Create hole habitats (>50 mm) on intertidal artificial structures

Overall effectiveness category Awaiting assessment
Number of studies: 5
Share Tweet Email

View assessment score

How is the evidence assessed?

Effectiveness

not assessed
Certainty

not assessed
Harms

not assessed

Calculating overall effectiveness category

Background information and definitions

Definition: ‘Hole habitats’ are depressions with a length to width ratio ≤3:1 and depth >50 mm (modified from “Subtidal holes” in Strain et al. 2018). Intertidal hole habitats do not retain water during low tide – those that do would come under the action “Create ‘rock pools’ on intertidal artificial structures”. The two actions can be combined (e.g. pools created in holes).

Hole habitats provide organisms refuge from desiccation and temperature fluctuations during low tide in intertidal rocky habitats (Williams & Morrit 1995). They also provide shelter from predation or grazing (Menge & Lubchenco 1981). The size and density of holes is likely to affect the size, abundance and variety of organisms that can use them. Small holes 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 holes can be used by larger-bodied organisms but may not provide sufficient refuge from predators for smaller organisms. By default, holes contain shaded surfaces, which can be associated with the presence of non-native species (Dafforn 2017).

Holes are sometimes present on boulders used in marine artificial structures as a result of quarrying processes or engineering tests (Firth et al. 2014). However, these are sparse when present and are normally absent from other types of structures. Holes sometimes form on artificial structures through erosion, but are often filled or repaired during maintenance works (Moreira et al. 2007). Hole habitats can be created on intertidal artificial structures by adding or removing 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.}

^{Firth L.B., Airoldi L., Bulleri F., Challinor S., Chee S.-Y., Evans A.J., Hanley M.E., Knights A.M., O’Shaughnessy K., Thompson R.C. & Hawkins S.J. (2020) Greening of grey infrastructure should not be used as a Trojan horse to facilitate coastal development. Journal of Applied Ecology, 57, 1762–1768.}

^{Firth L.B., Thompson R.C., Bohn K., Abbiati M., Airoldi L., Bouma T.J., Bozzeda F., Ceccherelli V.U., Colangelo M.A., Evans A., Ferrario F., Hanley M.E., Hinz H., Hoggart S.P.G., Jackson J.E., Moore P., Morgan E.H., Perkol-Finkel S., Skov M.W., Strain E.M., van Belzen J. & Hawkins S.J. (2014) Between a rock and a hard place: environmental and engineering considerations when designing coastal defence structures. Coastal Engineering, 87, 122–135.}

^{Menge B.A. & Lubchenco J. (1981) Community organization in temperate and tropical rocky intertidal habitats: prey refuges in relation to consumer pressure gradients. Ecological Monographs, 51, 429–450.}

^{Moreira J., Chapman M.G. & Underwood A.J. (2007) Maintenance of chitons on seawalls using crevices on sandstone blocks as habitat in Sydney Harbour, Australia. Journal of Experimental Marine Biology and Ecology, 347, 134–143.}

^{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.}

Study locations

Key messages

Five studies examined the effects of creating hole habitats on intertidal artificial structures on the biodiversity of those structures. Three studies were in estuaries in southeast Australia and the UK, one was on an open coastline in the Netherlands, and one was in a marina in northern Israel.

COMMUNITY RESPONSE (3 STUDIES)

Overall community composition (3 studies): One replicated, randomized, paired sites, controlled, before-and-after study in Israel found that creating hole habitats on an intertidal artificial structure, along with grooves, small ridges and environmentally-sensitive material, altered the combined macroalgae and invertebrate community composition on structure surfaces. The study, along with two other replicated, controlled studies in Australia and the UK, also reported that hole habitats, along with rock pools, or grooves, small protrusions and environmentally-sensitive material, supported macroalgae and/or non-mobile invertebrate species that were absent from structure surfaces without added habitat features.
Overall richness/diversity (3 studies): Three replicated, controlled studies (including one randomized, paired sites, before-and-after study) in Australia, the UK and Israel found that creating hole habitats on intertidal artificial structures, along with rock pools, or grooves, small protrusions and environmentally-sensitive material, increased the combined macroalgae and invertebrate species diversity and/or richness on structure surfaces.

