Abstract
Understanding the spatial distribution of human impacts on marine environments is necessary for maintaining healthy ecosystems and supporting ‘blue economies’. Realistic assessments of impact must consider the cumulative impacts of multiple, coincident threats and the differing vulnerabilities of ecosystems to these threats. Expert knowledge is often used to assess impact in marine ecosystems because empirical data are lacking; however, this introduces uncertainty into the results. As part of a spatial cumulative impact assessment for Spencer Gulf, South Australia, we asked experts to estimate score ranges (best-case, most-likely and worst-case), which accounted for their uncertainty about the effect of 32 threats on eight ecosystems. Expert scores were combined with data on the spatial pattern and intensity of threats to generate cumulative impact maps based on each of the three scoring scenarios, as well as simulations and maps of uncertainty. We compared our method, which explicitly accounts for the experts’ knowledge-based uncertainty, with other approaches and found that it provides smaller uncertainty bounds, leading to more constrained assessment results. Collecting these additional data on experts’ knowledge-based uncertainty provides transparency and simplifies interpretation of the outputs from spatial cumulative impact assessments, facilitating their application for sustainable resource management and conservation.
Highlights
Over 97% of the world’s oceans are exposed to multiple concurrent threats from human activities resulting in cumulative impacts[1], with the severity of these cumulative impacts increasing in recent years[2,3]
Mangroves notably differed from all other ecosystems because the most common cumulative impact scores recorded for this ecosystem occurred in the middle of the score range, as opposed to occurring close to the minimum score
There are drawbacks to using expert knowledge as a surrogate for quantitative empirical data, a key one being knowledge-based uncertainty[16] and the difficulty in accounting for it[21]. We demonstrate that this source of uncertainty can affect spatial cumulative impact assessments, and their interpretation, regarding the level of confidence to ascribe to mapped outputs
Summary
Over 97% of the world’s oceans are exposed to multiple concurrent threats from human activities resulting in cumulative impacts[1], with the severity of these cumulative impacts increasing in recent years[2,3]. The approach accounts for both the vulnerability of marine ecosystems to different threats[7] and the spatial exposure and intensity of each threat throughout a defined study area[1]. As such, this type of assessment can support integrated management approaches that monitor and counter multiple threats, rather than single threats in isolation[8,9,10]. A human activity or climatic perturbation, which is considered to be a threat to one or more of the eight ecosystems within the study area based on published research or expert knowledge[22]
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