Create groove habitats (1–50 mm) on intertidal artificial structures

Overall effectiveness category Awaiting assessment
Number of studies: 14
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Background information and definitions

Definition: ‘Groove habitats’ are depressions with a length to width ratio >3:1 and depth 1–50 mm (modified from “Crevices” in Strain et al. 2018).

Groove habitats provide organisms refuge from desiccation and temperature fluctuations during low tide in intertidal rocky habitats (Williams & Morrit 1995). They also provide shelter from predation or grazing (Menge & Lubchenco 1981) and some species preferentially settle into them (Chabot & Bourget 1988). The size and density of grooves is likely to affect the size, abundance and variety of organisms that can use them. Small grooves can provide refuge for small-bodied organisms but may exclude larger organisms, limit their growth and get rapidly filled-up (Firth et al. 2020). Large grooves can be used by larger-bodied organisms but may not provide sufficient refuge from predators for smaller organisms.

Grooves are sometimes present on boulders used in marine artificial structures as a result of quarrying processes (MacArthur et al. 2020). They can also form on structures through erosion, but will often be filled or repaired during maintenance works (Moreira et al. 2007), and are absent from many structures (Aguilera et al. 2014). Groove habitats can be created on intertidal artificial structures by adding or removing material, either during construction or retrospectively.

There is a body of literature investigating the effects of creating groove habitats on experimental artificial substrates on the recruitment and survival of intertidal rocky shore species (e.g. Savoya & Schwindt 2010; van Tamelen et al. 1997). These studies are not included in this synopsis, which focusses on in situ conservation actions to enhance the biodiversity of marine artificial structures.

^{Aguilera M.A., Broitman B.R. & Thiel M. (2014) Spatial variability in community composition on a granite breakwater versus natural rocky shores: lack of microhabitats suppresses intertidal biodiversity. Marine Pollution Bulletin, 87, 257–268.}

^{Chabot R. & Bourget E. (1988) Influence of substratum heterogeneity and settled barnacle density on the settlement of cypris larvae. Marine Biology, 97, 45–56.}

^{Firth L.B., Airoldi L., Bulleri F., Challinor S., Chee S.-Y., Evans A.J., Hanley M.E., Knights A.M., O’Shaughnessy K., Thompson R.C. & Hawkins S.J. (2020) Greening of grey infrastructure should not be used as a Trojan horse to facilitate coastal development. Journal of Applied Ecology, 57, 1762–1768.}

^{MacArthur M., Naylor L.A., Hansom J.D. & Burrows M.T. (2020) Ecological enhancement of coastal engineering structures: passive enhancement techniques. Science of the Total Environment, 740, 139981.}

^{Menge B.A. & Lubchenco J. (1981) Community organization in temperate and tropical rocky intertidal habitats: prey refuges in relation to consumer pressure gradients. Ecological Monographs, 51, 429–450.}

^{Moreira J., Chapman M.G. & Underwood A.J. (2007) Maintenance of chitons on seawalls using crevices on sandstone blocks as habitat in Sydney Harbour, Australia. Journal of Experimental Marine Biology and Ecology, 347, 134–143.}

^{Savoya V. & Schwindt E. (2010) Effect of the substratum in the recruitment and survival of the introduced barnacle Balanus glandula (Darwin 1854) in Patagonia, Argentina. Journal of Experimental Marine Biology and Ecology, 382, 125–130.}

^{Strain E.M.A., Olabarria C., Mayer-Pinto M., Cumbo V., Morris R.L., Bugnot A.B., Dafforn K.A., Heery E., Firth L.B., Brooks P.R. & Bishop M.J. (2018) Eco-engineering urban infrastructure for marine and coastal biodiversity: which interventions have the greatest ecological benefit? Journal of Applied Ecology, 55, 426–441.}

^{van Tamelen P.G., Stekoll M.S. & Deysher L. (1997) Recovery processes of the brown alga Fucus gardneri following the ‘Exxon Valdez’ oil spill: settlement and recruitment. Marine Ecology Progress Series, 160, 265–277.}

^{Williams G.A. & Morritt D. (1995) Habitat partitioning and thermal tolerance in a tropical limpet, Cellana grata. Marine Ecology Progress Series, 124, 89–103.}

Study locations

Key messages

Fourteen studies examined the effects of creating groove habitats on intertidal artificial structures on the biodiversity of those structures. Seven studies were in estuaries in southeast Australia, the UK and Hong Kong, four were on open coastlines in the UK and the Netherlands, two were on island coastlines in the Singapore Strait, and one was in a port in the Netherlands.

