Use environmentally-sensitive material on subtidal artificial structures

Overall effectiveness category Awaiting assessment
Number of studies: 14
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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 subtidal rocky habitats. Settlement preferences and competition lead to some species being more abundant than others on certain materials (Andersson et al. 2009; Guidetti et al. 2004), 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 designs 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 subtidal 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. Davis et al. 2017; Glasby 2000), for artificial reefs and coral gardening (reviewed by Baine 2001; Spieler et al. 2001), and for anti-fouling applications (e.g. Hanson & Bell 1976). Unless the relevance is explicitly highlighted by the authors, these studies are not included in this synopsis, which focusses on in situ conservation actions to promote colonization of biodiversity on marine artificial structures that are engineered to fulfil a primary function other than providing artificial habitats.

^{Andersson M.H., Berggren M., Wilhelmsson D. & Öhman M.C. (2009) Epibenthic colonization of concrete and steel pilings in a cold-temperate embayment: a field experiment. Helgoland Marine Research, 63, 249–260.}

^{Baine M. (2001) Artificial reefs: a review of their design, application, management and performance. Ocean & Coastal Management, 44, 241–259.}

^{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.}

^{Davis K.L., Coleman M.A., Connell S.D., Russell B.D., Gillanders B.M. & Kelaher B.P. (2017) Ecological performance of construction materials subject to ocean climate change. Marine Environmental Research, 131, 177–182.}

^{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.}

^{Glasby T.M. (2000) Surface composition and orientation interact to affect subtidal epibiota. Journal of Experimental Marine Biology and Ecology, 248, 177–190.}

^{Guidetti P., Bianchi C.N., Chiantore M., Schiaparelli S., Morri C. & Cattaneo-Vietti R. (2004) Living on the rocks: substrate mineralogy and the structure of subtidal rocky substrate communities in the Mediterranean Sea. Marine Ecology Progress Series, 274, 57–68.}

^{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.}

^{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.}

^{Spieler R.E., Gilliam D.S. & Sherman R.L. (2001) Artificial substrate and coral reef restoration: what do we need to know to know what we need. Bulletin of Marine Science, 69, 1013–1030.}

Study locations

Key messages

Fourteen studies examined the effects of using environmentally-sensitive material on subtidal artificial structures on the biodiversity of those structures. Seven studies were on open coastlines in the United Arab Emirates, Italy, Israel, southeast Spain, and in France, the UK, Portugal and Spain. Three were in marinas in northern Israel and the UK, two were in estuaries in southeast Australia and eastern USA, one was in a lagoon in Mayotte, and one was in a port in Germany.

COMMUNITY RESPONSE (11 STUDIES)

Overall community composition (11 studies): Six of 11 replicated, controlled studies (including eight randomized, three paired sites and one before-and-after study) in Australia, the United Arab Emirates, Italy, Israel, the USA, the UK, Spain and Germany found that using shell-concrete or quarried rock in place of standard-concrete on subtidal artificial structures, or using ECOncrete^TM in place of standard-concrete or fibreglass, along with creating texture, grooves, holes, pits and/or small ledges, altered the combined macroalgae and invertebrate community composition on structure surfaces. Three studies found that using quarried rock or blast-furnace-cement-concrete in place of standard-concrete did not alter the community composition, while one found mixed effects depending on the type of rock tested and the site. One found that using different cement mixes in concrete (including some with recycled cements) altered the community composition of native species, but not non-natives. Three of the studies also reported that ECOncrete^TM surfaces with added habitats supported mobile invertebrate, non-mobile invertebrate and/or fish species that were absent from standard-concrete or fibreglass structure surfaces.
Overall richness/diversity (7 studies): Three of seven replicated, controlled studies (including five randomized, two paired sites and one before-and-after study) in Italy, Israel, the USA, the UK and Spain found that using quarried rock, shell-concrete or recycled-cement-concrete in place of standard-concrete on subtidal artificial structures had mixed effects on the combined macroalgae and invertebrate species richness on structure surfaces, depending on the site, surface orientation or type of cement tested. One of the studies, along with one other, found that using shell-concrete or quarried rock did not increase the species diversity and/or richness, while one found that using recycled cement did not increase the non-native species richness. Three studies found that using ECOncrete^TM, along with creating texture, grooves, holes, pits and/or small ledges, did increase the species diversity and/or richness on and around structures.
Algal richness/diversity (1 study): One replicated, randomized, controlled study in the UK found that using recycled-cement-concrete in place of standard-concrete on subtidal artificial structures did not increase the diatom species richness on structure surfaces.

