Create grooves and small protrusions, ridges or ledges (1–50 mm) on subtidal artificial structures

Overall effectiveness category Awaiting assessment
Number of studies: 3
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not assessed
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not assessed
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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). ‘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 ridges and ledges’ 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). On vertical surfaces, vertically-orientated elevations that fit these criteria are referred to as ‘ridges’, while horizontal ones are referred to as ‘ledges’. On horizontal surfaces, these features are referred to as ‘ridges’ regardless of their orientation.

Grooves, small protrusions, ridges and ledges provide organisms refuge from predation or grazing in subtidal rocky habitats (Nelson & Vance 1979; Wahl & Hoppe 2002). Some species preferentially settle in and around them (Andrews & Anderson 2004; Bourget et al. 1994). The size and density of grooves, protrusions, ridges and ledges 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, limit their growth and get rapidly filled-up (Firth et al. 2020). Large habitats can be used by larger-bodied organisms but may not provide sufficient refuge from predators for smaller organisms. By default, horizontal protrusions/ledges (overhangs) create shaded and downward-facing surfaces, which can be associated with the presence of non-native species (Dafforn 2017).

Grooves, protrusions, ridges and ledges are sometimes present on artificial structures such as cable mattresses (Lacey & Hayes 2020) or quarried boulders (MacArthur et al. 2020), but are often absent from other types of structures. Groove habitats, small protrusions, ridges and ledges can be created on subtidal artificial structures by adding or removing material, either during construction or retrospectively. In some scenarios, creating one will automatically result in creation of the other (i.e. grooves created in between created protrusions/ridges/ledges, or vice versa). Studies containing such scenarios are considered under this joint intervention.

Study locations

Key messages

Three studies examined the effects of creating groove habitats and small protrusions, ridges or ledges on subtidal artificial structures on the biodiversity of those structures. Two studies were in marinas in northern Israel and the UK and one was on an open coastline in southeast Spain.

COMMUNITY RESPONSE (2 STUDIES)

Overall community composition (2 studies): One of two replicated, randomized, controlled studies (including one paired sites, before-and-after study) in Israel and the UK found that groove habitats and small ledges created on a subtidal artificial structure, along with holes and environmentally-sensitive material, altered the combined macroalgae and invertebrate community composition on structure surfaces. They also supported non-mobile invertebrate species that were absent from structure surfaces without added habitat features. One study found that creating grooves and small protrusions had mixed effects on the community composition, depending on the orientation of structure surfaces.
Overall richness/diversity (2 studies): One of two replicated, randomized, controlled studies (including one paired sites, before-and-after study) in Israel and the UK found that creating groove habitats and small ledges on a subtidal artificial structure, along with holes and environmentally-sensitive material, increased the combined macroalgae and invertebrate species richness and diversity on structure surfaces. One study found that creating grooves and small protrusions did not increase the species diversity but had mixed effects on species richness, depending on the orientation of structure surfaces.

POPULATION RESPONSE (1 STUDY)

Overall abundance (1 study): One replicated, randomized, controlled study in the UK found that creating groove habitats and small protrusions on subtidal artificial structures had mixed effects on the combined macroalgae and non-mobile invertebrate abundance, depending on the orientation of structure surfaces.

BEHAVIOUR (1 STUDY)

Use (1 study): One replicated study in Spain reported that groove habitats and small protrusions created on subtidal artificial structures were colonized by macroalgae and non-mobile invertebrates.