COMMUNITY RESPONSE (11 STUDIES)

Overall community composition (3 studies): Two of three replicated, controlled studies (including one randomized and two before-and-after studies) in Australia and the UK found that creating groove habitats on intertidal artificial structures did not alter the combined macroalgae and invertebrate community composition on structure surfaces. However, one of these studies reported that grooves supported macroalgae, mobile and non-mobile invertebrate species that were absent from structure surfaces without grooves. One study found that creating grooves did alter the community composition.
Fish community composition (1 study): One replicated, randomized, controlled study in Singapore found that groove habitats created on an intertidal artificial structure, along with pits, altered the fish community composition on and around structure surfaces, and supported species that were absent from surfaces without grooves and pits.
Overall richness/diversity (8 studies): Three of six replicated, controlled studies (including two randomized and two before-and-after studies) in the UK and Singapore found that creating groove habitats on intertidal artificial structures, along with pits in one study, increased the combined macroalgae and invertebrate species richnessand/or diversity on structure surfaces. Two studies found that creating grooves did not increase their species richness. One found that creating grooves, along with pits, had mixed effects on species richness depending on the site. One of the studies found that increasing the density and fragmentation of grooves, along with pits, had mixed effects on species richness. Two replicated studies (including one randomized, paired sites study) in Hong Kong and Australia found that grooves supported higher species richness than small ridges or ledges created in between them, but one found that species diversity in grooves vs ridges varied depending on the groove depth.
Algal richness/diversity (1 study): One replicated, paired sites, controlled study in Australia found that creating groove habitats on intertidal artificial structures did not increase the macroalgal species richness on structure surfaces.
Invertebrate richness/diversity (3 studies): Two replicated, controlled studies (including one randomized and one paired sites study) in Australia found that creating groove habitats on intertidal artificial structures did not increase the species richness of mobile or non-mobile invertebrates or limpets on structure surfaces. One replicated study in Australia found that grooves supported higher mobile invertebrate species richness than small ledges created in between them.
Fish richness/diversity (2 studies): One replicated, randomized, controlled study in Singapore found that creating groove habitats on an intertidal artificial structure, along with pits, increased the fish species richness on and around structure surfaces. One replicated study in Australia found that grooves supported similar fish species richness to small ledges created in between them.

POPULATION RESPONSE (9 STUDIES)

Overall abundance (4 studies): Two of three replicated, controlled studies (including one randomized and two before-and-after studies) in the UK and Singapore found that creating groove habitats on intertidal artificial structures, along with pits in one study, increased the combined macroalgae and invertebrate abundance on structure surfaces. One found that creating grooves did not increase their abundance. One replicated study in Australia found that grooves supported similar abundances to small ledges created in between them.
Algal abundance (2 studies): Two replicated, paired sites, controlled studies in the Netherlands reported that creating groove habitats on intertidal artificial structures did not increase the macroalgal abundance on structure surfaces.
Invertebrate abundance (6 studies): Three of four replicated, controlled studies (including two randomized and two paired sites studies) in Australia, the Netherlands and the UK found that creating groove habitats on intertidal artificial structures did not increase the invertebrate, limpet or chiton abundances on structure surfaces. One study found that creating grooves, along with pits, had mixed effects on mobile invertebrate and barnacle abundances, depending on the site. One replicated, paired sites, controlled study in Australia reported that grooves supported non-mobile invertebrates more frequently than structure surfaces without grooves, but not mobile invertebrates. One replicated study in Australia found that grooves supported higher mobile invertebrate and oyster abundances than small ledges created in between them.
Fish abundance (2 studies): One replicated, randomized, controlled study in Singapore found that creating groove habitats on an intertidal artificial structure, along with pits, increased the fish abundance on and around structure surfaces. One replicated study in Australia found that grooves supported similar fish abundance to small ledges created in between them.

BEHAVIOUR (2 STUDIES)

Use (1 study): One replicated, paired sites, controlled study in the Netherlands reported that groove habitats created on an intertidal artificial structure were used by mussels and periwinkles.
Fish behaviour change (1 study): One replicated, randomized, controlled study in Singapore found that creating groove habitats on an intertidal artificial structure, along with pits, increased the number of bites fishes took from structure surfaces.