POPULATION RESPONSE (2 STUDIES)

Algal abundance (1 study): One replicated, paired sites, controlled study in the Netherlands reported that creating hole habitats on an intertidal artificial structure did not increase the macroalgal abundance on structure surfaces.
Invertebrate abundance (2 studies): One of two replicated, controlled studies (including one paired sites study) in Australia and the Netherlands reported that creating hole habitats on an intertidal artificial structure did not increase the invertebrate abundance on structure surfaces. One study found that creating holes, along with rock pools, had mixed effects on the limpet abundance, depending on the shore level and site.

BEHAVIOUR (1 STUDY)

Use (1 study): One study in Australia reported that hole habitats created on an intertidal artificial structure, along with rock pools, were used by sea slugs, urchins and octopuses.

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, controlled study in 2006–2007 on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Blockley 2009) reported that hole habitats created on the seawall, along with rock pools, supported higher macroalgae and non-mobile invertebrate species richness than seawall surfaces without holes or pools, and found that limpet Siphonaria denticulata abundance varied depending on the shore level and site. After 12–14 months, holes supported 2–31 macroalgae and non-mobile invertebrate species groups/site (highshore: 2–10/site; midshore: 16–18/site; lowshore: 27–31/site), while seawall surfaces without holes or pools supported 2–21/site (highshore: 2–3/site; midshore: 7–11/site; lowshore: 19–21/site) (data not statistically tested). At least 14 species (≥5 macroalgae, ≥9 non-mobile invertebrates) recorded in holes were absent from surfaces without. Limpet abundances varied by shore level and site (see paper for results). It is not clear whether these effects were the direct result of creating holes or rock pools. Hole habitats were created during July–September 2006 by replacing seawall blocks with water-retaining troughs during construction of a vertical sandstone seawall. Six cuboidal holes (length: 600 mm; height/depth: 300 mm) were created at highshore, midshore, and lowshore in each of three sites along the seawall. Hole surfaces were sandstone and concrete. Water pooled to 50 mm in the base of holes but wet surfaces were not surveyed. Holes were compared with six seawall surfaces (length: 600 mm; height: 300 mm) at each shore level and site. Macroalgae and invertebrates were counted in holes and on seawall surfaces during low tide in September 2007.
Study and other actions tested
Referenced paper
Chapman M.G. & Blockley D.J. (2009) Engineering novel habitats on urban infrastructure to increase intertidal biodiversity. Oecologia, 161, 625-635.
A study (year not reported) on an intertidal seawall in Sydney Harbour estuary, Australia (Chapman & Underwood 2011) reported that hole habitats created on the seawall, along with rock pools, were used by mobile invertebrates from at least three species groups. Sea slugs (Opistobranchia), urchins (Echinoidea) and octopuses (Octopoda) were recorded in holes and pools. It is not clear whether these effects were the direct result of creating holes or rock pools. Hole habitats were created, along with rock pools, by replacing seawall blocks with sandbags during maintenance of a vertical sandstone seawall, then removing the sandbags to leave shaded water-retaining depressions in the wall. No other details were reported.
Study and other actions tested
Referenced paper
Chapman M.G. & Underwood A.J. (2011) Evaluation of ecological engineering of “armoured” shorelines to improve their value as habitat. Journal of Experimental Marine Biology and Ecology, 400, 302-313.
A replicated, controlled study in 2010–2011 on an intertidal seawall in the Teign estuary, UK (Firth et al. 2014) found that hole habitats created on the seawall, along with rock pools, supported higher macroalgae and invertebrate species richness than seawall surfaces without holes or pools. After 19 months, macroalgae and invertebrate species richness was higher in holes (3 species/hole) than on seawall surfaces without (1/surface). Barnacles (Cirripedia) were recorded only in holes. It is not clear whether these effects were the direct result of creating holes or rock pools. Hole habitats were created in May 2010 by replacing seawall blocks with water-retaining troughs during construction of a vertical sandstone seawall. Fifteen cube-shaped holes (150 × 150 × 150 mm) were created at highshore. Water pooled in the base of holes (depth/volume not reported). Holes were compared with 15 mortar seawall surfaces (150 × 150 mm). Macroalgae and invertebrates were counted in holes and on seawall surfaces during low tide after 19 months. Three holes and seven surfaces had been buried by sediment and no longer provided habitat.
