The world’s coastal zones are experiencing rapid development and an increase in storms and flooding. These hazards put coastal communities at heightened risk, which may increase with habitat loss. Here we analyse globally the role and cost effectiveness of coral reefs in risk reduction. Meta-analyses reveal that coral reefs provide substantial protection against natural hazards by reducing wave energy by an average of 97%. Reef crests alone dissipate most of this energy (86%). There are 100 million or more people who may receive risk reduction benefits from reefs or bear hazard mitigation and adaptation costs if reefs are degraded. We show that coral reefs can provide comparable wave attenuation benefits to artificial defences such as breakwaters, and reef defences can be enhanced cost effectively. Reefs face growing threats yet there is opportunity to guide adaptation and hazard mitigation investments towards reef restoration to strengthen this first line of coastal defence.

Firth, L. B., Thompson, R. C., Bohn, K., Abbiati, M., Airoldi, L., Bouma, T. J., Bozzeda, F., Ceccherelli, V. U., Colangelo, M. A., Evans, A., Ferrario, F., Hanely, M. E., Hinz, H., Hoggart, S. P. G., Jackson, J. E., Moore, P., Morgan, E. H., Perkol-Finkel, S., Skov, M. W., Strain, E. M., van Belzen, J., Hawkins, S. J. (2014). Between a rock and a hard place: Environmental and engineering considerations when designing coastal defence structures. Coastal Engineering, 87, 122-135Coastal defence structures are proliferating as a result of rising sea levels and stormier seas. With the realisation that most coastal infrastructure cannot be lost or removed, research is required into ways that coastal defence structures can be built to meet engineering requirements, whilst also providing relevant ecosystem services so-called ecological engineering. This approach requires an understanding of the types of assemblages and their functional roles that are desirable and feasible in these novel ecosystems. We review the major impacts coastal defence structures have on surrounding environments and recent experiments informing building coastal defences in a more ecologically sustainable manner. We summarise research carried out during the THESEUS project (2009-2014) which optimised the design of coastal defence structures with the aim to conserve or restore native species diversity. Native biodiversity could be manipulated on defence structures through various interventions: we created artificial rock pools, pits and crevices on breakwaters; we deployed a precast habitat enhancement unit in a coastal defence scheme; we tested the use of a mixture of stone sizes in gabion baskets; and we gardened native habitat-forming species, such as threatened canopy-forming algae on coastal defence structures. Finally, we outline guidelines and recommendations to provide multiple ecosystem services while maintaining engineering efficacy. This work demonstrated that simple enhancement methods can be cost-effective measures to manage local biodiversity. Care is required, however, in the wholesale implementation of these recommendations without full consideration of the desired effects and overall management goals. (C) 2013 Elsevier B.V. All rights reserved.authorsversionPeer reviewe

1. With nearly two-thirds of the human population concentrated along coastlines, coastal development and urbanized seascapes are inevitable. Proliferation of coastal and marine infrastructures, such as breakwaters, ports, seawalls and offshore installations, is associated with loss of natural habitats. This calls for new strategies aimed at elevating the ecological and biological value of coastal infrastructures, while minimizing their ecological footprint. 2. We explored the feasibility of using coastal defence structures as a scaffold for the conservation of threatened marine species. We experimented with fucoids, canopy-forming algae on Mediterranean coasts, in the light of their declared conservation priority. We transplanted juveniles of Cystoseira barbata to a number of breakwaters and natural sites along the Adriatic Sea (Italy) and tested which factors could facilitate or inhibit its successful establishment. 3. Survival of transplanted C. barbata was greater at most artificial and natural sites examined compared to the native sites where severe habitat loss was ongoing. Survival was greater at landward compared to seaward positions on the infrastructure, while no relevant effects of substratum characteristics (horizontal vs. vertical orientation, variable composition and increasing complexity) were observed. Lack of surrounding adult fronds did not impair the survival or growth of the transplants, suggesting a high transplantation potential also on novel infrastructures. 4. Success of transplantation in areas remote from the source population was limited by bio-tic disturbance, which was more intense on coastal infrastructures in sedimentary environments compared to natural rocky sites. 5. Synthesis and applications. Coastal and marine infrastructures can be harnessed to enhance desired species (such as threatened canopy-forming algae). A comprehensive understanding of the ecological functioning of these urban seascapes compared to natural habitats is required to minimize detrimental impacts, or potentially increase the ecological value, of coastal structures and efficiently incorporate such strategies into management and conservation actions. We investigated the influence of habitat type (including natural and artificial), surface complexity , herbivore exclusion, proximity to established populations and orientation on the transplantation success of threatened algae.

Summary Artificial structures are sprawling in marine seascapes as a result of burgeoning coastal populations, increasing development and energy demand, and greater risks from climate change, storm surges and sea level rise. Interest in designing marine developments that maintain vital ecosystems and critical services is growing, but progress requires understanding the factors that influence the ecological performance of these novel artificial habitats. We combined field observations and experiments along 500 km of the North Adriatic coastline to analyse the performance of artificial substrata as habitats to support canopy‐forming algae belonging to the genus Cystoseira, among the most ecologically relevant foundation species along rocky Mediterranean coastlines. We aimed to: clarify the underlying factors controlling the growth of Cystoseira in the artificial habitat; contrast the relative importance of these factors between artificial and natural habitats; and test the generality of the results across different sites and species of Cystoseira. We found that: (i) the growth of canopy algae was significantly lower on artificial structures compared to rocky reefs; (ii) such lower growth of canopy algae was not related to less favourable abiotic conditions but to higher biotic disturbance from both consumptive and nonconsumptive interactions on the artificial structures compared to the natural reef; and iii) this was consistent across different study sites and canopy‐forming species. We conclude that biological factors influencing the growth of canopy algae, such as herbivory or other nonconsumptive disturbances, can differ substantially between artificial and natural habitats. The unusually large and previously unreported biotic pressure characterizing many artificial structures can negatively affect their performance as habitats to support ecologically relevant, foundation species. Synthesis and applications. While nearly all considerations to improve the ecological performance of hard marine infrastructures focus on abiotic factors (e.g. construction materials, surface texture, habitat complexity or water quality), careful consideration of critical biotic factors is also needed to further progress the green engineering of sprawling marine infrastructures.