POPULATION RESPONSE (11 STUDIES)

Overall abundance (7 studies): Three of seven replicated studies (including six controlled, four randomized and one paired sites study) in the United Arab Emirates, Italy, Israel, the USA, the UK, Spain, and in France, the UK, Portugal and Spain found that using quarried rock or shell-concrete in place of standard-concrete on subtidal artificial structures did not increase the combined macroalgae and invertebrate abundance on structure surfaces. Two studies found mixed effects, depending on the type of quarried rock or concrete tested and/or the location. One found that using ECOncrete^TM in place of fibreglass, along with creating textured surfaces, increased the live cover and biomass, while one found that different ECOncrete^TM and standard-concrete mixes supported different cover and inorganic biomass but similar organic biomass.
Algal abundance (6 studies): Four of six replicated, controlled studies (including four randomized and one paired sites study) in Australia, the United Arab Emirates, Italy, Israel and the UK found that using quarried rock or recycled-cement-concrete in place of standard-concrete on subtidal artificial structures did not increase the abundance of brown, turf or coralline macroalgae, canopy macroalgae recruits or diatoms on structure surfaces. Two studies found that using quarried rock or using ECOncrete^TM, along with creating grooves, holes and pits, had mixed effects on macroalgal abundance, depending on the species group and/or site. One of the studies found that using quarried rock increased red and green macroalgal abundance.
Invertebrate abundance (6 studies): Three of six replicated, controlled studies (including four randomized and one paired sites study) in Austalia, the United Arab Emirates, Italy, Israel and the UK found that using quarried rock in place of concrete on subtidal artificial structures, or using ECOncrete^TM, along with creating grooves, holes and pits, had mixed effects on the abundance of non-mobile invertebrates, mobile invertebrates or coral recruits on structure surfaces, depending on the type of rock tested, the species group and/or the site. One of the studies, along with one other, found that using quarried rock did not increase the abundance of sponges, bryozoans, ascidians, mussels, barnacles, or Serpulid tubeworms, but in one it decreased Spirorbid tubeworm abundance. One study found that using shell-concrete increased bivalve abundance. One found that different ECOncrete^TM and standard-concrete mixes supported different coral abundance.
Fish abundance (1 study): One replicated, controlled study in Israel found that using ECOncrete^TM in place of standard-concrete on subtidal artificial structures, along with creating grooves, holes and pits, had mixed effects on fish abundances, depending on the species group.

BEHAVIOUR (1 STUDY)

