Use environmentally-sensitive material on intertidal artificial structures
Overall effectiveness category Awaiting assessment
Number of studies: 8
Background information and definitions
Definition: ‘Environmentally-sensitive materials’ are materials that seek to maximize environmental benefits and/or minimize environmental risks of marine engineering.
Material type influences the settlement and survival of marine organisms in intertidal rocky habitats. Settlement preferences and competition lead to some species being more abundant than others on certain materials (Green et al. 2012; Iveša et al. 2010), but patterns vary by environmental conditions. Physical (lithology, hardness, porosity, colour, texture) and chemical (pH, mineralogy, toxicity) properties of rock and manufactured materials can affect how they weather over time and what communities develop on them (Coombes et al. 2011).
Marine artificial structures are often made from hard quarried rock, concrete, wood, steel or plastic, according to engineering requirements, cost and/or availability. Synthetic materials can be associated with the presence of non-native species (Dafforn 2017), whereas structures made from natural rock may support more natural rocky reef communities. There may be opportunities to use more environmentally-sensitive materials in structures or in eco-engineering habitat designs added to structures to enhance their biodiversity. Concrete is commonly-used in eco-engineering since it is durable and easy to mould into complex shapes. Yet adding manufactured concrete habitats to structures to enhance biodiversity may not deliver a net environmental gain because of the large CO2 footprint of concrete production (Heery et al. 2020). Concrete mixes can be manipulated to alter their physical and chemical properties (McManus et al. 2018; Natanzi et al. 2021) and environmental footprint (Dennis et al. 2018). Lower-footprint materials may be preferable, regardless of their effect on colonizing biodiversity; a neutral/no effect on biodiversity may still offer a higher net environmental gain (or lower net loss).
It is often not possible to separate the effects of the various physical and chemical properties of materials on biodiversity. Studies that directly examine the effects of creating different surface textures are included under the action “Create textured surfaces (≤1 mm) on intertidal artificial structures”; any other material comparisons are considered here. There are bodies of literature investigating the effects of material on settlement behaviour and ecological interactions in the laboratory and field (e.g. Anderson 1996; Iveša et al. 2010; Herbert & Hawkins 2006) and for anti-fouling applications (e.g. Hanson & Bell 1976). These studies are not included in this synopsis, which focusses on in situ conservation actions to promote colonization of biodiversity on marine artificial structures.
Anderson M.J. (1996) A chemical cue induces settlement of Sydney rock oysters, Saccostrea commercialis, in the laboratory and in the field. The Biological Bulletin, 190, 350–358.
Coombes M.A., Naylor L.A., Thompson R.C., Roast S.D., Gómez-Pujol L. & Fairhurst R.J. (2011) Colonization and weathering of engineering materials by marine microorganisms: an SEM study. Earth Surface Processes and Lanforms, 36, 585–593.
Dafforn K.A. (2017) Eco-engineering and management strategies for marine infrastructures to reduce establishment and dispersal of non-indigenous species. Management of Biological Invasions, 8, 153–161.
Dennis H.D., Evans A.J., Banner A.J. & Moore P.J. (2018) Reefcrete: reducing the environmental footprint of concretes for eco-engineering marine structures. Ecological Engineering, 120, 668–678.
Green D.S., Chapman M.G. & Blockley D.J. (2012) Ecological consequences of the type of rock used in the construction of artificial boulder-fields. Ecological Engineering, 46, 1–10.
Hanson C.H. & Bell J. (1976) Subtidal and intertidal marine fouling on artificial substrata in northern Puget Sound, Washington. Fishery Bulletin (United States), 74, 2.
Heery E.C., Lian K.Y., Loke L.H.L., Tan H.T.W. & Todd P.A. (2020) Evaluating seaweed farming as an eco-engineering strategy for 'blue' shoreline infrastructure. Ecological Engineering, 152, 105857.
Herbert R.J.H. & Hawkins S.J. (2006) Effect of rock type on the recruitment and early mortality of the barnacle Chthamalus montagui. Journal of Experimental Marine Biology and Ecology, 334, 96–108.
Iveša L., Chapman M.G., Underwood A.J. & Murphy R.J. (2010) Differential patterns of distribution of limpets on intertidal seawalls: experimental investigation of the roles of recruitment, survival and competition. Marine Ecology Progress Series, 407, 55–69.
