An understanding of risks to biodiversity is needed for planning action to slow current rates of decline and secure ecosystem services for future human use. Although the IUCN Red List criteria provide an effective assessment protocol for species, a standard global assessment of risks to higher levels of biodiversity is currently limited. In 2008, IUCN initiated development of risk assessment criteria to support a global Red List of ecosystems. We present a new conceptual model for ecosystem risk assessment founded on a synthesis of relevant ecological theories. To support the model, we review key elements of ecosystem definition and introduce the concept of ecosystem collapse, an analogue of species extinction. The model identifies four distributional and functional symptoms of ecosystem risk as a basis for assessment criteria: A) rates of decline in ecosystem distribution; B) restricted distributions with continuing declines or threats; C) rates of environmental (abiotic) degradation; and D) rates of disruption to biotic processes. A fifth criterion, E) quantitative estimates of the risk of ecosystem collapse, enables integrated assessment of multiple processes and provides a conceptual anchor for the other criteria. We present the theoretical rationale for the construction and interpretation of each criterion. The assessment protocol and threat categories mirror those of the IUCN Red List of species. A trial of the protocol on terrestrial, subterranean, freshwater and marine ecosystems from around the world shows that its concepts are workable and its outcomes are robust, that required data are available, and that results are consistent with assessments carried out by local experts and authorities. The new protocol provides a consistent, practical and theoretically grounded framework for establishing a systematic Red List of the world’s ecosystems. This will complement the Red List of species and strengthen global capacity to report on and monitor the status of biodiversity

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Abstract1. Along urbanised coastlines, urban infrastructure is increasingly becoming the dominant habitat. These structures are often poor surrogates for natural habitats, and a diversity of eco-engineering approaches have been trialled to enhance their biodiversity, with varying success.2. We undertook a quantitative meta-analysis and qualitative review of 109 studies to compare the efficacy of common eco-engineering approaches (e.g. increasing texture, crevices, pits, holes, elevations and habitat-forming taxa) in enhancing the biodiversity of key functional groups of organisms, across a variety of habitat settings and spatial scales.3. All interventions, with one exception, increased the abundance or number of species of one or more of the functional groups considered. Nevertheless, the magnitude of effect varied markedly among groups and habitat settings. In the intertidal, interventions that provided moisture and shade had the greatest effect on the richness of sessile and mobile organisms, while water-retaining features had the greatest effect on the richness of fish. In contrast, in the subtidal, small-scale depressions which provide refuge to new recruits from predators and other environmental stressors such as waves, had higher abundances of sessile organisms while elevated structures had higher numbers and abundances of fish. The taxa that responded most positively to eco-engineering in the intertidal were those whose body size most closely matched the dimensions of the resulting intervention. Synthesis and applications. The efficacy of eco-engineering interventions variesamong habitat settings and functional groups. This indicates the importance of developing site-specific approaches that match the target taxa and dominant stressors. Furthermore, because different types of intervention are effective at enhancing different groups of organisms, ideally a range of approaches should be applied simultaneously to maximise niche diversity. K E Y W O R D Sartificial structure, crevice, depression, eco-engineering interventions, habitat-forming species, microhabitat, protrusion, rockpool, seeding, urban infrastructure

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