Use (1 study): One study in Mayotte reported that basalt rock surfaces created on a concrete subtidal artificial structure, along with small and large swimthroughs, were used by juvenile spiny lobsters and groupers, sea firs, and adult fishes from five families.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A replicated, randomized, paired sites, controlled study in 1998–1999 on four subtidal pontoons and four rocky reefs in Sydney Harbour estuary, Australia (Connell 2000) found that sandstone and concrete settlement plates supported similar macroalgae and invertebrate community composition, while abundances varied depending on the species group. After seven months, macroalgae and non-mobile invertebrate community composition was similar on sandstone and concrete settlement plates (data reported as statistical model results). Sandstone plates supported higher abundance of red macroalgae (2–33% cover) and green macroalgae (2–13%) than concrete plates (red: 1–15%; green: 1–7%), but fewer Spirorbid tubeworms (0–37 vs 0–48%). Abundances were similar on sandstone and concrete plates for brown macroalgae (1–10 vs 1–17%), mussels (Mytilus edulis: 1–34 vs 3–44%), barnacles (Cirripedia: 1–37 vs 1–41%), sponges (Porifera: both 1–9%), bryozoans (Bryozoa: 0–38 vs 0–49%), ascidians (Ascidiacea: 0–25 vs 0–16%) and Serpulid tubeworms (3–17 vs 3–16%). Settlement plates (150 × 150 mm) were made from sandstone and concrete. Five of each were randomly arranged vertically at 0.3 m depth on each of four concrete pontoons and at 1.5 m depth on each of four adjacent sandstone reefs in June 1998. Macroalgae and non-mobile invertebrates on plates were counted in the laboratory after seven months.
Study and other actions tested
Referenced paper
Connell S.D. (2000) Floating pontoons create novel habitats for subtidal epibiota. Journal of Experimental Marine Biology and Ecology, 247, 183-194.
A replicated, randomized, controlled study in 2007–2008 on two subtidal breakwaters and two rocky reefs on open coastline in the Persian Gulf, United Arab Emirates (Burt et al. 2009) found that sandstone, terracotta, granite, gabbro and concrete settlement plates supported similar macroalgae and invertebrate community composition and abundances, while juvenile coral (Scleractinia, Alcyonacea) abundances varied depending on the site. After 12 months, macroalgae and non-mobile invertebrate cover was similar on sandstone (65%), terracotta (75%), granite (85%), gabbro (80%) and concrete (79%) settlement plates. The same was true for abundances of macroalgal turf, coralline algae (Corallinales), sponges (Porifera), bryozoans (Bryozoa) and ascidians (Ascidiacea) (data not reported) and the community composition (data reported as statistical model results). At one of four sites, juvenile corals were more abundant on gabbro (7 colonies/plate) than sandstone (3/plate) and concrete (3/plate) plates, while no other significant differences were found (terracotta: 7/plate; granite: 5/plate). At the other sites, few corals were recorded with no significant differences between materials (all 0/plate). Settlement plates (100 × 100 mm) were made from sandstone, terracotta, granite, gabbro and concrete. Twenty-five of each were randomly arranged horizontally 10–15 mm above the substrate at 4 m depth on each of two breakwaters and two rocky reefs in April 2007. Macroalgae and non-mobile invertebrates on the undersides of plates were counted from photographs and juvenile corals in the laboratory after 12 months. Twenty-five plates were missing and no longer provided habitat.
Study and other actions tested
Referenced paper
Burt J., Bartholomew A., Bauman A., Saif A. & Sale P.F. (2009) Coral recruitment and early benthic community development on several materials used in the construction of artificial reefs and breakwaters. Journal of Experimental Marine Biology and Ecology, 373, 72-78.
A replicated, randomized, controlled study in 2005 on three subtidal rocky reefs on open coastlines in the Adriatic Sea and the Ionian Sea, Italy (Guarnieri et al. 2009) found that limestone, sandstone, granite and concrete settlement plates supported similar macroalgae and non-mobile invertebrate live cover, while community composition, species richness and abundances varied depending on the site and species group. After nine months, macroalgae and non-mobile invertebrate community composition differed between limestone and concrete and between sandstone and concrete plates in four of six sites each, and between sandstone and concrete plates in two of six sites, but did not differ in the other sites (data reported as statistical model results). Live cover was similar on all materials, while species richness comparisons varied by site (data not reported). Abundance comparisons varied by species group and site (see paper for results). Limestone, sandstone, granite and concrete settlement plates (150 × 100 mm) were made with and without textured surfaces. Five of each material-texture combination were randomly arranged horizontally at 5 m depth in each of two sites on each of three limestone reefs in February 2005. Macroalgae and non-mobile invertebrates on plates were counted in the laboratory after nine months.