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, controlled study in 2000–2003 on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Underwood 2011a) found that creating groove habitats on the seawall did not alter the macroalgae and invertebrate community composition or increase limpet (Patellidae and/or Siphonariidae, Fissurellidae) species richness or abundance, or chiton (Polyplacophora) abundance on seawall surfaces. After three months, seawall surfaces with grooves supported similar macroalgae and invertebrate community composition to surfaces without (data reported as statistical model results). After 27 months, limpet species richness and abundance were similar in grooves (0 species and individuals/array) and on surfaces without (1 species/surface, 3 individuals/surface). The same was true for chiton abundance (grooves: 0 individuals/array; surfaces: 0/surface). Groove habitats were created in 2000 (month not reported) by drilling into a vertical sandstone seawall during reconstruction. Arrays of 16 grooves (length: 50 mm; width: 10 mm; depth: 5 mm; spacing/orientation not reported) were drilled on 1 × 0.4 m seawall surfaces. There were five surfaces with grooves and five without randomly arranged (shore level not reported). Macroalgae and invertebrates were counted on surfaces with and without grooves during low tide after three months. Mobile invertebrates were counted in grooves and on surfaces without after 27 months.
Study and other actions tested
Referenced paper
Chapman M.G. & Underwood A.J. (2011) Evaluation of ecological engineering of “armoured” shorelines to improve their value as habitat. Journal of Experimental Marine Biology and Ecology, 400, 302-313.
A replicated, paired sites, controlled study (year not reported) on two intertidal seawalls in Sydney Harbour estuary, Australia (Chapman & Underwood 2011b; same experimental set-up as Dugan et al. 2011) reported that creating groove habitats on the seawalls had mixed effects on invertebrate abundances depending on the species group and shore level, but data were not statistically tested. Over 12 months, both grooves and seawall surfaces without grooves supported mobile invertebrates (data not reported) and non-mobile invertebrates at midshore (mussels Mytilus galloprovincialis planulatis: recorded in grooves in 65% of surveys vs seawall surfaces in 27%; sponges (Porifera): 10 vs 4%; barnacles (Cirripedia): 26 vs 16%; tubeworms (Polychaeta): 34 vs 26%) and lowshore (mussels: 50 vs 33%; sponges: 20 vs 13%; sea squirts (Ascidiacea): 4 vs 3%; tubeworms: 44 vs 49%). Groove habitats were created by indenting wet mortar between blocks during maintenance of vertical sandstone seawalls (month/year not reported). Five grooves (width: 30–50 mm; depth: 20 mm; length/orientation/spacing not reported) were compared with five flat mortar surfaces (dimensions not reported) at both midshore and lowshore in each of two paired sites on each of two seawalls. Invertebrates were counted in grooves and on surfaces without during low tide over 12 months, on 10 occasions on one seawall and seven on the other.
Study and other actions tested
Referenced paper
Chapman M.G. & Underwood A.J. (2011) Evaluation of ecological engineering of “armoured” shorelines to improve their value as habitat. Journal of Experimental Marine Biology and Ecology, 400, 302-313.
A replicated, paired sites, controlled study (year not reported) on two intertidal seawalls in Sydney Harbour estuary, Australia (Dugan et al. 2011; same experimental set-up as Chapman & Underwood 2011b) found that groove habitats created on the seawalls supported similar macroalgae and invertebrate species richness to seawall surfaces without grooves. Over 12 months, macroalgal species richness was similar in grooves and on surfaces without at lowshore (grooves: 7–8 species/survey; surfaces: 6–9/survey) and midshore (7–8 vs 5–7/survey). The same was true for mobile invertebrates (lowshore: grooves and surfaces both 0–1/survey; midshore: both 2–3/survey) and non-mobile invertebrates (lowshore: 4–6 vs 3–5/survey; midshore: 5–6 vs 3–5/survey). Groove habitats were created by indenting wet mortar between blocks during maintenance of vertical sandstone seawalls (month/year not reported). Five grooves (width: 30–50 mm; depth: 20 mm; length/orientation/spacing not reported) were compared with five flat mortar surfaces (dimensions not reported) at both midshore and lowshore in each of two paired sites on each of two seawalls. Macroalgae and invertebrates were counted in grooves and on surfaces without during low tide over 12 months, on nine occasions on one seawall and seven on the other. Method details reported from Chapman & Underwood 2011b.
