The impact of multiple stressors on coastal biodiversity and associated ecosystem services
Abstract
Marine and coastal ecosystems are subject to diverse and increasingly intensive anthropogenic
activities, making understanding cumulative effects critically important. However, accurately
accounting for the cumulative effects of human impacts can be difficult, with the possibility of multiple
stressors interacting and having greater impacts than expected, compounding direct and indirect
effects on individuals, populations, communities and ecosystems. Assessment of multiple stressors
therefore requires extensive scientific research that directly tests how single or multiple ecological
components are affected by stressors, both singly and when combined, and as a consequence,
cumulative effects assessments are now increasingly included in environmental assessments.
Currently, there is a need to assess these at larger spatial scales, with additional research also urgently
needed on the responses of ecological components, processes and functions to single and cumulative
stressors. As cumulative environmental impacts could be better addressed by regional stressor effects
assessments that combine methods for predicting multiple pressures on ecosystem recovery
alongside degradation, this study used several separate approaches that can be used in parallel to give
support for local management measures. I tested four completely different methods – a range of
multi-metric indices, a food web model (Ecopath), a predictive model (Ecosim) and a Bayesian Belief
Network model. Each approach was tested and compared in two shallow water estuarine systems, in
Scotland and England, initially concerning the impact of nutrient enrichment and subsequent recovery
and was followed by an investigation of how the addition of multiple stressors (nutrient levels,
temperature and river-flow rates) would impact the future state of each system. The response to
stressors was highly context dependent, varying between and within geographic locations. Overall,
each of the four different approaches complemented each other and gave strong support for the need
to make big reductions in the pressures and to consider trade-offs between impacting pressures. The
models and tools also indicate that in order to reach an improved overall environmental state of each
ecosystem, a focus on nutrient reductions are likely to be the most effective of the controls on
stressors explored and that cumulative effects of the management of nutrient inputs and increased
water temperatures and river-flow are likely to exist.
Type
Thesis, PhD Doctor of Philosophy
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