Create pit habitats (1–50 mm) on subtidal artificial structures

Overall effectiveness category Awaiting assessment
Number of studies: 1
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Background information and definitions

Definition: ‘Pit habitats’ are depressions with a length to width ratio ≤3:1 and depth 1–50 mm (Strain et al. 2018).

Pit habitats provide organisms refuge from predation in subtidal rocky habitats (Nelson & Vance 1979). Some species preferentially settle into them (Nozawa et al. 2011). The size and density of pits is likely to affect the size, abundance and variety of organisms that can use them. Small pits 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 pits can be used by larger-bodied organisms but may not provide sufficient refuge from predators for smaller organisms.

Pits are sometimes present on boulders used in marine artificial structures as a result of quarrying processes (Hall et al. 2018), and can form on other structures through erosion. However, these are often filled or repaired during maintenance works (Moreira et al. 2007) and are absent from many structures. Pit habitats can be created on subtidal artificial structures by adding or removing material, either during construction or retrospectively.

There is a body of literature investigating the effects of creating pit habitats on artificial substrates for coral rearing and gardening (e.g. Nozawa et al. 2011; Okamoto et al. 2010). These studies are not included in this synopsis, which focusses on in situ conservation actions to enhance the biodiversity of structures that are engineered to fulfil a primary function other than providing artificial habitats.

^{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.}

^{Hall A.E., Herbert R.J.H., Britton J.R. & Hull S.L. (2018) Ecological enhancement techniques to improve habitat heterogeneity on coastal defence structures. Estuarine, Coastal and Shelf Science, 210, 68–78.}

^{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.}

^{Nelson B.V. & Vance R.R. (1979) Diel foraging patterns of the sea urchin Centrostephanus coronatus as a predator avoidance strategy. Marine Biology, 51, 251–258.}

^{Nozawa Y., Tanaka K. & Reimer J.D. (2011) Reconsideration of the surface structure of settlement plates used in coral recruitment studies. Zoological Studies, 50, 53–60.}

^{Okamoto M., Yap M., Roeroe A.K., Nojima S., Oyamada K., Fujiwara S. & Iwata I. (2010) In situ growth and mortality of juvenile Acropora over 2 years following mass spawning in Sekisei Lagoon, Okinawa (24°N). Fisheries Science, 76, 343–353.}

^{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.}

Study locations

Key messages

One study examined the effects of creating pit habitats on subtidal artificial structures on the biodiversity of those structures. The study was on an open coastline in northern Israel.

COMMUNITY RESPONSE (1 STUDY)

Overall community composition (1 study): One replicated, controlled study in Israel found that pit habitats created on a subtidal artificial structure, along with holes, grooves and environmentally-sensitive material, altered the combined macroalgae and invertebrate community composition on structure surfaces. They also supported mobile and non-mobile invertebrate and fish species that were absent from a similar structure without the added habitat features.
Overall richness/diversity (1 study): One replicated, controlled study in Israel found that creating pit habitats on a subtidal artificial structure, along with holes, grooves and environmentally-sensitive material, increased the combined macroalgae and invertebrate species diversity on structure surfaces.

POPULATION RESPONSE (1 STUDY)

Algal abundance (1 study): One replicated, controlled study in Israel reported that creating pit habitats on a subtidal artificial structure, along with holes, grooves and environmentally-sensitive material, had mixed effects on macroalgal abundances on structure surfaces, depending on the species group.
Invertebrate abundance (1 study): One replicated, controlled study in Israel reported that creating pit habitats on a subtidal artificial structure, along with holes, grooves and environmentally-sensitive material, had mixed effects on invertebrate abundances on structure surfaces, depending on the species group.
Fish abundance (1 study): One replicated, controlled study in Israel reported that creating pit habitats on a subtidal artificial structure, along with holes, grooves and environmentally-sensitive material, had mixed effects on fish abundances on and around structure surfaces, depending on the species group.

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, controlled study in 2012–2014 on two subtidal breakwaters on open coastline in the Mediterranean Sea, Israel (Sella & Perkol-Finkel 2015) found that pit habitats created on breakwater blocks, along with holes, grooves and environmentally-sensitive material, supported different macroalgae and invertebrate community composition with higher species diversity than standard-concrete blocks without added habitats, while macroalgae, invertebrate and fish abundances varied depending on the species group. After 24 months, the macroalgae and invertebrate species diversity was higher on blocks with added habitats than without (data reported as Shannon index) and the community composition differed (data reported as statistical model results). Thirty species (7 mobile invertebrates, 14 non-mobile invertebrates, 9 fishes) recorded on and around blocks with added habitats were absent from blocks without. Species abundances varied on blocks with and without added habitats depending on the species group (see paper for results). It is not clear whether these effects were the direct result of creating pits, holes, grooves, or using environmentally-sensitive material. Pit habitats were created on breakwater blocks (1 × 1 × 1 m) using a formliner. Each block had multiple round pits (diameter: 10 mm; depth: 5 mm; T. Hadary pers. comms.) amongst multiple holes and grooves (number/spacing not reported). Five blocks of each of three patented ECOncrete^TM materials (lower pH and different cement/additives to standard-concrete) were placed at 5–7 m depth on a concrete-block breakwater during construction in July 2012. Five standard-concrete blocks (1.7 × 1.7 × 1.7 m) without added habitats were placed on a similar breakwater 80 m away. Macroalgae and invertebrates on blocks, and fishes on and around blocks, were counted over 24 months.
Study and other actions tested
Referenced paper
Sella I. & Perkol-Finkel S. (2015) Blue is the new green – ecological enhancement of concrete based coastal and marine infrastructure. Ecological Engineering, 84, 260-272.

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

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This Action forms part of the Action Synopsis:

Biodiversity of Marine Artificial Structures

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