McManus R.S., Archibald N., Comber S., Knights A.M., Thompson R.C. & Firth L.B. (2018) Partial replacement of cement for waste aggregates in concrete coastal and marine infrastructure: a foundation for ecological enhancement? Ecological Engineering, 120, 655–667.
Natanzi A.S., Thompson B.J., Brooks P.R., Crowe T.P. & McNally C. (2021) Influence of concrete properties on the initial biological colonisation of marine artificial structures. Ecological Engineering, 159, 106104.
Supporting evidence from individual studies
A replicated, randomized, controlled study in 2008–2009 on two intertidal rocky reefs on open coastlines in the Celtic Sea and the English Channel, UK (Coombes et al. 2011) found that limestone settlement plates supported lower microalgal abundance than concrete plates, while abundance on granite plates was higher than or similar to concrete depending on the type of microalgae. After eight months, round microalgal abundance was lower on limestone plates (5% cover) than concrete (61%), and higher than both on granite plates (82%). Filamentous microalgae was less abundant on limestone (13%) than granite (33%) and concrete (30%), which were similar. Settlement plates (100 × 100 mm) were made from limestone, granite and concrete. Two of each were randomly arranged horizontally in each of two patches at midshore on each of two rocky reefs in May 2008. Microalgal cover on plates was measured using a scanning electron microscope after eight months.Study and other actions tested
A replicated, randomized, controlled study in 2007–2008 in four intertidal boulder-fields in Sydney Harbour estuary, Australia (Green et al. 2012) found that using sandstone boulders in place of basalt boulders altered the macroalgae and non-mobile invertebrate community composition in two of four sites, and that abundances varied depending on the species group and site. After 10 months, macroalgae and non-mobile invertebrate community composition differed on sandstone and basalt boulders in two of four sites, but was similar in the other two sites (data reported as statistical model results). Sandstone boulders supported higher non-turf macroalgal abundance (0–17% cover) than basalt boulders (0–10%), and higher turf macroalgal abundance at one site (sandstone: 48%; basalt: 1%), but similar turf abundance at the other three sites (14–31 vs 9–25%). Sandstone boulders supported similar abundances of tubeworms (Serpulidae) and oysters (Ostreidae) to basalt boulders (tubeworms: 7–24 vs 8–27%; oysters: 0–9 vs 1–9%), but fewer barnacles (Cirripedia) (0 vs 1–2%). Five sandstone and five basalt oval quarried boulders (diameter: 350 mm) were randomly arranged at lowshore in each of two basalt (artificial) and two sandstone (unspecified) boulder-fields in June 2007. Macroalgae and non-mobile invertebrates were counted on boulders over 10 months.Study and other actions tested
A replicated, randomized, controlled study in 2014–2015 on an intertidal rocky reef on open coastline in the Irish Sea, UK (Dennis et al. 2018) found that hemp-concrete and shell-concrete settlement plates supported higher macroalgae and invertebrate cover than standard-concrete plates, and that hemp-concrete supported higher species richness than shell- and standard-concrete plates, with different community composition to standard-concrete plates. After 12 months, macroalgae and non-mobile invertebrate cover was similar on hemp-concrete (92% cover) and shell-concrete (74%) plates, and higher on both than standard-concrete plates (25%). Mobile invertebrate species richness was higher on hemp-concrete (8 species groups/plate) than shell-concrete (4/plate) and standard-concrete (3/plate), which were similar. Macroalgae and non-mobile invertebrate species richness was similar on all materials (hemp: 7/plate; shell: 6/plate; standard: 5/plate). Macroalgae and invertebrate community composition differed on hemp-concrete and standard-concrete, but shell-concrete was similar to both (data reported as statistical model results). Settlement plates (150 × 150 mm) were moulded from hemp-concrete, shell-concrete and standard-concrete. Five of each were randomly arranged horizontally at mid-lowshore on a rocky reef in October 2014. Macroalgae and invertebrates on plates were counted in the laboratory after 12 months.Study and other actions tested