Study and other actions tested
Referenced paper
Dugan J.E., Airoldi L., Chapman M.G., Walker S.J. & Schlacher T. (2011) Estuarine and coastal structures: environmental effects, a focus on shore and nearshore structures. Pages 17-41 in: E. Wolanski & D.S. McLusky (eds.) Treatise on Estuarine and Coastal Science. 8, Academic Press, Waltham, Massachusetts.
A replicated, controlled study in 2010–2011 on an intertidal seawall in the Teign estuary, UK (Firth et al. 2014a) found that groove habitats created on the seawall supported similar macroalgae and invertebrate species richness to seawall surfaces without grooves. After 19 months, macroalgae and invertebrate species richness was similar in grooves (1 species/array) and on surfaces without grooves (1/surface). Groove habitats were created in May 2010 by scraping a trowel across wet mortar between blocks during construction of a vertical sandstone seawall. Arrays of 5–10 grooves (length: 150 mm; width/depth: 1–5 mm) were irregularly-spaced on 150 × 150 mm seawall surfaces. There were 15 surfaces with grooves and 15 without at highshore. Macroalgae and invertebrates were counted in grooves and on surfaces without during low tide after 19 months. Two arrays of grooves and seven surfaces without had been buried by sediment and no longer provided habitat.
Study and other actions tested
Referenced paper
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.J., Ferrario F., Hanley 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, 122-135.
A replicated, controlled study in 2012─2013 on an intertidal groyne on open coastline in the Irish Sea, UK (Firth et al. 2014b) reported that groove habitats created on a concrete block placed in the groyne supported similar macroalgae and invertebrate species richness to groyne surfaces without grooves. Data were not statistically tested. After 13 months, a total of four species were recorded in grooves and on groyne surfaces without grooves. Groove habitats were created on two vertical sides of a concrete block (1.5 × 1.5 × 1 m) using a mould. Ten horizontal grooves (length: 1 m; width/depth: 50 mm) were cast 50 mm apart on each side. The block was placed at midshore in a boulder groyne during construction in February 2012. Surfaces with grooves were compared with vertical surfaces of adjacent groyne boulders (dimensions/material not reported). Macroalgae and invertebrates were counted in grooves and on groyne surfaces without during low tide after 13 months.
Study and other actions tested
Referenced paper
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.J., Ferrario F., Hanley 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, 122-135.
A replicated, paired sites, controlled study in 2008–2010 on an intertidal breakwater on open coastline in the North Sea, Netherlands (Paalvast 2015a) reported that settlement plates with groove habitats supported similar abundances of macroalgae and invertebrates to plates without grooves. Data were not statistically tested. After 28 months, there were no clear differences in macroalgal or invertebrate abundances on plates with and without grooves (data not reported). Blue mussels Mytilus edulis and periwinkles Littorina saxatilis and Littorina neritoides were seen using grooves. Concrete settlement plates (250 × 250 mm) were made with and without groove habitats using a mould. Plates with grooves had five variable grooves/plate (length: 250 mm; width: 10–35 mm; depth: 20–40 mm) in horizontal or vertical orientation. One of each orientation and one plate without grooves were placed on each of 10 horizontal and 10 vertical surfaces on each side of a concrete-block breakwater (wave-exposed, wave-sheltered) in May 2008. On the wave-exposed side, plates were at mid-highshore, while on the wave-sheltered side, plates were at low-midshore. Macroalgae and invertebrates on plates were counted during low tide over 28 months.
Study and other actions tested
Referenced paper
Paalvast P. (2015) The role of geometric structure and texture on concrete for algal and macrofaunal colonization in the marine and estuarine intertidal zone. RECIF Conference on artificial reefs: From materials to ecosystems, Caen, France, 77-84.
A replicated, paired sites, controlled study in 2009 on 14 jetty pilings in Rotterdam Port in the Rhine-Meuse estuary, Netherlands (Paalvast 2015b) reported that settlement plates with groove habitats supported similar abundances of macroalgae and invertebrates to plates without grooves. Data were not statistically tested. After nine months, there were no clear differences in macroalgal or invertebrate abundances on plates with and without grooves (data not reported). Concrete settlement plates (250 × 250 mm) were made with and without groove habitats using a mould. Plates with grooves had five variable grooves/plate (length: 250 mm; width: 10–35 mm; depth: 20–40 mm) in horizontal orientation. One plate with grooves and one without were attached to vertical surfaces on each of 14 wooden pilings at lowshore in March 2009. Macroalgae and invertebrates on plates were counted during low tide over nine months.
