Natural systems are variable, and consequences of environmental variability have been increasing in relevance under climate change scenarios where not only changes in mean but also in variability patterns (magnitude, frequency, rate of change, interactions of multiple factors, etc) are expected. Motivated by such observed and predicted changes, investigations including or focusing on variability are accumulating. However, no common framework exists for approaching environmental variability research and the mismatches between theory and empirical data challenge our current understanding. In this session, we will contribute to a more integrated variability research by including studies that deal with relevant aspects of variability and propose how to approach variability from an experimental point of view while fostering integration with modelling approaches and experimental design aspects. Theoretical and experimental studies addressing the following aspects are highly welcome: (i) considering relevant terms of variability research including the components (characteristics) of variability and relevant types of multi-factorial interactions, (ii) applying relevant conceptual frameworks used for understanding the consequences of environmental variability in single and multifactorial scenarios, (iii) highlighting challenges for bridging theoretical and experimental studies involving simple to complex, closer-to-nature scenarios. With this session we aim to provide examples and a guide for future experimental efforts including how environmental variability experiments across different scales, degrees of control, and complexities can be combined according to their strengths and limitations.
Lead Organizer: Miriam Gerhard, Universidad de la República, Uruguay (miriam.libertad.gerhard@uni-oldenburg.de)
Co-organizers:
Apostolos-Manuel Koussoroplis, Université Clermont Auvergne, CNRS, Laboratoire Microorganismes Génome et Environnement, F-63000 Clermont–Ferrand, France; (a-manuel.koussoroplis@uca.fr)
Maren Striebel, Universität Oldenburg, ICBM (striebel@limnology.eu)
Alexander Wacker, Universität Greifswald (alexander.wacker@uni-greifswald.de)
Presentations
03:00 PM
Environmental variability across temporal scales – experimental assessments from organisms to communities (6532)
Primary Presenter: Christian Pansch, Abo Akademi University (ch.pansch@gmail.com)
Environmental variability is found across earth systems in local, regional, and global drivers. Variability occurs at diverse temporal and spatial scales, occasionally leading to unpredictable extremes. This talk illustrates the variability of multiple drivers in a coastal marine system, the significance of the timing of extreme events, and provides insights into how species can cope with, and potentially benefit from, environmental variability in a climate change context. We highlight the responses of the widespread ectotherm filter feeder Mytilus edulis to diurnal variability across thermal gradients, prevalent pattern in shallow coastal habitats. In a 5-weeks experiment, variability amplified thermal stress at average summer temperatures but acted as a temporal refuge during heatwave conditions. We conducted short-term lab assays to test for capacity for suppression and recovery of feeding and respiration in response to immediate thermal stress. We finally generated short-term thermal metabolic performance curves to explain growth responses observed in the long-term experiment. In a long-term mesocosm study, we show extremely warm conditions to select rare recruits capable of expressing increased metabolic suppression and recovery in response to daily fluctuations. These findings will be discussed in the framework of how environmental variability can provide temporal (and spatial) refugia, and how short-term metabolic assays, combined with theoretical frameworks, can predict long-term effects, and we highlight the significance heat selection in ectothermic populations.
03:15 PM
TEMPERATURE DEPENDENCE OF RESOURCES REQUIREMENTS IN FRESHWATER PHYTOPLANKTON. (5786)
Primary Presenter: Sarah Levasseur, Eawag - Swiss Federal Institute of Aquatic Science and Technology (sarah.levasseur@eawag.ch)
The effects of warming on populations and communities are currently central research topics in ecology and evolution. However, warming will not occur in isolation from other abiotic environmental changes. Therefore, it is important to consider how these factors may interact with warming. There is a lack of a mechanistic understanding of how temperature and resource availability interact and shape communities. Using phytoplankton, a key component of all aquatic ecosystems, I aim to investigate if the temperature-sensitivities of resource-use traits are conserved across the tree of life or if they differ systematically among taxonomic or functional groups. Furthermore, I will evaluate if the temperature dependence of resource-use traits is fixed for individual species. For this purpose, 20 phytoplankton species from four Swiss lakes were isolated. I then performed resource requirement experiments according to Tilman's framework (<em>R*</em> experiments), growing these species in 48 different conditions in which we manipulated one of three resources - nitrogen, phosphorus, and light, and temperatures – from 15°C to 35°C. The preliminary results show for every species, a temperature dependence on resource-use, usually, it is an increase of the resource requirements with temperature. However, these results do not show a general pattern that we can associate with functional groups for example. The change in resource requirements caused by warming may lead to modified competitive hierarchies, and thereby alter the outcome of competition in phytoplankton communities.
03:30 PM
Effects of fluctuating temperatures on phytoplankton are modulated by light and nutrient availability (7019)
Primary Presenter: Anna Lena Heinrichs, University Oldenburg, ICBM Wilhelmshaven (anna-lena-heinrichs@t-online.de)
Understanding how multiple resources (such light and nutrients) interact with temperature and affect organismal performance is challenging, especially in variable environments. Depending on organismal thermal traits, different performances are expected under fluctuating and constant temperature regimes. These differences between constant and fluctuation conditions might be determined by the availability of resources, as resource availability can influence thermal traits of organisms. In this study, we investigated how the temperature sensitivity of phytoplankton is influenced by multiple resource combinations of light and nutrients, under constant as well as fluctuating temperatures. We exposed the species Scenedesmus armatus to gradients of light intensity and nutrient concentrations (nitrogen and phosphorus) and investigated the effect of three temperature fluctuation scenarios (same frequency and amplitude, but fluctuations around different means). We compared the obtained results with outcomes measured under constant temperature conditions at the different combinations of nutrient and light supply. In both constant and fluctuating temperature scenarios, we found interactive effects of temperature, light and nutrients on growth rates. Differences in performance between constant and fluctuating temperatures with the same mean were influenced by the effect of light and nutrients. This study highlights the importance of considering multiple factors for ecological outcome predictions and showed that effects of fluctuations depend on organismal thermal niche.
