Human actions challenge nature in many ways. Ecological responses are ineluctably complex, demanding measures that describe them succinctly. Collectively, these measures encapsulate the overall 'stability' of the system. Many international bodies, including the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, broadly aspire to maintain or enhance ecological stability. Such bodies frequently use terms pertaining to stability that lack clear definition. Consequently, we cannot measure them and so they disconnect from a large body of theoretical and empirical understanding. We assess the scientific and policy literature and show that this disconnect is one consequence of an inconsistent and one-dimensional approach that ecologists have taken to both disturbances and stability. This has led to confused communication of the nature of stability and the level of our insight into it. Disturbances and stability are multidimensional. Our understanding of them is not. We have a remarkably poor understanding of the impacts on stability of the characteristics that define many, perhaps all, of the most important elements of global change. We provide recommendations for theoreticians, empiricists and policymakers on how to better integrate the multidimensional nature of ecological stability into their research, policies and actions.

Ecological stability is touted as a complex and multifaceted concept, including components such as variability, resistance, resilience, persistence and robustness. Even though a complete appreciation of the effects of perturbations on ecosystems requires the simultaneous measurement of these multiple components of stability, most ecological research has focused on one or a few of those components analysed in isolation. Here, we present a new view of ecological stability that recognises explicitly the non-independence of components of stability. This provides an approach for simplifying the concept of stability. We illustrate the concept and approach using results from a field experiment, and show that the effective dimensionality of ecological stability is considerably lower than if the various components of stability were unrelated. However, strong perturbations can modify, and even decouple, relationships among individual components of stability. Thus, perturbations not only increase the dimensionality of stability but they can also alter the relationships among components of stability in different ways. Studies that focus on single forms of stability in isolation therefore risk underestimating significantly the potential of perturbations to destabilise ecosystems. In contrast, application of the multidimensional stability framework that we propose gives a far richer understanding of how communities respond to perturbations.

Kelp forests along temperate and polar coastlines represent some of most diverse and productive habitats on the Earth. Here, we synthesize information from >60 years of research on the structure and functioning of kelp forest habitats in European waters, with particular emphasis on the coasts of UK and Ireland, which represents an important biogeographic transition zone that is subjected to multiple threats and stressors. We collated existing data on kelp distribution and abundance and reanalyzed these data to describe the structure of kelp forests along a spatial gradient spanning more than 10° of latitude. We then examined ecological goods and services provided by kelp forests, including elevated secondary production, nutrient cycling, energy capture and flow, coastal defense, direct applications, and biodiversity repositories, before discussing current and future threats posed to kelp forests and identifying key knowledge gaps. Recent evidence unequivocally demonstrates that the structure of kelp forests in the NE Atlantic is changing in response to climate- and non-climate-related stressors, which will have major implications for the structure and functioning of coastal ecosystems. However, kelp-dominated habitats along much of the NE Atlantic coastline have been chronically understudied over recent decades in comparison with other regions such as Australasia and North America. The paucity of field-based research currently impedes our ability to conserve and manage these important ecosystems. Targeted observational and experimental research conducted over large spatial and temporal scales is urgently needed to address these knowledge gaps.

with the proliferation of coastal defences. This is an adaptation option (sensu IPCC 2014) that has been adopted worldwide to protect the growing coastal population and its property, transport infrastructure, industry and commerce, as well as valuable amenity and recreational areas (for review, see chapters in Burcharth et al. 2007, Zanuttigh et al. 2014). In this review, we discuss current evidence and thinking on biodiversity and ecosystem responses to global drivers of change, with a focus on recent rapid climate change and its interaction with regional and local impacts due to 'ocean sprawl'-the proliferation of artificial structures in the sea. We consider how efforts to combat climate change, such as mitigation via offshore renewables ('green' energies to reduce CO 2 emissions), and adaptation via sea defences are leading to a proliferation of artificial structures, resulting in changes in the proportion of hard versus soft coastal habitats, the distribution of species, assemblage composition, and community structure. We also discuss the role of coastal development, including ports and other transport infrastructure as well as offshore structures (e.g., oil and gas platforms), in altering coastal and marine ecosystem structure and functioning. Finally, we undertake a critical review of the current 'state of the art' in the emerging field of 'green engineering', which combines environmentally conscious attitudes, values, and principles with science, technology, and engineering practice, all directed towards improving local and global environmental quality. Our scope is the global coastline extending vertically to the uppermost extent of tidal influence, with particular emphasis on open coasts and offshore structures that have seen the most research. This is in contrast to the freshwater tidal reaches of estuaries, which have received little attention (but see Francis & Hoggart 2008, 2009, Hoggart et al. 2012). Many of the case studies and examples are drawn from temperate systems in developed countries, reflecting the experience of the authors and the distribution of published research. Two themes permeate our review: firstly, how ecosystem services are at risk from modification of the coast by artificial structures; secondly, the interaction between the provision of new 'hard' substratum as a societal adaptation response, resulting in altered habitat connectivity and changes in the distribution of species and composition of assemblages. We conclude by identifying current knowledge gaps and future research needs. Burgeoning coastal human populations The diversity of coastal habitats includes rocky shores, sandy and muddy beaches, barriers, spits and sand dunes, estuaries and lagoons, deltas, wetlands, and coral reefs. These individually and K27072_C004.indd 190 6/15/16 12:57 PM 191 OCEAN SPRAWL collectively provide a disproportionately greater number of ecosystem services (see Millennium Ecosystem Assessment [MEA] 2005 for a discussion of provisioning, regulating, supporting, and cultural services) to human ...

Given currently high rates of extinction, it is critical to be able to predict how ecosystems will respond to loss of species and consequent changes in community structure. Much previous research in this area has been based on terrestrial systems, using synthetically assembled communities. There has been much less research on inter-trophic effects in different systems, using in situ removal experiments. Problems with the design of early experiments have made it difficult to determine whether reductions in ecosystem functioning in low diversity treatments were due to the number of species present or merely to the reduced likelihood of including particular (''key'') species or functional groups. We established a field experiment, using cage enclosures, to test whether the number or identity of grazing gastropods present would affect the diversity and productivity of intertidal algal communities. We found that there was no relationship between ecosystem functioning and diversity per se, but that different species had idiosyncratic effects. This appears to be a common feature of intertidal systems, which often contain strongly interacting species. In this case, the limpet Patella ulyssiponensis was the most influential primary consumer. Additional treatments enabled us to test the potential for other grazers to compensate for its loss. Early results (after four months) suggested that compensation was possible, implying potential redundancy of P. ulyssiponensis. This effect disappeared after 13 months, however, highlighting the context dependence of so-called redundancy and underlining the importance of long-term field-based experiments in this area.