Study and other actions tested
Referenced paper
Guarnieri G., Terlizzi A., Bevilacqua S. & Fraschetti S. (2009) Local vs regional effects of substratum on early colonization stages of sessile assemblages. Biofouling, 25, 593-604.
A study in 2009–2010 on a subtidal pipeline in a lagoon in the Mozambique Channel, Mayotte (Pioch et al. 2011) reported that pipeline anchor-weights with basalt rock surfaces created on them, along with small and large swimthroughs, were used by juvenile spiny lobsters Panulirus versicolor, juvenile blue-and-yellow groupers Epinephelus flavocaeruleus, sea firs (Hydrozoa), and adult fishes from five families. After one month, juvenile spiny lobsters and blue-and-yellow groupers, sea firs, and adult damselfish/clownfish (Pomacentridae), wrasse (Labridae), butterflyfish (Chaetodontidae), squirrelfish/soldierfish (Holocentridae) and surgeonfish (Acanthuridae) were recorded on and around anchor-weights with basalt rocks and swimthrough habitats. Basalt rocks (dimensions/numbers not reported) were attached over horizontal surfaces of concrete anchor-weights placed over a seabed pipeline (400 mm diameter). Small and large swimthrough habitats were also created on the anchor-weights. A total of 260 anchor-weights were placed with one every 10 m along the pipeline at 0–26 m depth during December 2009–March 2010. Fishes were counted on and around the pipeline from videos after 1 month.
Study and other actions tested
Referenced paper
Pioch S., Saussola P., Kilfoyle K. & Spieler R. (2011) Ecological design of marine construction for socio-economic benefits: ecosystem integration of a pipeline in coral reef area. Procedia Environmental Sciences, 9, 148-152.
A replicated, randomized, controlled study in 2009 on a subtidal rocky reef on open coastline in the Adriatic Sea, Italy (Perkol-Finkel et al. 2012) found that limestone, clay and concrete settlement plates supported similar numbers of juvenile canopy algae Cystoseira barbata. After three months, there was no significant difference in the average number of canopy algae recruits on limestone (25/plate), clay (29/plate) and concrete (12/plate) settlement plates. Six settlement plates (100 × 100 mm) of each of three materials (limestone, clay, concrete) were randomly arranged horizontally on a rocky reef at 3 m depth in March 2009. Recruits of juvenile canopy algae settled onto plates were counted after three months.
Study and other actions tested
Referenced paper
Perkol-Finkel S., Ferrario F., Nicotera V. & Airoldi L. (2012) Conservation challenges in urban seascapes: promoting the growth of threatened species on coastal infrastructures. Journal of Applied Ecology, 49, 1457-1466.
A replicated, randomized, controlled study (year not reported) on open coastlines in the Mediterranean Sea and the Gulf of Aqaba, Israel (Perkol-Finkel et al. 2014) found that settlement plates made from different concrete mixes (including five ECOncrete^TM and one standard-concrete mix) supported different macroalgae and non-mobile invertebrate community composition, coral (Scleractinia, Alcyonacea) abundance and inorganic biomass, but similar organic biomass. Over 12 months, macroalgae and non-mobile invertebrate community composition differed on different concrete mixes (including five ECOncrete^TM and one standard-concrete mix), but it was not clear which materials differed in which locations (data reported as statistical model results). The same was true for their abundance (ECOncrete^TM: 81–100% cover; standard-concrete: 80–92%), inorganic biomass (ECOncrete^TM: 153–659 g/m²; standard-concrete: 168–332 g/m²) and coral abundance (2–16 vs 3–5 recruits in total). Organic biomass was similar on ECOncrete^TM (16–73 g/m²) and standard-concrete (30–79 g/m²). Settlement plates (150 × 150 mm) were moulded from six concrete mixes. Five were patented ECOncrete^TM mixes with reduced pH (pH 9–11), reduced Portland-cement and alternative cements and additives (details not reported) while one was standard-concrete (pH 13–14, Portland cement). Plates had textured surfaces on one side and were flat on the other. Ten of each material were randomly arranged horizontally with textured surfaces facing upwards on frames at 6 m depth in the Mediterranean Sea and at 10 m in the Gulf of Aqaba (month/year not reported). Macroalgae and invertebrates on plates were counted and biomass (dry weight) was recorded in the laboratory over 12 months.