Study and other actions tested
Referenced paper
Paalvast P. (2015) The role of geometric structure and texture on concrete for algal and macrofaunal colonization in the marine and estuarine intertidal zone. RECIF Conference on artificial reefs: From materials to ecosystems, Caen, France, 77-84.
A replicated, controlled, before-and-after study in 2014–2015 on an intertidal seawall on open coastline in the North Sea, UK (Hall et al. 2018a) found that creating groove habitats on the seawall altered the macroalgae and invertebrate community composition and increased their species diversity, richness and abundance on seawall surfaces. After 12 months, the macroalgae and invertebrate species diversity (data reported as Shannon index) was similar on seawall surfaces with and without grooves, but higher than on surfaces before grooves were created. Species richness and abundance were higher on surfaces with grooves (5 species/surface, 183 individuals/surface) than without (2 species/surface, 12 individuals/surface), and also compared with before grooves were created (0 species and individuals/surface). Community composition differed on surfaces with and without grooves (data reported as statistical model results). Groove habitats were created by cutting into vertical surfaces of a granite boulder seawall. Arrays of nine horizontal grooves (length: 600 mm; width: 3–20 mm; depth: 10 mm) were irregularly-spaced on 600 × 600 mm seawall surfaces. There were seven surfaces with grooves and seven without at mid-lowshore. Organisms were removed from surfaces when grooves were created in October 2014, then macroalgae and invertebrates were counted on surfaces with and without grooves during low tide over 12 months.
Study and other actions tested
Referenced paper
Hall A.E., Herbert R.J.H., Britton J.R. & Hull S.L. (2018) Ecological enhancement techniques to improve habitat heterogeneity on coastal defence structures. Estuarine, Coastal and Shelf Science, 210, 68-78.
A replicated, controlled, before-and-after study in 2015–2016 on two intertidal groynes on open coastline in the English Channel, UK (Hall et al. 2018b) found that creating groove habitats on the groynes increased the macroalgae and invertebrate species diversity and richness on groyne surfaces, but did not increase their abundance or alter the community composition. After 12 months, the macroalgae and invertebrate species diversity (data reported as Shannon index) was similar on groyne surfaces with and without grooves, but higher than on surfaces before grooves were created. Species richness was higher on surfaces with grooves (5 species/surface) than without (2/surface), and also compared with before grooves were created (1/surface). Abundances were similar on surfaces with grooves (55 individuals/surface) and without (75/surface) to surfaces before grooves were created (71/surface). Twelve species (5 macroalgae, 4 mobile invertebrates, 3 non-mobile invertebrates) recorded on surfaces with grooves were absent from those without, but the community composition was similar (data reported as statistical model results). Groove habitats were created by cutting into vertical surfaces of two limestone boulder groynes. Arrays of nine horizontal grooves (length: 600 mm; width: 3–20 mm; depth: 10 mm) were irregularly-spaced on 600 × 600 mm groyne surfaces. There were 24 surfaces with grooves and 24 without at lowshore. Organisms were removed from surfaces when grooves were created in March 2015, then macroalgae and invertebrates were counted on surfaces with and without grooves during low tide over 12 months.
Study and other actions tested
Referenced paper
Hall A.E., Herbert R.J.H., Britton J.R. & Hull S.L. (2018) Ecological enhancement techniques to improve habitat heterogeneity on coastal defence structures. Estuarine, Coastal and Shelf Science, 210, 68-78.