A replicated, randomized, paired sites, controlled, before-and-after study in 2014–2016 on an intertidal seawall in a marina in the Mediterranean Sea, Israel (Perkol-Finkel et al. 2018) found that seawall panels made from ECOncreteTM, along with grooves, small ledges and holes created on them, supported higher macroalgae and invertebrate species diversity and richness and different community composition compared with standard-concrete seawall surfaces without added habitats. After 22 months, macroalgae and invertebrate species diversity (data reported as Shannon index) and richness was higher on ECOncreteTM panels with added habitats (8 species/quadrat) than on standard-concrete seawall surfaces without (3/quadrat), and compared with seawall surfaces before panels were attached (2/quadrat). Community composition differed between ECOncreteTM panels and standard-concrete surfaces (data reported as statistical model results). Five species groups (1 macroalgae, 4 non-mobile invertebrates) recorded on panels were absent from standard-concrete surfaces. It is not clear whether these effects were the direct result of using environmentally-sensitive material or creating grooves, ledges and/or holes. Seawall panels (height: 1.5 m; width: 0.9 m; thickness: 130 mm) were made from patented ECOncreteTM material using a formliner. Panels had multiple grooves, small ledges and holes. Four panels were attached to a vertical concrete seawall in November 2014. The top 0.3 m were intertidal. Panels were compared with standard-concrete seawall surfaces cleared of organisms (height: 0.3 m; width: 0.9 m) adjacent to each panel. Macroalgae and invertebrates were counted in one 300 × 300 mm randomly-placed quadrat on each panel and seawall surface during high tide over 22 months.Study and other actions tested
A replicated, randomized, paired sites, controlled study (year not reported) on an intertidal seawall in Ceuta Port in the Alboran Sea, Spain (Sempere-Valverde et al. 2018) found that sandstone settlement plates had higher chlorophyll-a and diatom abundance than limestone, slate, gabbro and concrete plates, and that material altered the diatom community composition but not their species richness or diversity. After two months, chlorophyll-a density was higher on sandstone settlement plates (18 μg/cm2) than limestone (3 μg/cm2), slate (3 μg/cm2) and concrete (6 μg/cm2) plates, which were all similar, while gabbro plates were similar to all materials (13 μg/cm2). Diatom species diversity and richness (data not reported) was similar on all materials, while their community composition differed (data reported as statistical model results), but it was not clear which materials differed. Total diatom abundance was higher on sandstone plates (841 individuals) than limestone (329), slate (104), gabbro (275) and concrete (173). Settlement plates (170 × 170 mm) were made from sandstone, limestone, slate, gabbro and concrete. One of each was randomly arranged horizontally on each of five midshore boulders along a limestone boulder seawall (month/year not reported). Plate surfaces had grooves and small protrusions created on them. Microalgae and chlorophyll-a on plates were measured using a scanning electron microscope and spectrophotometer, respectively, after two months.Study and other actions tested
A replicated, randomized, controlled study in 2016–2017 on three intertidal seawalls in the Clyde and Forth estuaries and on open coastline in the English Channel, UK (MacArthur et al. 2019) found that using limestone-cement in place of concrete in settlement plates, along with creating pits, grooves, small ridges and textured surfaces, had mixed effects on macroalgae and invertebrate species richness and invertebrate abundances on plates, depending on the site. After 18 months, in three of six comparisons, macroalgae and mobile invertebrate species richness was higher on limestone-cement settlement plates with added habitats (2 species/plate) than concrete plates without (1/plate). In four of six comparisons, the same was true for mobile invertebrate abundance (limestone-cement: 4–11; concrete: 1–2 individuals/plate) and barnacle (Cirripedia) cover (48–74 vs 22–34%). In the other comparisons, no significant effects were found for richness (3 comparisons: 1–2 vs 1/plate), mobile abundances (2 comparisons: 1–2 vs 2–3/plate) or barnacle cover (2 comparisons: 46–84 vs 22–83%). It is not clear whether these effects were the direct result of using environmentally-sensitive material or creating pits, grooves, ridges and/or texture. Settlement plates (150 × 150 mm) were moulded from limestone-cement or concrete. Limestone-cement plates had pits, grooves and ridges, or textured surfaces, while concrete plates did not. Eight plates of each limestone-cement design were randomly arranged at upper-midshore on each of two vertical concrete seawalls in April–May 2016. Eight concrete plates were attached on both walls plus one other. Macroalgae and invertebrates on plates were counted from photographs over 18 months.Study and other actions tested
