts of OAE on marine ecosystems, especially zooplankton, are mostly unexplored. The present study assessed the direct (physiological stress) and indirect (changes in phytoplankton dynamics) effects of increased alkalinity and pH on the zooplankton community. Natural plankton communities were studied during two large-scale mesocosm experiments under simulated OAE conditions in a Norwegian fjord and at Helgoland roads in the North Sea. In the fjord, an alkalinity gradient from delta 0 to 600 µEql-1 was tested and a comparative analysis was conducted between calcium and silica mineral-based OAE set-ups. In contrast, only calcium-based mineral was used in Helgoland Road with a higher range of alkalinity levels, ranging from delta 0 to 1500 µEql-1 . We assessed the zooplankton community composition in both studies. The results were corroborated with laboratory experiments, using cosmopolitan copepod species Acartia tonsa¸ where no direct effects of increased alkalinity were observed, suggesting their relative resiliency toward altered OAE. Overall, our study emphasized the importance of a multitrophic study of marine communities to understand the potential ecological consequences of emerging techniques such as OAE.
06:15 PM
OCEAN ALKALINITY ENHANCEMENT THROUGH ENHANCED SILICATE WEATHERING IN COASTAL AREAS: A LONG-TERM MESOCOSM STUDY (6313)
Primary Presenter: Astrid Hylén, University of Antwerp (astrid.hylen@uantwerpen.be)
Methods for removing CO2 from the atmosphere are urgently needed to keep the global temperature increase below 1.5°C. A promising CO2 removal technology is enhanced silicate weathering (ESW) in coastal systems. The technology is based on natural silicate mineral weathering, which releases alkalinity and thereby increases the seawater’s capacity to dissolve CO2. It is though that silicate weathering can be sped up by introducing the minerals in coastal sediments where waves, currents and bioturbation can stimulate the weathering. Although model and laboratory studies suggest ESW is feasible, research on the process in natural conditions is lacking. Hence, the CO2 sequestration efficiency and risks when applying ESW in the field are largely unknown. We present results from the first and longest-running mesocosm experiment investigating ESW and associated CO2 uptake in coastal marine sediments. In tanks containing natural sediment, we have studied biogeochemical cycling after treatment with the fast-weathering silicate mineral olivine. Lugworms were added to some tanks to investigate the effect of bioturbation on the olivine dissolution rate and the impact of olivine addition on biota. Five years into the experiment, olivine dissolution is obvious from an elevated sedimentary alkalinity release and decreased average olivine grain size. The elevated alkalinity release has further led to higher CO2 sequestrations in tanks with olivine. Based on the results from this unique mesocosm setup, we discuss the large-scale effect of ESW on biogeochemical cycling in coastal ecosystems.
SS046E Mesocosm Based Experimental Studies to Address Challenges Emerging From Global Change on Stability of Aquatic Ecosystems
Description
Time: 5:00 PM
Date: 6/6/2023
Room: Auditorium Illes Balears