Investigating the Impacts of Multiple Stressors on Marine Ecosystems

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Anthropogenic stressors, such as climate change and pollution, are rapidly eroding natural ecosystems (Orr et al., 2020; Kunze et al., 2021). Understanding the effects of these stressors is imperative for the prediction, management, and mitigation of impacts. Co-occurring stressors may have a combined, additive effect that is a predictable sum of their independent effects. However, non-additive effects, namely synergistic (stressors amplify each other) or antagonistic (stressors mitigate each other), are less predictable (Breitburg, B., Seitzinger, S. & Sanders, J., 1999; Côté, I., Darling, E. & Brown, C., 2016). Stressors may interact in different ways over time and space, changing their independent and combined effects on different levels of ecosystem organisation (Jackson et al., 2021).Multiple stressor impacts on marine benthic and intertidal ecosystems are understudied, despite the range of ecosystem functions and services they provide (Pansch & Hiebenthal, 2019). For instance, benthic ecosystems are vital in global carbon and nutrient cycling processes; and intertidal ecosystems often contain species living near their thermal limit, serving as an early indicator of climate change impacts (Helmuth et al., 2006; Kordas et al., 2014). These ecosystems face ubiquitous abiotic stressors such as upwelling and extreme tidal variability, making them particularly vulnerable to anthropogenic stressors, including warming and pollution (Waldbusser and Salisbury, 2014).However, multiple stressor research is often limited by two key shortcomings: 1) studies frequently assume stressors occur synchronously; 2) studies often quantify stressor effects on low levels of ecosystem organisation, such as survival or abundance (Jackson et al., 2021). Such shortcomings reduce the temporal and biological realism of multiple stressor research.Increasing global intensity of anthropogenic stressors necessitates that multiple stressor research must direct more attention to marine ecosystems. This is echoed by the UN Decade for Ocean Sciences and Decade of Ecosystem Restoration. My DPhil shall explore this research gap, with focus on benthic and intertidal ecosystems, and shall ensure greater temporal and biological realism than previous research. I aim to develop replicable methods for large-scale data collection, to propagate sustained, long-term attention to this area.