03:45 PM
Growth and stoichiometry of Antarctic phytoplankton in response to interactions of fluctuating temperature and nutrient supply (5769)
Primary Presenter: Christoph Plum, University of Oldenburg (c.plum@uni-oldenburg.de)
Phytoplankton performance is influenced by environmental variation at multiple scales. However, experimental information on the response to multifactorial variation is still limited, particularly for polar environments. We investigated the response in maximum growth rate (r<sub>max/sub>), biomass and stoichiometry of an assembled community consisting of three Antarctic phytoplankton species from key groups exposed to a 5 x 5 gradient of nitrogen (N) and phosphorus (P) supply combined with two amplitudes of temperature fluctuation (± 0.5 and 1°C) around two different means (2°C and 5°C). Overall, phytoplankton growth rate and biomass was higher with increased N and P supply, indicating co-limitation of both nutrients. Biomass and growth rate decreased at elevated mean temperature under imbalanced nutrient supply conditions, indicating strong interactive effects of warming and nutrient conditions (ratios). At 2 °C, higher amplitude resulted in higher growth rate and biomass compared to low amplitude. At 5°C, increased amplitude resulted in lower growth and biomass at suboptimal N conditions. Phytoplankton N:P followed the supply ratio but decreased with increasing mean temperature and higher amplitude at N:P > 40. Overall, our results indicate that increasing thermal fluctuation (amplitude) around an increasing mean will push polar phytoplankton closer to their maximum thermal tolerance. Balanced nutrient conditions may compensate for the negative effect but under suboptimal nutrient supply, this may result in decreasing primary production and altered community composition.
04:00 PM
RESPIRATION AND INGESTION RATES OF THE BRACKISH MYSID NEOMYSIS INTEGER DURING A DAILY THERMAL FLUCTUATION CYCLE (6589)
Primary Presenter: Konstanze Bergunder, University of Greifswald (konstanze.bergunder@uni-greifswald.de)
Benthopelagic mysids play an important role in coastal ecosystems. The mysids can experience high thermal variability on short time scales particularly in shallow waters, forcing them to permanently adjust their metabolism. Respiration rates are directly influenced by temperature, whereas ingestion rates might additionally be influenced by behavioral aspects. We aim to understand how respiration and ingestion rates respond to temperature changes during a diurnal thermal fluctuation cycle and how both processes are linked. Neomysis integer was collected in a littoral zone of the Baltic Sea. After laboratory acclimation, mysids were exposed to either a constant temperature of 15°C or a daily temperature fluctuation of 15±5°C. Short-term respiration and ingestion rates were measured at four equidistant time points within 24 hours. Under constant temperature, respiration and ingestion rates of mysids did not differ among time points. However, in the fluctuating treatment both rates showed significant differences among time points. Respiration was highest at the thermal maximum and lowest at the thermal minimum. Ingestion rates showed the opposite pattern. When temperature transited the average, the direction of temperature change was crucial for the animals‘ response in respiration and ingestion rates. Our results suggest that even though respiration is instantaneously affected by temperature, it is additionally influenced by the previously experienced direction of thermal change. Ingestion appears to be decoupled from respiratory performance in likely stressful conditions.
04:15 PM
Transgenerational effects and associated changes in gene expression on sexual reproduction in the rotifer Brachionus plicatilis in relation to the habitat environmental predictability (5674)
Primary Presenter: Noemi Colinas Vallejo, University of Valencia (noemi.colinas@uv.es)
Understanding the processes enabling adaptation to time-varying environments is critically relevant in evolutionary ecology. A way to cope with environmental fluctuations where predictable conditions affect several generations is through non-genetic transgenerational effects. Sexual reproduction in rotifers is inhibited in several generations after diapause, but no study relating this transgenerational effect to environmental predictability has been done, its molecular basis being also unknown. Hence, we studied (1) the proportion of sexual reproduction (PSR) along successive clonal generations from diapausing eggs in eight Brachionus plicatilis populations inhabiting ponds with different levels of environmental predictability, and (2) the expression level of genes related to sex in rotifers (17-β-estradiol dehydrogenase, edh) and epigenetic signaling mechanisms (DNA methyltransferase, dnmt) in a subset of populations in our study system. Results show that clones from more predictable ponds were unresponsive to sex-inducing cues for a higher number of generations after leaving diapause. Instead, clones from more unpredictable ponds did respond to sex-inducing cues from early generations, likely to ensure diapausing egg production. Besides, edh increased its expression across generations and correlated positively with PSR, suggesting that edh is involved in the manifestation of sex. Differences were neither found in the expression of dnmt among generations nor between populations, pointing out that methylation may not be involved in the observed transgenerational effect.
SS091 Environmental Variability in a Multi-Factorial World: Connecting Experiments With Theory in Aquatic Systems
Description
Time: 3:00 PM
Date: 5/6/2023
Room: Sala Ibiza B