Create small protrusions (1–50 mm) on intertidal artificial structures

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

Definition: ‘Small protrusions’ are elevations with a length to width ratio ≤3:1 that protrude 1–50 mm from the substratum (modified from “Small elevations” in Strain et al. 2018).

Small 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 also shelter from predation or grazing (Wahl & Hoppe 2002). Some species preferentially recruit to habitats with high vertical or horizontal relief (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. Small protrusions can be created on intertidal artificial structures by adding material, either during construction or retrospectively.

^{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.}

^{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.}

^{Wahl M. & Hoppe K. (2002) Interactions between substratum rugosity, colonization density and periwinkle grazing efficiency. Marine Ecology Progress Series, 225, 239–249.}

^{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

Two studies examined the effects of creating small protrusions on intertidal artificial structures on the biodiversity of those structures. Both studies were on island coastlines in the Singapore Strait.

COMMUNITY RESPONSE (2 STUDIES)

Overall community composition (2 studies): One of two replicated, randomized, controlled studies in Singapore found that creating small protrusions on intertidal artificial structures did not alter the combined macroalgae and invertebrate community composition on structure surfaces. One study found that creating small protrusions, along with grooves, small ridges and pits, had mixed effects on the community composition, depending on the site and the size and arrangement of protrusions and other habitats.
Overall richness/diversity (2 studies): Two replicated, randomized, controlled studies in Singapore found that creating small protrusions on intertidal artificial structures, along with grooves, small ridges and pits in one study, increased the combined macroalgae and invertebrate species richness on structure surfaces. One of the studies found that varying the size and arrangement of protrusions and other habitats had mixed effects on species richness, depending on the shore level.

POPULATION RESPONSE (2 STUDIES)

Overall abundance (2 studies): One of two replicated, randomized, controlled studies in Singapore found that creating small protrusions on intertidal artificial structures did not increase the combined macroalgae and invertebrate abundance on structure surfaces. One study found that creating small protrusions, along with grooves, small ridges and pits, had mixed effects on abundance, depending on the shore level, site, and the size and arrangement of protrusions and other habitats.

BEHAVIOUR (0 STUDIES)

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 2009–2010 on two intertidal seawalls on island coastlines in the Singapore Strait, Singapore (Loke & Todd 2016a; same experimental set-up as Loke & Todd 2016b) found that concrete settlement plates with small protrusions supported higher macroalgae and invertebrate species richness but similar community composition and abundances compared with granite plates without protrusions. After 13 months, macroalgae and invertebrate species richness was higher on settlement plates with small protrusions (8 species/plate) than without (3/plate), while abundances were statistically similar (88 vs 178 individuals/plate). Community composition was similar on plates with and without protrusions (data reported as statistical model results). Settlement plates (200 × 200 mm) were moulded with and without small protrusions. Plates with protrusions were concrete with 36 cylindrical protrusions/plate with either regular (16 mm width, height and spacing) or variable (4–28 mm) arrangement. Plates without protrusions were granite fragments set in cement. Granite may be considered an environmentally-sensitive material compared with concrete (see “Use environmentally-sensitive material on intertidal artificial structures”). Eight of each design were randomly-arranged at both lowshore and highshore on each of two granite boulder seawalls in November–December 2009. Macroalgae on plates were counted from photographs and invertebrates in the laboratory after 13 months.
Study and other actions tested
Referenced paper
Loke L.H.L. & Todd P.A. (2016) Structural complexity and component type increase intertidal biodiversity independently of area. Ecology, 97, 383-393.
A replicated, randomized, controlled study in 2009–2010 on two intertidal seawalls on island coastlines in the Singapore Strait, Singapore (Loke & Todd 2016b; same experimental set-up as Loke & Todd 2016a) found that concrete settlement plates with small protrusions, along with grooves, small ridges and pits, supported higher macroalgae and invertebrate species richness than granite plates without added habitats, but that abundances and community composition varied depending on the habitat arrangement, shore level and site. After 13 months, macroalgae and invertebrate species richness was higher on settlement plates with protrusions, grooves, ridges and pits than without at lowshore (13–23 vs 6–10 species/plate) and highshore (5–9 vs 2–3/plate). Richness was higher on plates with variable habitats than regular ones at lowshore (22–23 vs 13–16/plate), but not highshore (6–9 vs 5–6/plate). Abundances were higher on plates with added habitats than without in four of eight comparisons (9–833 vs 3–208 individuals/plate), while community composition differed in three of four comparisons (data reported as statistical model results). In all other comparisons, results were similar (abundances: 104–1,957 vs 49–1,162/plate). It is not clear whether these effects were the direct result of creating protrusions, grooves, ridges or pits. However, plate quarters with protrusions had similar richness (8 species/quarter) and abundances (88 individuals/quarter) to quarters with the other habitat types (6–11 species and 97–231 individuals/quarter). Settlement plates (400 × 400 mm) were moulded with and without small protrusions, along with grooves, small ridges and pits. Plates with added habitats were concrete. Each 200 × 200 mm quarter contained either 36 cylindrical protrusions, four-to-five grooves and ridges, 12 ridges or 36 pits. All habitats had either regular (16 mm width, depth/height and spacing) or variable (4–28 mm) arrangement. Plates without added habitats were granite fragments set in cement. Granite may be considered an environmentally-sensitive material compared with concrete (see “Use environmentally-sensitive material on intertidal artificial structures”). Eight of each design were randomly arranged at both lowshore and highshore on each of two granite boulder seawalls in November–December 2009. Macroalgae on plates were counted from photographs and invertebrates in the laboratory after 13 months.
Study and other actions tested
Referenced paper
Loke L.H.L. & Todd P.A. (2016) Structural complexity and component type increase intertidal biodiversity independently of area. Ecology, 97, 383-393.

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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