Investigating the impacts of multiple stressors on marine coastal ecosystems

Thesis

Coastal ecosystems are increasingly exposed to stressors across space and time, including global climate change and local pressures such as nutrient enrichment, pollutants, and habitat modification. Management and cumulative effects assessment often treat combined stressor effects as additive, despite growing recognition of interactive, context-dependent outcomes. This thesis couples in situ multiple stressor field experiments with decision-ready governance frameworks for coastal management. Using a passive warming manipulation (black versus white settlement plates) paired with local nutrient enrichment contrasts, Chapter 3 tests independent and interactive stressor impacts on a UK rocky shore through a summer time series and across multiple levels of biological organisation, from genes to populations. Responses span key invertebrate and algal functional groups, alongside trophic and transcriptomic indicators. Enrichment generally increased abundance and cover, whereas warming tended to depress them, and interaction signals were time-structured, most evident for barnacle abundance and cyanobacteria concentration, with synergistic interactions across individual dates and season-wide trends. Chapter 4 applies the same methodology across 22 international sites to estimate global mean effects and quantify cross-site heterogeneity. At the global scale, enrichment increased macroalgal cover and shifted barnacle abundance, while warming reduced both groups. Meta-regressions relate site-level sensitivities to abiotic covariates such as precipitation and air temperature variability, and path analyses indicate that macroalgae mediate a substantial component of indirect stressor effects across ecological communities. Building on this evidence of temporospatial context dependence and wider syntheses, Chapter 5 addresses the policy gap that multiple stressor science is rarely embedded in marine spatial planning and cumulative assessment. It proposes an eight component management framework integrating land–sea connectivity, blue economy trade-offs, stressor interaction logic, and adaptive monitoring triggers, operationalised through a Massachusetts case study. Collectively, the thesis shows how the context dependence of coastal multiple stressor impacts can be practically interpreted for transparent, adaptive, multi-sectoral governance across the science–policy interface.

Authors: Wilson, RO

• DOI: 10.5287/ora-eoozoo7o4
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: climate change; multiple stressors; experimental ecology; nutrient enrichment; rocky shores; field experiment; science-policy interface; marine ecosystems; marine spatial planning; context dependence; sewage pollution; land-sea interface; cumulative impacts; ecosystem-based management; stressor interactions; coastal ecosystems; blue economy; warming; intertidal ecology
• Subjects: Environmental policy; Global environmental change; Sewage pollution; Multiple stressors; Marine spatial planning; Ecology; Blue economy; Coastal ecology; Climate change; Experimental ecology; Marine biology