A replicated, randomized, controlled study in 2014–2015 on an intertidal seawall on an island coastline in the Singapore Strait, Singapore (Loke et al. 2019) found that creating groove habitats on the seawalls, along with pits, increased the macroalgae and invertebrate species richness on seawall surfaces, and that increasing the density and fragmentation of grooves and pits had mixed effects on species richness. After 12 months, macroalgae and invertebrate species richness was higher on seawall surfaces with grooves and pits (13–29 species/surface) than on surfaces without (3/surface). Species richness varied on surfaces with high-density (19–29/surface), medium-density (14–27/surface) and low-density (13–16/surface) grooves and pits, depending on their arrangement, and vice versa (unfragmented arrangement: 14–20/surface; moderately-fragmented: 13–29/surface; highly-fragmented: 15–20/surface). It is not clear whether these effects were the direct result of creating grooves or pits. Concrete settlement plates (200 × 200 mm) were moulded with seven groove habitats amongst 37 pits, both with variable length, width and depth (2–56 mm). Plates with grooves and pits were attached to 2.4 × 2.4 m seawall surfaces in varying densities (high: 30 plates/surface; medium: 20/surface; low: 10/surface) and arrangement (unfragmented, moderately-fragmented, highly-fragmented). Four surfaces with each density-fragmentation combination and four with no plates were randomly arranged, spanning low-highshore, on a granite boulder seawall in February 2014. Macroalgae on seawall surfaces with and without plates were counted from photographs and invertebrates in the laboratory after 12 months.
Study and other actions tested
Referenced paper
Loke L.H.L., Chisholm R.A. & Todd P.A. (2019) Effects of habitat area and spatial configuration on biodiversity in an experimental intertidal community. Ecology, 100, e02757.
A replicated, randomized, controlled study in 2016–2017 on two intertidal seawalls in the Clyde and Forth estuaries, UK (MacArthur et al. 2019) found that creating groove habitats on the seawalls, along with pits, had mixed effects on the macroalgae and invertebrate species richness and invertebrate abundances, depending on the site. After 18 months, at one of two sites, macroalgae and mobile invertebrate species richness and mobile invertebrate abundances were higher on settlement plates with grooves and pits (4 species/plate, 11 individuals/plate) than without (1 species/plate, 1 individual/plate), but barnacle (Cirripedia) cover was similar on plates with and without grooves and pits (15 vs 22%). At the second site, richness and mobile invertebrate abundances were similar on plates with and without grooves and pits (2 vs 1 species/plate, both 3 individuals/plate), while barnacle cover was lower on plates with grooves and pits (73 v 83%). It is not clear whether these effects were the direct result of creating grooves or pits. Concrete settlement plates (150 × 150 mm) were moulded with and without groove habitats and pits. Plates with grooves and pits had seven grooves amongst 37 pits, both with variable dimensions (maximum depth: 30 mm). Eight plates with grooves and pits and eight without were randomly arranged at upper-midshore on each of two vertical concrete seawalls in April–May 2016. Macroalgae and invertebrates on plates were counted from photographs over 18 months.
Study and other actions tested
Referenced paper
MacArthur M., Naylor L., Hansom J.D., Burrows M.T., Loke L.H.L. & Boyd I. (2019) Maximising the ecological value of hard coastal structures using textured formliners. Ecological Engineering, 142S, 100002.
A replicated, randomized, paired sites study in 2016–2017 on two intertidal seawalls in the Pearl River estuary, Hong Kong (Bradford et al. 2020) found that groove habitats created on the seawalls supported higher macroalgae and invertebrate species richness than small ridges created in between them, while species diversity varied depending on the groove depth. After 12 months, macroalgae and invertebrate species richness on settlement plates was similar in deep (8–9 species/plate) and shallow (9/plate) grooves, and higher in both than on the ridges in between (both 3–4/plate). The same was true for species diversity, except that deep grooves supported similar diversity to ridges (data reported as Shannon index). Concrete settlement plates (250 × 250 mm) were moulded with four deep (depth: 50 mm) or shallow (25 mm) vertical groove habitats (length: 250 mm; width: 15–50 mm) between five small ridges (length: 250 mm; width: 17–65 mm; height: 50 or 25 mm). Five of each were randomly arranged at midshore on each of two vertical concrete seawalls in November 2016 (month/year: M. Perkins pers. comms.). Plates had textured surfaces. Macroalgae and invertebrates in grooves and on ridges were counted in the laboratory after 12 months. One plate with deep grooves was missing and no longer provided habitat.
Study and other actions tested
Referenced paper