Study and other actions tested
Referenced paper
Perkol-Finkel S. & Sella I. (2014) Ecologically-active concrete for coastal and marine infrastructure: innovative matrices and designs. Pages 1139-1149 in: W. Allsop & K. Burgess (eds.) From Sea to Shore – Meeting the Challenges of the Sea: (Coasts, Marine Structures and Breakwaters 2013). ICE Publishing, London.
A replicated, controlled study in 2012–2014 on two subtidal breakwaters on open coastline in the Mediterranean Sea, Israel (Sella & Perkol-Finkel 2015) found that breakwater blocks made from ECOncrete^TM, along with pits, grooves and holes created on them, supported different macroalgae and invertebrate community composition with higher species diversity than standard-concrete blocks without added habitats, while macroalgae, invertebrate and fish abundances varied depending on the species group. After 24 months, the macroalgae and invertebrate species diversity was higher on ECOncrete^TM blocks with added habitats than standard-concrete blocks without (data reported as Shannon index) and the community composition differed (data reported as statistical model results). Thirty species (7 mobile invertebrates, 14 non-mobile invertebrates, 9 fishes) recorded on and around ECOncrete^TM blocks were absent from standard blocks. Species abundances varied on materials depending on the species group (see paper for results). It is not clear whether these effects were the direct result of using environmentally-sensitive material or creating grooves, pits and/or holes. Breakwater blocks (1 × 1 × 1 m) were made from three patented ECOncrete^TM materials (lower pH and different cement/additives to standard concrete) using a formliner. Five of each were placed at 5–7 m depth on a concrete-block breakwater during construction in July 2012. Blocks had multiple grooves, pits and holes. Five standard-concrete blocks (1.7 × 1.7 × 1.7 m) without added habitats were placed on a similar breakwater 80 m away. Macroalgae and invertebrates on blocks, and fishes on and around blocks, were counted over 24 months.
Study and other actions tested
Referenced paper
Sella I. & Perkol-Finkel S. (2015) Blue is the new green – ecological enhancement of concrete based coastal and marine infrastructure. Ecological Engineering, 84, 260-272.
A replicated, controlled study in 2013–2014 on 24 jetty pilings in the Hudson River estuary, USA (Perkol-Finkel & Sella 2016) found that using ECOncrete^TM on pilings, along with creating textured surfaces, increased the macroalgae and invertebrate species richness, cover and biomass and altered the community composition on piling surfaces. After 14 months, ECOncrete^TM pilings with textured surfaces supported 18 macroalgae and invertebrate species with 90–100% cover, while fibreglass pilings without texture supported nine species with 40–85% cover (data not statistically tested). Biomass was higher on ECOncrete^TM pilings (0.07 g/cm²) than fibreglass pilings (0.02 g/cm²) and the community composition differed (data reported as statistical model results). Over 14 months, six species (4 non-mobile invertebrates, 2 mobile invertebrates) recorded on ECOncrete^TM pilings were absent from fibreglass ones. It is not clear whether these effects were the direct result of using environmentally-sensitive material or creating textured surfaces. Jetty piling encasements were made from patented ECOncrete^TM material using a formliner during maintenance works. Nine ECOncrete^TM encasements with textured surfaces and three untextured fibreglass encasements were attached around pilings in each of two sites on a jetty in June 2013 (depth not reported). Macroalgae and invertebrates were counted on and around pilings and biomass was measured (dry weight) in the laboratory over 14 months.
Study and other actions tested
Referenced paper
Perkol-Finkel S. & Sella I. (2016) Blue is the new green – harnessing urban coastal infrastructure for ecological enhancement. Pages 139-149 in: A. Baptiste (ed.) Coastal Management: Changing Coast, Changing Climate, Changing Minds. ICE Publishing, London.
A replicated, randomized, paired sites, controlled, before-and-after study in 2014–2016 on a subtidal seawall in a marina in the Mediterranean Sea, Israel (Perkol-Finkel et al. 2018) found that seawall panels made from ECOncrete^TM, 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 ECOncrete^TM panels with added habitats (9 species/quadrat) than on standard-concrete seawall surfaces without (5/quadrat), and compared with seawall surfaces before panels were attached (1/quadrat). Community composition differed between ECOncrete^TM panels and standard-concrete surfaces (data reported as statistical model results). Two non-mobile invertebrate species groups 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 ECOncrete^TM 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 bottom 1.2 m were subtidal. Panels were compared with standard-concrete seawall surfaces cleared of organisms (height: 1.2 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
