Ocean acidification (OA) and warming represent two of the greatest challenges of the 21st century, and understanding how they will influence whole ecosystems and their functionality is crucial for effective management. My goal was to determine how climate change affects species and community assemblages by investigating both direct (physiological responses), and indirect (species interactions) effects. In Chapter 2, a metaanalysis was presented that suggested there are ‘winners’ and ‘losers’ in climate change, alongside some predictable trait-based variation in sensitivity/resilience that can be attributed to taxonomic groups and/or life stages. Importantly, it was also demonstrated that the combination of OA and warming generally interacted synergistically. In the first experiment (Chapter 3), aquarium-based mesocosms (also used in Chapters 4 and 5) were used to demonstrate that OA and warming not only directly alter species (individual) physiological performance, but also their predator-prey dynamics due to the reduction of prey quality. It was found that the reduced prey quality was sufficient enough to prevent the predator from being able to initiate compensatory feeding, and they subsequently exhibited tissue loss. This highlights the need to simultaneously consider the inclusion of those species that are trophically linked. In Chapter 4, the role of the predator in eliciting non-consumptive effects (i.e. foraging-refuge trade-off) was additionally considered. The results suggest that future ocean acidification and warming govern the diminishing energy budget of consumers, which requires them to be less risk adverse, but ultimately more susceptible to predation themselves. As a consequence, the strength of non-consumptive effects appear to reduce as energy reserves are exhausted, and the behavioural choices of the organisms become driven instead by the need to reduce starvation risk. In Chapter 5, the effects of OA and warming on a biodiversity-ecosystem functioning relationship were tested. In general, it was found that increased biodiversity appeared to either promote or at least sustain ecosystem multi-functionality (i.e. the positive functioning of the ecosystem, across several ecosystem processes). However, when the temperature was elevated it was no longer possible to sustain this multi-functionality due to a shift towards heterotrophy, resulting in trade-offs between ecosystem processes. In Chapter 6, the longer-term consequence of OA were considered, and an in-situ CO2 seep site was used to empirically link the energetic consequences of the individual to the contemporary demographic processes of the population. The results suggest that ocean acidification is driving individual and population level changes that will alter eco-evolutionary trajectories. Moreover, the results also suggest that the altered population demographics will leads to greater levels of short-term genetic drift that is predicted to oppose adaptation. Overall, these results illustrate how the effects of future OA and warming are likely to have important individual-, population-, community- and ecosystem-level consequences, with further interactions between these levels of biological hierarchy. Achieving a more holistic understanding of these response is imperative for the adaptation and management of climate change.
Thesis, 22 MB, PDF
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Thesis, 22 MB, PDF
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