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Climate change increasingly affects organisms and ecosystems. Temporary pools and their fauna may be severely impacted by predicted increased temperatures. Being typically shallow, water temperatures closely follow atmospheric temperatures. Furthermore, inundation lengths (i.e. hydroperiods) are dependent on evaporation and increased temperatures would result in reduced hydroperiods. Although specialist inhabitants of temporary pools, such as large branchiopod crustaceans, are often already adapted to deal with significant daily temperature fluctuations (DTF) and short growing seasons, especially in warm regions and short-lived systems, they may be at the limit of their adaptive capacity. We use three zooplankton species from different functional groups (Conchostraca, Anostraca and Ostracoda) from shallow temporary rock pools in South Africa as models and investigate if key life-history traits (e.g. life-span, fecundity, hatching, egg survival, CT max) will be sensitive to temperature increase and DTF as expected under climate change. Next to individual and species-level responses, we assess potential changes in biotic interactions among these three important species in temporary pool food-webs. Our results indicate changes in the water variables conductivity, turbidity and chlorophyll a concentration, in response to increased temperatures. With regard to life-history responses, increased temperatures led to decreases in body size, fecundity, survival and life span. Since species were differentially affected, biotic interactions among the studied species, which represent different functional groups, will likely change. This demonstrates the importance of including biotic interactions in climate change vulnerability assessments instead of only looking at species level responses. Our results also indicate the potential for acclimation and/or adaption by increased growth and maturation rate and increasing thermal tolerance. While egg bank persistence and bet hedging strategies will become even more important under climate change, these will potentially be negatively effected through reduced egg survival rates. Future studies should aim at even higher levels of ecological realism by working in larger volumes, including a full community and testing for interactive effects among temperature stress and other stressors such as increased CO2 levels and predator presence. Finally, by running studies across a longer time and additional growing seasons, the potential impact of long lasting transgenerational effects and (genetic) adaptation on population demographics in response to future environmental conditions could be tracked.

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Global change is a phenomenon impacting habitats worldwide, such as temporary ponds. Temporary ponds are ponds that are not permanently filled with water, but have re-occurring dry periods. They form an essential part of ecosystems, among others, because of the services they deliver, such as aiding the carbon cycling an being a small scale water supply. However, despite their importance, these ecosystems remain poorly understood, and their protection from human-related change is often ignored. In this study, we try to improve our understanding of the long term effects of global warming and an overuse of nutrients (a phenomenon called eutrophication), and furthermore study the role of killifish as top predators in temporary pond food chains under human-related stress. The reason we are studying these killifish is because they are one of the only fish species capable of surviving the dry season of these ponds, and therefore one of the only fish species co-occurring with large zooplankton. We conducted a series of laboratory experiments under controlled conditions to study the functioning of temporary African savannah ponds and their inhabitants to realistic scenarios of increasing temperature and eutrophication. Our results indicate that both climate change and eutrophication impact numerous important environmental factors, such as conductivity and pH. Additionally, pond communities were also affected by climate change and eutrophication. Some of these effects were positive, such as the impact of an increased temperature on the number of zooplankton individuals, while others were negative, including a reduced number of plants caused by eutrophication. Important to note is that not all effects were immediately visible, some only became noticeable during the later stages of our experiment. This demonstrates how important it is to test for exposure to global change over ecologically relevant time scales. The presence of fish appears to impact all temporary pond characteristics. These effects are noticeable both on primary productivity as well as on life history traits and behavioural traits. Life history traits include, for example, hatching and body size, and behavioural traits include height use and activity. Likely, both life history traits and behavioural traits are adapted to the presence of fish, as part of anti-predator strategies. This pioneering work is an important step towards improved understanding of the impact of fish predators on temporary pond communities in a context of global warming.