Referenced paper
Perkol-Finkel S., Hadary T., Rella A., Shirazi R. & Sella I. (2018) Seascape architecture – incorporating ecological considerations in design of coastal and marine infrastructure. Ecological Engineering, 120, 645-654.
A replicated, randomized, controlled study in 2016 in a marina in the Fal estuary, UK (Hanlon et al. 2018) found that shell-concrete settlement plates supported different macroalgae and invertebrate community composition, with higher bivalve abundance but similar species diversity and live cover to standard-concrete plates, while species richness varied depending on the surface orientation. After six months, shell-concrete settlement plates supported different macroalgae and invertebrate community composition (data reported as statistical model results) with similar species diversity and live cover (data not reported) to standard-concrete plates. Species richness comparisons varied depending on the surface orientation (data not reported). Bivalve abundance (Anomia ephippium, Hiatella arctica, Musculus costulatas) was 38% higher on shell-concrete than standard-concrete plates. Settlement plates (150 × 150 mm) were moulded from oyster-shell-concrete and standard-concrete. Plates had grooves and small protrusions on one surface, but were flat on the other. Forty plates were suspended horizontally, randomly arranged, beneath floating pontoons at 2–3 m depth in April 2016. Ten of each material had grooves/protrusions facing up, while 10 of each faced down. Macroalgae and invertebrates on upward- and downward-facing surfaces were counted in the laboratory over six months.
Study and other actions tested
Referenced paper
Hanlon N., Firth L.B. & Knights A.M. (2018) Time-dependent effects of orientation, heterogeneity and composition determines benthic biological community recruitment patterns on subtidal artificial structures. Ecological Engineering, 112, 219-228.
A replicated, randomized, controlled study in 2016 in a marina in the Plym estuary, UK (McManus et al. 2018) found that replacing standard Portland-cement with Ground Granulated Blast-Furnace Slag (GGBS), Pulverized Fly Ash (PFA), or a mix of both, in concrete settlement plates did not affect the diatom species richness or abundance on plates, or the non-native macroalgae and non-mobile invertebrate species richness or community composition, but had mixed effects on the native species richness and community composition, depending on the cement used. Over four weeks, diatom species richness and live cover was similar on GGBS-concrete (2 species/plate; 19% cover), PFA-concrete (2/plate; 12%), mixed-concrete (2/plate; 20%) and standard-concrete (2/plate; 12%) settlement plates. After seven weeks, native macroalgae and non-mobile invertebrate community composition differed on different materials (data reported as statistical model results), but it was not clear which materials differed. Native species richness was similar on PFA-concrete (8 species/plate) and standard-concrete (9/plate), but lower on GGBS-concrete (8/plate) and mixed-concrete (7/plate) than standard-concrete. Non-native community composition and species richness was similar on all materials (1–2 species/plate). Settlement plates (20 × 20 mm) were moulded with recycled cement (GGBS, PFA, or a mix of both) or standard Portland-cement. Eighty of each were suspended vertically, randomly arranged, beneath floating pontoons at 0.5 m depth in June 2016. Diatoms on plates were counted using a scanning electron microscope over four weeks, and macroalgae and invertebrates in the laboratory after seven weeks.
Study and other actions tested
Referenced paper
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.
A replicated, randomized, paired sites, controlled study in 2014–2015 on a subtidal rocky reef on open coastline in the Alboran Sea, Spain (Sempere-Valverde et al. 2018) found that sandstone, limestone, slate and gabbro settlement plates supported similar macroalgae and non-mobile invertebrate species diversity and richness but different community composition to concrete plates, and that live cover was higher on sandstone than concrete plates. Over 11 months, macroalgae and non-mobile invertebrate species diversity was similar on sandstone, limestone, slate, gabbro and concrete settlement plates (data reported as Shannon index). Community composition differed on all materials, apart from sandstone vs gabbro and slate