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, paired sites, controlled, before-and-after study in 2014–2016 on a subtidal seawall in a marina in the Mediterranean Sea, Israel (Perkol-Finkel et al. 2018) found that groove habitats and small ledges created on seawall panels, along with holes and environmentally-sensitive material, supported higher macroalgae and invertebrate species diversity and richness and different community composition compared with standard-concrete seawall surfaces without added habitats. After 22 months, macroalgae and invertebrate species diversity (data reported as Shannon index) and richness was higher on panels with added habitats (9 species/quadrat) than on seawall surfaces without (5/quadrat), and compared with seawall surfaces before habitats were added (1/quadrat). Community composition differed between panels with added habitats and seawall surfaces without (data reported as statistical model results). Two non-mobile invertebrate species groups recorded on panels were absent from surfaces without. It is not clear whether these effects were the direct result of creating grooves and ledges, holes, or using environmentally-sensitive material. Groove habitats and small ledges were created on seawall panels (height: 1.5 m; width: 0.9 m; thickness: 130 mm) using a formliner. Each panel had multiple interlocking rectangular grooves and ledges (length: 50–150 mm; width/depth/height: 10–50 mm) amongst multiple holes. Panels were made from patented ECOncrete^TM material. Four panels were attached to a vertical concrete seawall in November 2014. The bottom 1.2 m were subtidal. Seawall surfaces were subtidal areas of seawall cleared of organisms (height: 1.2 m; width: 0.9 m) adjacent to each panel. Macroalgae and invertebrates were counted in one 300 × 300 mm randomly-placed quadrat on each panel and seawall surface over 22 months.
Study and other actions tested
Referenced paper
Perkol-Finkel S., Hadary T., Rella A., Shirazi R. & Sella I. (2018) Seascape architecture – incorporating ecological considerations in design of coastal and marine infrastructure. Ecological Engineering, 120, 645-654.
A replicated, randomized, controlled study in 2016 on pontoons in a marina in the Fal estuary, UK (Hanlon et al. 2018) found that upward-facing settlement plates with groove habitats and small protrusions supported different macroalgae and invertebrate community composition, with similar species diversity but higher species richness and abundances, than upward-facing plates without grooves or protrusions, but that there were no significant differences on downward-facing plates. After six months, upward-facing plates with grooves and protrusions supported different macroalgae and invertebrate community composition (data reported as statistical model results) with similar species diversity (data not reported) but higher species richness (20 species/plate, reported from Figure 4) and macroalgae and non-mobile invertebrate live cover (29% cover), compared with plates without grooves and protrusions (15 species/plate, 13% cover). On downward-facing plates, there were no significant differences between plates with and without grooves and protrusions (both 25 species/plate; 92 vs 86% cover). Settlement plates (150 × 150 mm) were moulded with a regular grid of six groove habitats (length: 150 mm; width/depth: 10 mm) between 15 rectangular small protrusions (length: ~44 mm; width: ~22 mm; height: 10 mm) on one surface, but flat on the other. Plates were either standard-concrete or oyster-shell-concrete. Forty plates were suspended horizontally, randomly arranged, beneath floating pontoons at 2–3 m depth in April 2016. Ten of each material had grooves and protrusions facing up, while 10 of each faced down. Macroalgae and invertebrates on upward- and downward-facing surfaces were counted in the laboratory over six months.
Study and other actions tested
Referenced paper
Hanlon N., Firth L.B. & Knights A.M. (2018) Time-dependent effects of orientation, heterogeneity and composition determines benthic biological community recruitment patterns on subtidal artificial structures. Ecological Engineering, 112, 219-228.
A replicated study in 2014–2015 on a subtidal rocky reef on open coastline in the Alboran Sea, Spain (Sempere-Valverde et al. 2018) reported that settlement plates with groove habitats and small protrusions supported 33 macroalgae and non-mobile invertebrate species groups. After 11 months, plates with grooves and protrusions supported 33 species groups in total (20 macroalgae, 13 non-mobile invertebrates). On average, there were nine species/pair of plates, with 55% live cover. Settlement plates (170 × 170 mm) were cut to create a regular grid of six groove habitats (length: 170 mm; width/depth: ~7 mm) between 16 square protrusions (length/width: 30 mm; height: ~7 mm) on their surfaces. Plates were either sandstone, limestone, gabbro, slate or concrete. Two of each material were attached horizontally at 15 m depth on gneiss rocky seabed in each of three sites in June 2014. Macroalgae and non-mobile invertebrates on each pair of plates were counted from photographs over 11 months.
Study and other actions tested
Referenced paper
Sempere-Valverde J., Ostalé-Valriberas E., Farfán G.M. & Espinosa F. (2018) Substratum type affects recruitment and development of marine assemblages over artificial substrata: a case study in the Alboran Sea. Estuarine, Coastal and Shelf Science, 204, 56-65.

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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