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

Habitat-forming species sustain biodiversity and ecosystem functioning in harsh environments through the amelioration of physical stress. Nonetheless, their role in shaping patterns of species distribution under future climate scenarios is generally overlooked. Focusing on coastal systems, we assess how habitat-forming species can influence the ability of stress-sensitive species to exhibit plastic responses, adapt to novel environmental conditions, or track suitable climates. Here, we argue that habitat-former populations could be managed as a nature-based solution against climate-driven loss of biodiversity. Drawing from different ecological and biological disciplines, we identify a series of actions to sustain the resilience of marine habitat-forming species to climate change, as well as their effectiveness and reliability in rescuing stress-sensitive species from increasingly adverse environmental conditions.

The intertidal microgastropods Eatoniella atropurpurea, Amphithalamus incidata and Eatonina rubrilabiata are principally found at mid- to low-shore levels in coralline turf and in patches of sediment close to algal turf on rocky shores. All three species are more abundant in coralline turf (i.e. algal beds composed primarily of Corallina officinalis Linnaeus, often containing patches of sediment) than in sediment, although the latter two are also quite abundant in patches of sediment. Eatoniella atropurpurea seem to live on branches of coralline algae, whereas Eatonina rubrilabiata and A. incidata seem to inhabit the sediment. In this study, we investigated whether or not behaviour of these animals accounts for the patterns observed in the field. Particularly, this study deals with choices amongst three microhabitats (coralline algae, coralline algae plus sediment and sediment) by these three species of microgastropods. Laboratory experiments were designed to examine preferences. The designs of such experiments are complex because demonstrating preference necessitates demonstrating different behaviour when confronted with choices from that showed when no choice is available. This study describes an appropriate series of hypotheses about preferences and experimental designs to test them. Preferences were indicated by differences in occupancy of the microhabitats when presented with a mixture and when each type is presented alone. In such experiments, snails did show preferences, except for A. incidata which did not show a pattern. Thus, the behaviour could, at least partially, account for the patterns of distribution in the field. The designs of experiments used here may be of value in other studies of preferences among habitats.

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