Create large protrusions (>50 mm) on intertidal artificial structures
Overall effectiveness category Awaiting assessment
Number of studies: 2
Background information and definitions
Definition: ‘Large protrusions’ are elevations with a length to width ratio ≤3:1 that protrude >50 mm from the substratum (modified from “Large elevations” in Strain et al. 2018).
Large protrusions create vertical or horizontal (i.e. overhangs) relief in intertidal rocky habitats. They can provide organisms refuge from desiccation and temperature fluctuations during low tide (Williams & Morrit 1995) and alter flow velocities (Guichard & Bourget 1998). Some species preferentially recruit to habitats with high vertical or horizontal relief, potentially to avoid predators (Harmelin-Vivien et al. 1995). The size and density of protrusions is likely to affect the size, abundance and variety of organisms that can use them. Small habitats can provide refuge for small-bodied organisms but may exclude larger organisms and limit their growth. Large habitats can be used by larger-bodied organisms but may not provide sufficient refuge from predators for smaller organisms. By default, horizontal protrusions (overhangs) create shaded and downward-facing surfaces, which can be associated with the presence of non-native species (Dafforn 2017).
Protrusions are sometimes present on quarried boulders used in marine artificial structures (MacArthur et al. 2020) but are often absent from other types of structures. Large protrusions can be created on intertidal artificial structures by adding material, either during construction or retrospectively.
See also: Create textured surfaces (≤1 mm) on intertidal artificial structures; Create natural rocky reef topography on intertidal artificial structures; Create small protrusions (1–50 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.
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.
Guichard F. & Bourget E. (1998) Topgraphic heterogeneity, hydrodynamics, and benthic community structure: a scale-dependence cascade. Marine Ecology Progress Series, 171, 59–70.
Harmelin-Vivien M.L., Harmelin J.G. & Leboulleux V. (1995) Microhabitat requirements for settlement of juvenile sparid fishes on Mediterranean rocky shores. Hydrobiologia, 300, 309–320.
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.
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.
Williams G.A. & Morritt D. (1995) Habitat partitioning and thermal tolerance in a tropical limpet, Cellana grata. Marine Ecology Progress Series, 124, 89–103.
Supporting evidence from individual studies
A replicated, controlled study in 2015–2017 on an intertidal seawall on open coastline in the UK (MacArthur et al. 2020) found that boulders positioned with large protrusions on their upper surfaces, along with large ridges, supported similar macroalgae and invertebrate species richness and barnacle Semibalanus balanoides abundance, but higher limpet Patella vulgata abundance, than boulders positioned randomly. Boulders positioned with large protrusions and ridges on their upper surfaces supported similar macroalgae and invertebrate species richness (4 species/boulder) and barnacle abundance (data not reported) but more limpets (82 limpets/boulder) than boulders positioned randomly (4 species/boulder, 27 limpets/boulder). It is not clear whether these effects were the direct result of creating large protrusions or ridges. Ten granite boulders (width: 2 m) were intentionally positioned with naturally-occurring large protrusions and/or ridges on their upper surfaces (average 4/boulder) and ten were positioned randomly (1/boulder) at mid-highshore in a granite boulder seawall during construction in 2015–2017. Protrusions/ridges were 100–800 mm high (other dimensions/spacing not reported). Macroalgae and invertebrates on the upper surfaces of boulders were counted during low tide in June 2017.Study and other actions tested
A replicated, randomized, controlled study in 2014–2016 on an intertidal seawall in a marina in the Coral Sea, Australia (Waltham & Sheaves 2018) reported that large protrusions created on the seawall supported similar macroalgae and invertebrate species richness to seawall surfaces without protrusions, but that tilted protrusions with shaded surfaces supported different community composition to horizontal ones. Over 24 months, a total of nine macroalgae and invertebrate species groups were recorded on landward-tilted protrusions, eight on seaward-tilted protrusions, eight on horizontal protrusions, and 10 on seawall surfaces without protrusions (data not statistically tested). Community composition was similar on landward- and seaward-tilted protrusions, but both differed to horizontal protrusions (data reported as statistical model results). Four species (3 mobile invertebrates, 1 non-mobile invertebrate) recorded on protrusions were absent from seawall surfaces without. Large protrusions were created by attaching concrete troughs to a boulder seawall in June 2014. Troughs contained rock pools but outside surfaces were surveyed separately and constituted protrusions lacking a top surface. Rectangular protrusions (length: 400 mm; width: 250 mm; height: 350 mm) were either horizontal or tilted 45° towards the land or sea. Underhanging surfaces of tilted protrusions were shaded. There were three of each randomly arranged at midshore along the seawall. Macroalgae and invertebrates were counted on protrusions and seawall surfaces (number/dimensions not reported) during low tide over 24 months. One horizontal protrusion was missing and no longer provided habitat.Study and other actions tested