Create natural rocky reef topography on intertidal artificial structures
Overall effectiveness category Awaiting assessment
Number of studies: 2
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).
See also: Create textured surfaces (≤1 mm) on intertidal artificial structures; Create pit habitats (1–50 mm) on intertidal artificial structures; Create hole habitats (>50 mm) on intertidal artificial structures; Create groove habitats (1–50 mm) on intertidal artificial structures; Create crevice habitats (>50 mm) on intertidal artificial structures; Create ‘rock pools’ on intertidal artificial structures; Create small protrusions (1–50 mm) on intertidal artificial structures; Create large protrusions (>50 mm) on intertidal artificial structures; Create small ridges or ledges (1–50 mm) on intertidal artificial structures; Create large ridges or ledges (>50 mm) on intertidal artificial structures; Create groove habitats and small protrusions, ridges or ledges (1–50 mm) on intertidal artificial structures.
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.
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
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