Create natural rocky reef topography on intertidal artificial structures

Overall effectiveness category Awaiting assessment
Number of studies: 2
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Background information and definitions

Definition: ‘Natural rocky reef topography’ refers to the full fingerprint of substrate topography found in natural rocky habitats.

Topography influences the settlement and survival of marine organisms on intertidal rocky substrates. Variation in topography generates variation in the physical environment and plays an important role in sustaining biodiversity and ecological functioning (Levin 1974). On rocky reefs, many habitat features that offer refuge from physical stressors and predation, such as bumps, crevices and holes, are generated as a function of substrate topography and geomorphology. The full fingerprint of natural rocky reef topography encompasses a variety of habitat features of different scales interacting within a mosaic.

Marine artificial structures often have much lower topographic variability than natural rocky reefs, which is thought to be a key reason for their reduced biodiversity (Firth et al. 2013; Moschella et al. 2005). Natural rocky reef topography can be created on intertidal artificial structures by moulding or casting material during construction or retrospectively (see Evans et al. 2021).

^{Evans A.J., Lawrence P.J., Natanzi A.S., Moore P.J., Davies A.J., Crowe T.P., McNally C., Thompson B., Dozier A.E. & Brooks P.R. (2021) Replicating natural topography on marine artificial structures – a novel approach to eco-engineering. Ecological Engineering, 160, 106144.}

^{Firth L.B., Thompson R.C., White F.J., Schofield M., Skov M.W., Hoggart S.P.G., Jackson J., Knights A.M. & Hawkins S.J. (2013) The importance of water-retaining features for biodiversity on artificial intertidal coastal defence structures. Diversity and Distributions, 19, 1275–1283.}

^{Levin S.A. (1974) Dispersion and population interactions. American Society of Naturalists, 108, 207–228.}

^{Moschella P.S., Abbiati M., Åberg P., Airoldi L., Anderson J.M., Bacchiocchi F., Bulleri F., Dinesen G.E., Frost M., Gacia E., Granhag L., Jonsson P.R., Satta M.P., Sundelöf A., Thompson R.C. & Hawkins S.J. (2005) Low-crested coastal defence structures as artificial habitats for marine life: using ecological criteria in design. Coastal Engineering, 52, 1053–1071.}

Study locations

Key messages

Two studies examined the effects of creating natural rocky reef topography on intertidal artificial structures on the biodiversity of those structures. One study was on an open coastline and in estuaries in the UK, and one was on an open coastline in the UK.

COMMUNITY RESPONSE (1 STUDY)

Overall richness/diversity (1 study): One replicated, randomized, controlled study in the UK found that creating natural rocky reef topography on intertidal artificial structures did not increase the combined macroalgae and invertebrate species richness on structure surfaces.

POPULATION RESPONSE (1 STUDY)

Invertebrate abundance (1 study): One replicated, randomized, controlled study in the UK found that creating natural rocky reef topography on intertidal artificial structures had mixed effects on barnacle and mobile invertebrate abundances on structure surfaces, depending on the site.

BEHAVIOUR (1 STUDY)

Use (1 study): One study in the UK reported that natural topography created on intertidal artificial structures was colonized by macroalgae and limpets, and that limpets used shaded grooves and water-retaining depressions created by the topography.

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 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 creating natural rocky reef topography on the seawalls did not increase the macroalgae and invertebrate species richness on seawall surfaces, but increased invertebrate abundances at one of three sites. After 18 months, macroalgae and mobile invertebrate species richness was similar on settlement plates with and without natural rocky reef topography (both 1 species/plate). Barnacle (Cirripedia) and mobile invertebrate abundances were higher on plates with topography than without at one site (barnacles: 72 vs 34% cover; mobiles: 3 vs 1 individuals/plate), but were statistically similar at two sites (barnacles: 48–93 vs 22–83%; mobiles: 1 vs 2–3/plate). Concrete settlement plates (150 × 150 mm) were made with and without natural rocky reef topography moulded from digital scans of a natural boulder surface. Eight plates with topography and eight without were randomly arranged at upper-midshore on each of three 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 study in 2019 on two intertidal breakwaters on open coastline in the Irish Sea, UK (Evans et al. 2021) reported that natural rocky reef topography created on the breakwaters supported macroalgae (Ulva spp.) and limpets (Patella spp.). Over four months, green macroalgae and adult and juvenile limpets were recorded on settlement plates with natural rocky reef topography. Limpets were seen using shaded grooves and water-retaining depressions created by the natural topography. Concrete settlement plates (250 × 250 mm) were made with natural rocky reef topography moulded from digital scans of natural reef surfaces. Natural surfaces were selected based on the biodiversity they supported and measured features of the underlying topography. They were designed to target high species richness, rare species, or species that were common on natural reefs but not on artificial structures. Plates with natural topography were attached on horizontal surfaces of two granite boulder breakwaters in August 2019 (A. Evans, pers. comms.). Macroalgae and invertebrates on plates were counted during low tide over four months.
Study and other actions tested
Referenced paper
Evans A.J., Lawrence P.J., Natanzi A.S., Moore P.J., Davies A.J., Crowe T.P., McNally C., Thompson B., Dozier A.E. & Brooks P.R. (2021) Replicating natural topography on marine artificial structures - a novel approach to eco-engineering. Ecological Engineering, 160, 106144.

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.

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This Action forms part of the Action Synopsis:

Biodiversity of Marine Artificial Structures

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Create natural rocky reef topography on intertidal artificial structures Action Link	Awaiting assessment	2	Synopsis Link