Bradford T.E., Astudillo J.C., Lau E.T.C., Perkins M.J., Lo C.C., Li T.C.H., Lam C.S., Ng T.P.T., Strain E.M.A., Steinberg P.D. & Leung K.M.Y. (2020) Provision of refugia and seeding with native bivalves can enhance biodiversity on vertical seawalls. Marine Pollution Bulletin, 160, 111578.
A replicated study in 2015–2016 on two intertidal seawalls in Sydney Harbour estuary, Australia (Strain et al. 2020) found that groove habitats created on the seawalls supported higher macroalgae and invertebrate species richness and higher mobile invertebrate and oyster Saccostrea glomerata abundances than small ledges created in between them, but that macroalgae and other non-mobile invertebrate abundance, fish species richness and fish abundance were similar in grooves and on ledges. After 12 months, grooves supported higher macroalgae and non-mobile invertebrate species richness (6 species/groove) than the ledges in between (4/ledge). The same was true for mobile invertebrates (6/groove vs 4/ledge), but not fishes (both 2/sample). Abundances were higher in grooves than on ledges for mobile invertebrates (18 individuals/groove vs 1/ledge) and oysters (56 vs 14% cover), but were similar for macroalgae and other non-mobile invertebrates (38 vs 36% cover) and fishes (both 1 individual/sample). Concrete settlement plates (250 × 250 mm) were moulded with four horizontal groove habitats (length: 250 mm; width: 15–50 mm; depth: 50 mm) between five small ledges (length: 250 mm; width: 17–65 mm; height: 50 mm). Five plates were attached at midshore on each of two vertical sandstone seawalls in November 2015. Plates had textured surfaces. Macroalgae and invertebrates were counted in grooves and on ledges during low tide, from photographs and in the laboratory after 12 months. Fishes were counted from time-lapsed photographs during two high tides.
Study and other actions tested
Referenced paper
Strain E.M.A., Cumbo V.R., Morris R.L., Steinberg P.D. & Bishop M.J. (2020) Interacting effects of habitat structure and seeding with oysters on the intertidal biodiversity of seawalls. PLoS ONE, 15, e0230807.
A replicated, randomized, controlled study in 2018–2019 on an intertidal seawall on an island coastline in the Singapore Strait, Singapore (Taira et al. 2020) found that creating groove habitats on the seawall, along with pits, increased the macroalgae and non-mobile invertebrate abundance, fish species richness and abundance, and altered the fish community composition and behaviour on and around seawall surfaces. After 12 months, macroalgae and non-mobile invertebrate abundance was higher on seawall surfaces with grooves and pits (17% cover) than on surfaces without (4%). Over 12 months, fish community composition differed on and around surfaces with and without grooves and pits (data reported as statistical model results). Fish species richness and maximum abundance were higher on and around surfaces with grooves and pits (9–15 species and 14–29 individuals/60-minute survey) than without (7–14 species/survey, 10–25 individuals/survey), and fishes took more bites from surfaces with grooves and pits (18–456 vs 4–17 bites/survey). Eleven fish species recorded on and around surfaces with grooves and pits were absent from those without. It is not clear whether these effects were the direct result of creating grooves or pits. Concrete settlement plates (200 × 200 mm) were moulded with seven groove habitats amongst 37 pits, both with variable length, width and depth (2–56 mm). Twenty plates with grooves and pits were attached to 2.4 × 2.4 m seawall surfaces in seven irregularly-spaced patches. Plates had been naturally-colonized since February 2015. Six surfaces with plates and six without were randomly arranged, spanning low-highshore, on a granite boulder seawall in February 2018. Macroalgae and non-mobile invertebrates on seawall surfaces with and without plates were counted from photographs, while fishes and the number of bites they took were counted from 60-minute videos during each of seven high tides over 12 months.
Study and other actions tested
Referenced paper
Taira D., Heery E.C., Loke L.H.L., Teo A., Bauman A.G. & Todd P.A. (2020) Ecological engineering across organismal scales: trophic-mediated positive effects of microhabitat enhancement on fishes. Marine Ecology Progress Series, 656, 181-192.

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

Related Actions

Actions	Effectiveness	Studies	Category
Create small ridges or ledges (1–50 mm) on intertidal artificial structures Action Link	Awaiting assessment	4	Synopsis Link
Create natural rocky reef topography on intertidal artificial structures Action Link	Awaiting assessment	2	Synopsis Link
Create large protrusions (>50 mm) on intertidal artificial structures Action Link	Awaiting assessment	2	Synopsis Link