Study and other actions tested
Referenced paper
Firth L.B., Thompson R.C., Bohn K., Abbiati M., Airoldi L., Bouma T.J., Bozzeda F., Ceccherelli V.U., Colangelo M.A., Evans A.J., Ferrario F., Hanley M.E., Hinz H., Hoggart S.P.G., Jackson J.E., Moore P., Morgan E.H., Perkol-Finkel S., Skov M.W., Strain E.M., van Belzen J. & Hawkins S.J. (2014) Between a rock and a hard place: environmental and engineering considerations when designing coastal defence structures. Coastal Engineering, 87, 122-135.
A replicated, paired sites, controlled study in 2008–2010 on an intertidal breakwater on open coastline in the North Sea, Netherlands (Paalvast 2015) reported that settlement plates with hole habitats supported similar abundances of macroalgae and invertebrates to plates without holes. Data were not statistically tested. After 28 months, there were no clear differences in macroalgal or invertebrate abundances on plates with and without holes (data not reported). Concrete settlement plates (250 × 250 mm) were made with and without hole habitats using a mould. Plates with holes had one hemispherical hole/plate (diameter: 150 mm; depth: 50 mm). One plate with a hole and one without were placed on each of 10 horizontal surfaces on each side of a concrete-block breakwater (wave-exposed, wave-sheltered) in May 2008. On the wave-exposed side, plates were at mid-highshore, while on the wave-sheltered side, plates were at low-midshore. Macroalgae and invertebrates on plates were counted during low tide over 28 months.
Study and other actions tested
Referenced paper
Paalvast P. (2015) The role of geometric structure and texture on concrete for algal and macrofaunal colonization in the marine and estuarine intertidal zone. RECIF Conference on artificial reefs: From materials to ecosystems, Caen, France, 77-84.
A replicated, randomized, paired sites, controlled, before-and-after study in 2014–2016 on an intertidal seawall in a marina in the Mediterranean Sea, Israel (Perkol-Finkel et al. 2018) found that hole habitats created on seawall panels, along with grooves, small ledges 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 (8 species/quadrat) than on seawall surfaces without (3/quadrat), and compared with seawall surfaces before habitats were added (2/quadrat). Community composition differed between panels with added habitats and seawall surfaces without (data reported as statistical model results). Five species groups (1 macroalgae, 4 non-mobile invertebrates) recorded on panels were absent from surfaces without. It is not clear whether these effects were the direct result of creating holes, grooves, ledges, or using environmentally-sensitive material. Hole habitats were created on seawall panels (height: 1.5 m; width: 0.9 m; thickness: 130 mm) using a formliner. Each panel had six cylindrical holes (diameter: 30 mm; depth: 120 mm; ≥300 mm apart) amongst multiple grooves and small ledges. Panels were made from patented ECOncrete^TM material. Four panels were attached to a vertical concrete seawall in November 2014. The top 0.3 m were intertidal. Seawall surfaces were intertidal areas of seawall cleared of organisms (height: 0.3 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 during high tide 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.

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?

List of journals searched by synopsis

All the journals searched for all synopses

This Action forms part of the Action Synopsis:

Biodiversity of Marine Artificial Structures

Related Actions

Actions	Effectiveness	Studies	Category
Create crevice habitats (>50 mm) on intertidal artificial structures Action Link	No evidence found (no assessment)	0	Synopsis Link
Create small adjoining cavities or ‘swimthrough’ habitats (≤100 mm) on intertidal artificial structures Action Link	Awaiting assessment	2	Synopsis Link
Create large adjoining cavities or ‘swimthrough’ habitats (>100 mm) on intertidal artificial structures Action Link	No evidence found (no assessment)	0	Synopsis Link