Eco‐engineering urban infrastructure for marine and coastal biodiversity: Which interventions have the greatest ecological benefit?

Abstract

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

Mapping microhabitat thermal patterns in artificial breakwaters: Alteration of intertidal biodiversity by higher rock temperature

“…Choice of material with reduced potential to absorb/accumulate heat would be important during the design stage for construction of artificial structures. In addition, creation of small‐scale (cm) spatial heterogeneity in “top” or “sides” of rip‐raps with construction of grooves, pits, and/or small rock‐pools and transplant of mussels could complementarily increase thermal refuges availability for species settlement and or aggregations (Evans et al, ; Firth et al, ; Martins et al, ; Morris, Golding, Dafforn, & Coleman, ; Strain et al, ). In addition, “among rip‐raps” union, spaces or interstices would be modified through installing rock pools (Browne & Chapman, ; Waltham & Sheaves, ) to enhance water retaining features in a proportion of the breakwaters (e.g., ~10%) high enough to reduce overall structure heat gain.…”

“…These topographic features are microhabitats, which function as refuges to reduce thermal stress for both invertebrate and algal species (Garrity, ; Williams & Morritt, ) although rock pools can also become stressful environments in terms of temperature and salinity (Chan, ; Firth & Williams, ; Morritt et al, ). Thus, strategies to enhance the ecological value of artificial infrastructures in different latitudes are being made based on the provision of these refuges (Strain et al, ).…”

Patchiness in habitat distribution can enhance biological diversity of coastal engineering structures

“…Recently, efforts to enhance the diversity on coastal defence structures showed that structures such as seawalls and breakwaters could be modified in an attempt to increase the biodiversity they support. This has included the addition of simple topographic features such as pits, grooves, cracks or water‐retaining structures (Browne & Chapman, ; Chapman & Blockley, ; Coombes et al, ; Dafforn et al, ; Dafforn, Mayer‐Pinto, Morris, & Waltham, ; Evans et al, ; Firth, Browne, Knights, Hawkins, & Nash, ; Firth, Mieszkowska, et al, ; Firth, Schofield, White, Skov, & Hawkins, ; Firth, Thompson, et al, , ; Martins, Thompson, Neto, Hawkins, & Jenkins, ; Morris, Chapman, Firth, & Coleman, ; Morris et al, ; Strain et al, for a review). In order to further increase their ecological value, we need to understand how modifications made to coastal defence structures might affect species coexistence with potential long‐lasting effects (Martins, Jenkins, Neto, Hawkins, & Thompson, ).…”

“…In fact, most enhancements done to coastal defence structures (see earlier) are effective because they provide a refuge from environmental stressors or the risk of predation (Browne & Chapman, , ; Chapman & Blockley, ; Coombes et al, ; Evans et al, , ; Firth, Browne, et al, ; Firth, Knights, et al, ; Firth, Mieszkowska, et al, ; Firth, Schofield, et al, ; Firth, Thompson, et al, , ; Loke, Ladle, Bouma, & Todd, ; Martins et al, , ; reviews in Dafforn, Glasby, et al, ; Dafforn, Mayer‐Pinto, et al, ; Firth, Knights, et al, ; Strain et al, ). However, the magnitude of the effects varied among the functional groups and habitat settings considered (Strain et al, ). For instance, Martins et al () showed that the response of three intertidal snails to the addition of pits to a topographically simple seawall varied according to pit size and number: Littorinids ( Tectarius striatus and Melarhaphe neritoides ) tended to aggregate on small microhabitats, limpets ( Patella candei ) tended to aggregate in areas with large microhabitats, and all species tended to be more abundant with increasing microhabitat density.…”

Rock armour for birds and their prey: ecological enhancement of coastal engineering

“…Coombes et al, 2015;EA, 2008;Firth et al, 2014;Strain et al, 2017). These 'ecological enhancements' improve structural engineering through the selection of ecologically favourable materials and/or niche habitat designs, yet also satisfy engineering performance requirements.…”