Abstract
In the last decade, the ‘Cumulative Pressure and Impact Assessment’ (CPIA) approach emerged as a tool to map expected impacts on marine ecosystems. However, CPIA assumes a linear response of ecosystems to increasing level of cumulative pressure weighting sensitivity to different anthropogenic pressures through expert judgement. We applied CPIA to Mediterranean coralligenous outcrops over 1000 km of the Italian coastline. Extensive field surveys were conducted to assess the actual condition of coralligenous assemblages at varying levels of human pressure. As pressure increased, a clear shift from bioconstructors to turf-dominated assemblages was found. The linear model originally assumed for CPIA did not fit the actual relationship between expected cumulative impact versus assemblage degradation. A log-log model, instead, best fitted the data and predicted a different map of cumulative impact in the study area able to appreciate the whole range of impact scenarios. Hence, the relative importance of different drivers in explaining the observed pattern of degradation was not aligned with weights from the expert opinion. Such findings stress the need for more incisive efforts to collect empirical evidence on ecosystem-specific responses to human pressure in order to refine CPIA predictions.
Highlights
Worldwide, marine coastal systems are threatened by increasing human pressures often acting simultaneously[1]
We applied the cumulative pressure and impact assessment (CPIA) framework on Mediterranean coralligenous outcrops over 1000 km of coast (Apulia, SE Italy), combining, for the first time, detailed information on human pressures and maps of habitat distribution with an extensive field survey to directly assess the state of coralligenous assemblages at varying levels of human pressure
The use of thresholds from the best fitting model based on actual data allowed us to discriminate the whole range of impact classes and, depicting a general condition of low impact to other cumulative impact assessments on the same habitat in the Mediterranean Sea (e.g.22), highlighted the presence of very highly impacted cells deserving management priority
Summary
Marine coastal systems are threatened by increasing human pressures often acting simultaneously[1]. The need for a deeper understanding of the effects of multiple stressors on ecosystems was highlighted about twenty years ago[4] and is still considered one of the most challenging questions for ecosystem-based management[5] In this framework, environmental impact assessments have attempted to move from considering single-source of impact towards more comprehensive approaches investigating ecological responses to multiple interacting human disturbances[6]. The aim of this study is to understand the relationship between human pressures and this priority habitat at regional scale, addressing two of the most relevant sources of uncertainty in CPIA: (i) the assumption of a linear relationship between the estimated cumulative impact and the actual condition of the investigated assemblages, and (ii) the relation between pressure weights from expert opinion and actual correlations among pressures and assemblage responses. The outcomes are expected to shed light on factors affecting the effectiveness of the CPIA approach to provide reliable estimates of potential effects of multiple anthropogenic pressures, contributing to inform spatial management of cumulative impacts on marine systems
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