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Pollution is a key environmental problem and a major contributor to global change. Ecotoxicology combines ecology and toxicology to study the effects of pollutants on organisms and ecosystems as a whole, in an attempt to mitigate deleterious effects of environmental pollution. To determine the environmental safety of a chemical compound and to promote the sustainability of ecosystems, ecotoxicological studies use a battery of standardised short-term exposure tests to assess harmful, stressful or lethal effects of pollution on study organisms. Such tests are performed on different types of organisms and rapidly provide valuable data for regulatory decision making but are often offset by a low ecological relevance. Moreover, more subtle behavioural effects are not assessed despite having direct and indirect ecological consequences. Therefore, and although safety margins are adopted, environmental risks of pollutants may not be correctly estimated. This is especially true for emerging contaminants such as pharmaceutical compounds. To advance the assessment of risks associated with such pollutants, standardised tests to quantify sub-lethal behavioural effects over ecologically relevant time periods are needed. However, such tests are not compatible with the relatively long lifespan of traditional vertebrate model organisms.In this thesis, we explore the potential of the short-lived Turquoise killifish Nothobranchius furzeri as a vertebrate model for behavioural studies, specifically with regard to ecotoxicological testing of whole-life and multigenerational exposure to persistent contaminants.Firstly, we studied what constitutes normal behaviour in N. furzeri to characterise its behavioural baseline in Chapter 1, 2 and 3. We found intrinsic behavioural variation in multiple traits at the population- and individual level, and N. furzeri males and females were shown to be dissimilar in their behavioural profile. In addition to intrinsic behavioural variation, we also showed that conditions of the rearing environment shape the development of behaviour in N. furzeri. These findings are directly relevant for animal welfare as well as for the development of optimised husbandry- and experimental protocols for behavioural studies in ecotoxicology with N. furzeri.We then performed single-stressor exposure studies on N. furzeri with fluoxetine as a common neuroactive pharmaceutical pollutant, starting with a short-term exposure assay (Chapter 4) and advancing to a more ecologically relevant exposure regime (Chapter 5). Finally, we performed a multigenerational mixed-stressor exposure study (Chapter 6) on sensitive life-history and behavioural endpoints to incorporate higher levels of ecological realism. Not only did we show that exposure to a neuroactive contaminant induced both behavioural and life-history alterations in N. furzeri, but we also demonstrated that mixed-stressor exposure studies over multiple generations are needed and possible in a time- and cost-efficient way when using N. furzeri as a model.Overall, our results contribute to an increased understanding of N. furzeri behaviour and demonstrate the potential of N. furzeri as a model organism to advance ecotoxicological assessment.

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Wetlands are unique ecosystems defined by their saturation with water, either year-round or during certain seasons. Wetlands provide many benefits to humanity. They provide many resources, act as natural buffers during heavy rainfall by helping to control floods and house a wide diversity of unique species of animals and plants. Additionally, wetlands play an important role in storing carbon and act as natural filters for water, purifying it as it flows through. Unfortunately, human activities pose a significant threat to wetlands, making conservation efforts essential. Freshwater ecosystems like wetlands are inhabited by a diverse variety of organisms, including macroinvertebrates. These organisms can be easily observed with the naked eye. Among them are familiar species like snails, beetles, worms, and many others. This study delves into the world of macroinvertebrates, along with the environmental conditions of the ponds they inhabit. We subdivided the organisms according to their food preferences and resources, which is referred to as ‘functional feeding groups’. Functional feeding groups were examined across five study areas in Flanders: Grenspark Kalmthoutse Heide, De Zegge, Olens Broek, Nieuwpoort, and Bokrijk. In these areas, a selection of ponds was sampled for macroinvertebrates and the environmental conditions in which these organisms live. Samples were collected in all five areas during autumn. For Grenspark Kalmthoutse Heide, De Zegge, and Olens Broek, a second round of sampling was also done in spring. The groups we divided our macroinvertebrates into were: scrapers, shredders, gathering collectors, filtering collectors, and predators. Shredders consume both living and dead plant material. Gathering collectors feed on smaller organic particles on substrates in the water, while filtering collectors filter organic particles directly from the water column. Predators prey on other living animals, and scrapers graze on organic matter on substrates like submerged plant material or rocks. During the analysis, the environmental conditions for each area were examined and used to try and explain variation in resident functional groups. Overall, pH and nutrient levels emerged as important structuring environmental factors. More acidic systems were typically dominated by predatory taxa such as water beetles and had few scrapers such as snails. High nutrient loading seemed to drive a shift towards gathering collectors. Functional feeding groups can provide useful information about the condition of ponds. It is a useful tool to learn about the ecological integrity of freshwater systems since the approach is quick and organisms should not always be identified to the species level. However, monitoring and managing wetland ecosystems should rely on an integrated approach.