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The diversity‐habitat complexity relationship has been utilised widely in conservation and biodiversity enhancement interventions, but few studies have attempted to tease apart the components of complexity that drive this relationship. The ecological engineering of seawalls is one area where this topic has advanced, albeit not often at scales relevant to fish.We constructed habitat enhancement units (Simple, Complex and Freestyle 'fish houses') out of hollow concrete blocks and installed them at the base of tropical rip‐rap seawalls. Simple and Complex fish houses were cuboid, had the same surface area and volume and included 100 holes (microhabitats). The holes in Simple fish houses were all the same size, whereas 25 size variations were used in the Complex design (volume‐independent manipulation of a single complexity element). The Freestyle fish house was non‐cuboid and had more overall volume, microhabitat types and sizes.We examined the volume‐independent (Simple vs. Complex fish houses) and volume‐dependent (Freestyle fish house) effects of microhabitat complexity on fish taxonomic and functional assemblage metrics at two spatial scales and across diel cycles. We also investigated diurnal and nocturnal fish‐microhabitat size relationships.There was a modest, but not significant, volume‐independent effect of complexity on fish assemblages. The Freestyle design, however, supported significantly greater abundance, species richness, and distinct taxonomic and functional compositions. These results were dependent on spatial scales and diel cycles. Diel variation in fish activity patterns resulted in stronger size‐matching relationships between fish and microhabitats at night than during the day.Synthesis and applications. Our study shows that, to enhance fish diversity, it is important to provide three‐dimensional habitat architecture that incorporates a wide range of microhabitat sizes and types. Our findings also highlight some key considerations when assessing the performance of intervention designs, including spatial‐scale dependent effects of structural complexity, diel variation in fish‐microhabitat relationships, and choice of intervention assessment metric (i.e. taxonomic vs. functional diversity). [ABSTRACT FROM AUTHOR]

There has been an increase in recognition of the benefits of employing nature-based coastal protection strategies to adapt to the impacts of climate change (e.g., increased storminess, sea-level rise). To enable broader use of nature-based methods, coastal managers and policymakers need to consider the placement and social acceptance of any methods considered. Most published spatial planning models for nature-based coastal protection currently do not utilise social data during site selection. We conducted a public survey of 452 respondents from Singapore, a highly urbanised coastal city-state, to assess Singaporean's perceptions of climate change impacts on coastal areas and their support of nature-based coastal protection. We also assessed the respondents willingness to accept trade-offs for the prioritisation of nature-based coastal protection and subsequently spatially mapped them. The results showed a high awareness of the potential impacts of climate change on coastal areas. Nature-based coastal protection was highly supported as the associated benefits, such as protection of wildlife and their habitats and climate change reduction, were aligned with public values of coastal areas. However, nature-based coastal protection may not be prioritised over human-made structures due to the perception that they are less effective, and respondents may not be willing to undergo 1) replacement of their favourite coastal area, 2) increased taxes, and 3) relocation, for their prioritisation. Through spatially mapping the relevant trade-offs, we found that only 11.1% of coastal areas had moderate or high likelihood of social barriers to nature-based coastal protection, highlighting their potential in Singapore. These findings underscore the importance of incorporating social factors in government land use planning decisions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)