vs gabbro (data reported as statistical model results), and sandstone plates were more similar to natural rock surfaces than the other materials were (data not statistically tested). Total live cover was higher on sandstone than concrete and gabbro plates, while species richness was higher on sandstone than limestone (data not reported), but no other significant differences were found. Settlement plates (170 × 170 mm) were made from sandstone, limestone, slate, gabbro or concrete. Two of each material were randomly arranged horizontally at 15 m depth in each of three sites on a gneiss reef in June 2014. Plate surfaces had grooves and small protrusions. Macroalgae and non-mobile invertebrates on each pair of plates and on adjacent natural rock surfaces (170 × 170 mm) were counted from photographs over 11 months.
Study and other actions tested
Referenced paper
Sempere-Valverde J., Ostalé-Valriberas E., Farfán G.M. & Espinosa F. (2018) Substratum type affects recruitment and development of marine assemblages over artificial substrata: a case study in the Alboran Sea. Estuarine, Coastal and Shelf Science, 204, 56-65.
A replicated, randomized, controlled study in 2017–2018 in Jade Weser Port in the North Sea, Germany (Becker et al. 2021) found that using blast-furnace-cement in place of standard Portland-cement and varying the aggregates in concrete settlement blocks did not alter the community composition of macroalgae, microalgae and non-mobile invertebrates on blocks. After 12 months, the community composition of macroalgae, microalgae and non-mobile invertebrates was similar on blast-furnace-cement concrete and standard-concrete blocks regardless of their aggregate composition (data reported as statistical model results). Concrete settlement blocks (150 × 150 × 150 mm) were moulded with blast-furnace cement or standard Portland-cement. There were four blast-furnace-cement concretes with varying aggregate mixes (sand, gravel, metallic slags; see paper for details) and one standard-concrete mix with sand and gravel aggregate. Three blocks of each blast-furnace-cement mix and three standard-concrete blocks were randomly arranged on frames suspended beneath floating pontoons at 1.5 m depth in April 2017. Macroalgae, microalgae and non-mobile invertebrates on top horizontal and both vertical block surfaces were counted in the laboratory after 12 months.
Study and other actions tested
Referenced paper
Becker L.R., Kröncke I., Ehrenberg A., Feldrappe V. & Bischof K. (2021) Benthic community establishment on different concrete mixtures introduced to a German deep-water port. Helgoland Marine Research, 75, 1-12.
A replicated study (year not reported) on open coastlines in the English Channel, France and the UK, Matosinhos Bay, Portugal, and Santander Bay, Spain (Ly et al. 2021) reported that concrete mixes with different mortars and recycled aggregates supported different microalgal, macroalgal and invertebrate biomass, depending on the location, but results were not statistically tested. After six months, on average, settlement blocks with geopolymer mortar supported 6 g of algal and invertebrate biomass/block, while blocks with cement mortar supported 7–9 g/block. Biomass was 6–9 g/block with shell-sand aggregate, 6–8 g/block with limestone-sand, and 6–7 g/block with glass-sand. Results varied depending on the location (see paper for location-specific results). Concrete settlement blocks (160 × 40 × 40 mm) were 3D-printed with different mortar (geopolymer, cement) and recycled aggregates (limestone-sand, glass-sand, shell-sand). Nine blocks of each mortar-aggregate combination were attached horizontally to platforms at 1 m depth in each of France, the UK, Portugal and Spain (month/year not reported). Microalgal, macroalgal and invertebrate biomass (dry weight) on blocks was measured in the laboratory over six months.
Study and other actions tested
Referenced paper
Ly O., Yoris-Nobile A.I., Sebaibi N., Blanco-Fernandez E., Boutouil M., Castro-Fresno D., Hall A.E., Herbert R.J.H., Deboucha W., Reis B., Franco J.N., Borges M.T., Sousa-Pinto I., van der Linden P. & Stafford R. (2021) Optimisation of 3D printed concrete for artificial reefs: biofouling and mechanical analysis. Construction and Building Materials, 272, 121649.

Please cite as:

Evans, A.J., Moore, P.J., Firth, L.B., Smith, R.K., and Sutherland, W.J. (2021) Enhancing the Biodiversity of Marine Artificial Structures: Global Evidence for the Effects of Interventions. Conservation Evidence Series Synopses. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

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This Action forms part of the Action Synopsis:

Biodiversity of Marine Artificial Structures

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