A replicated, controlled study in 2018–2019 on four intertidal seawalls on island coastlines in the Singapore Strait, Singapore, and in the Plym and Tamar estuaries, UK (Hsiung et al. 2020) found that reducing the pH of concrete settlement plates did not alter the macroalgae and invertebrate community composition or increase their species richness or abundance on plates. Over 12 months, reduced-pH-concrete settlement plates supported 59 invertebrate species in total (Singapore: 46; UK: 13), while standard-concrete plates supported 57 (Singapore: 48; UK: 9) (data not statistically tested). Ten invertebrate species (8 mobile, 2 non-mobile) recorded on reduced-pH plates were absent from standard-concrete plates. After 12 months, macroalgae and invertebrate community composition (data reported as statistical model results) and species richness was similar on reduced-pH plates (3–21 species/plate) and standard-concrete plates (3–20/plate). The same was true for invertebrate abundance (6–187 vs 11–216 individuals/plate) and cover of limpets (Patellidae, Fissurellidae, Siphonariidae, Lottioidea) (both 1–5% cover), barnacles (Cirripedia) (18–24 vs 18–25%), ephemeral green macroalgae (4–5 vs 5–8%) and encrusting macroalgae (35 vs 29%). Concrete settlement plates (200 × 200 mm) were moulded with reduced pH (pH 7–10) and standard pH (pH 12–13). Twenty-four of each were attached at a 60° angle at midshore on each of two seawalls in both Singapore and the UK during February–March 2018. Plates had water-retaining pits created on them. Macroalgae on plates were counted from photographs and invertebrates in the laboratory over 12 months. Eight plates were missing and no longer provided habitat.Study and other actions tested
Referenced paperHsiung A.R., Tan W.T., Loke L.H.L., Firth L.B., Heery E.C., Ducker J., Clark V., Pek Y.S., Birch W.R., Ang A.C.F., Hartanto R.S., Chai T.M.F. & Todd P.A. (2020) Little evidence that lowering the pH of concrete supports greater biodiversity on tropical and temperate seawalls. Marine Ecology Progress Series, 656, 193-205.
A replicated, randomized, controlled study in 2018 on an intertidal breakwater on open coastline in the Irish Sea, Ireland (Natanzi et al. 2021) found that replacing standard Portland-cement with Ground Granulated Blast-Furnace Slag (GGBS), limestone-aggregate with granite-aggregate, and omitting plasticiser in concrete settlement plates had mixed effects on microalgal and barnacle (Cirripedia) abundances, depending on the material combination, wave-exposure and species group. After one month, on the wave-sheltered side of the breakwater, microalgal biomass was higher on plates with GGBS-cement (0.14–2.48 μg/cm2) than standard-cement (0.03–0.74 μg/cm2). Barnacle abundance varied depending on the aggregate and presence of plasticiser (GGBS-cement: 316–2,961 individuals/plate; standard-cement: 603–1,869/plate). There was no significant difference in microalgal or barnacle abundance between plates with granite-aggregate (microalgae: 0.03–1.66 μg/cm2; barnacles: 316–2,961/plate) and limestone-aggregate (microalgae: 0.06–2.48 μg/cm2; barnacles: 973–2,263/plate), or between plates without and with plasticiser (microalgae: 0.06–2.48 vs 0.03–1.66 μg/cm2; barnacles: 316–2,263 vs 603–2,961/plate). On the exposed side of the breakwater, results varied depending on the cement-aggregate-plasticiser combination and species group. Concrete settlement plates (200 × 200 mm) were moulded with different cement (GGBS, standard Portland-cement), aggregates (granite, limestone) and additives (no plasticiser, plasticiser). Six plates of each binder-aggregate-additive combination were randomly arranged vertically at mid-lowshore on the wave-sheltered side of a boulder breakwater in April 2018. Two plates of each were attached on the wave-exposed side. Microalgal biomass on plates was measured using a fluorometer and barnacles were counted from photographs after 1 month.Study and other actions tested