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Providing evidence to improve practice

Action: Create artificial reefs of different 3-D structure and material used Subtidal Benthic Invertebrate Conservation

Key messages

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  • Eight studies examined the effects of creating artificial reefs of different typology on subtidal benthic invertebrate populations. One study was in the English Channel (UK), three in the Mediterranean Sea (Israel, Italy), one in the North Atlantic Ocean (USA), one in the Firth of Lorn (UK), one in the North Pacific Ocean (USA), and one in the Gulf of Mexico (USA).

 

COMMUNITY RESPONSE (6 STUDIES)

  • Overall community composition (3 studies): One controlled study in the English Channel found that artificial reef modules made of scrap tyres developed a similar sessile invertebrate community composition as traditional artificial concrete modules. Two controlled studies (one replicated) in the Mediterranean Sea found that pyramids reefs made of “sea-friendly” concrete developed different invertebrate community compositions compared to reefs of either traditional concrete plinth-pole structures or bundles of traditional concrete tubes.
  • Overall richness/diversity (5 studies): Four controlled studies (three replicated) in the Mediterranean Sea, the North Pacific Ocean, and the Gulf of Mexico found no differences in overall invertebrate richness/diversity or combined mobile invertebrate and fish richness between reef structure and/or material. One controlled study in the Mediterranean Sea found that invertebrate species richness was lower on “sea-friendly” pyramid reefs compared to bundle reefs of traditional concrete.

POPULATION RESPONSE (7 STUDIES)

  • Overall abundance (5 studies): Four controlled studies (three replicated) in the English Channel, the Mediterranean Sea, the North Pacific Ocean, and the Gulf of Mexico found no differences in overall invertebrate abundances or combined mobile invertebrate and fish abundance between reef structure and/or material. One controlled study in the Mediterranean Sea found that “sea-friendly” concrete pyramids had lower abundance compared to plinth-pole structures after two years, but higher after three.
  • Crustacean abundance (2 studies): One replicated, controlled study in the North Atlantic Ocean found that artificial reefs made of limestone boulders, gravel concrete aggregate, or tyre-concrete aggregate had similar abundance of spiny lobsters. One replicated, controlled study in the Firth of Lorn found that the complexity of artificial reef modules had mixed effects on the abundance of edible crab and velvet swimming crab.
  • Mollusc abundance (1 study): One replicated, controlled study in the Gulf of Mexico found that breakwaters made of bags of oyster shells recruited more oysters and ribbed mussels compared to “ReefBall” breakwaters.

Supporting evidence from individual studies

1 

A controlled study in 1998–1999 of an unclear number of artificial reef modules in Poole Bay, English Channel, UK (Collins et al. 2002) found that modules made of scrap tyres developed a similar sessile invertebrate community composition and species percentage cover compared to traditional artificial concrete modules, 10–11 months after deployment. Tetrahedral and cylindrical tyre modules had similar community composition to concrete modules (community data presented as graphical analyses). Tetrahedral and cylindrical tyre modules also had similar species groups percentage cover compared to concrete modules (see paper for specific groups). In July 1998, artificial modules (number unclear) arranged in eight groups were put on the seabed as artificial reefs alongside a pre-existing coal ash artificial reef. Each group had replicate modules of each of three reef types: tetrahedral tyre lattice (4–13 tyres/module), cylindrical tyre stack (6–7 tyres/module), or traditional concrete block (no tyres). Every two month until June 1999, divers photographed the sides of the modules (8 photographs/module), and invertebrate growing on them were identified, and their percentage cover assessed.

2 

A replicated, controlled study in 1996–1999 of 80 artificial reef blocks in the southeastern Mediterranean Sea, off the coast of Haifa, Israel (Kress et al. 2002) found that blocks created using coal fly ash (a cheap waste product) instead of sand had similar sessile invertebrate species richness and percentage cover as traditional blocks without coal fly ash, over 33 months following deployment. When compared to blocks made of traditional 0% coal fly ash, reef blocks made of either 40%, 60% or 80% coal fly ash had similar species richness (in 22 of 24 comparisons) and similar species cover (in 24 of 24 comparisons) (data not shown). In November 1996, blocks (20 × 20 × 40 cm) made of a mixture of concrete and coal fly ash were put on the seabed as artificial reefs at 18.5 m depth. There were four treatments: blocks with either 0%, 40%, 60% and 80% coal fly ash (20 blocks/treatment). Divers sampled two blocks/treatment at 3–4-month intervals for 33 months (10 sampling events). Invertebrates growing on each block side were identified and counted, and their percentage cover estimated.

3 

A replicated, controlled study in 1998–2001 of 12 artificial reefs in one sandy area off Miami Beach, Florida, North Atlantic Ocean, USA (Walker et al. 2002) found that artificial reefs constructed with either of one of three types of material had similar abundance of spiny lobsters Panulirus argus. Total spiny lobster abundance was similar at reefs made of limestone boulders (16), gravel-concrete aggregate (16), and tyre-concrete aggregate (14). Between June and August 1998, twelve artificial reefs constructed with either limestone boulders, gravel-concrete aggregate, or tyre-concrete aggregate (four of each) were created at 7 m water depth. Every two months between October 1998 and February 2001, one diver recorded the total abundance of spiny lobster at each reef.

4 

A replicated, controlled study in 2005–2006 of six sites with artificial reef modules in the Firth (Lynn) of Lorn, west coast of Scotland, UK (Hunter & Sayer 2009) found that the complexity of the modules had mixed effects on the abundances of edible crab Cancer pagurus and velvet swimming crab Necora puber, which varied with the seasons. For edible crabs, abundances in summer and autumn were similar at all modules (0–0.05/m2). In winter, abundance was higher at complex modules (0.13/m2), than simple modules (0.04/m2). In spring, abundance at complex modules (0.15/m2) was not significantly higher than at simple modules (0.04/m2). For swimming crabs, abundance in summer was similar at both module types (0.15–0.27/m2). In all other seasons, abundance was higher at complex modules (0.34–0.45/m2), than simple modules (0.05–0.18/m2). In 2003–2004, an artificial reef complex made of multiple modules of either simple solid concrete blocks or complex perforated blocks was created. Six sites were surveyed: three simple modules and three complex modules. Monthly in August 2005–June 2006, divers recorded edible and swimming crab abundances along two 9 m2 belt transect/site. Data were grouped by season. A prior study showed that habitat complexity was higher on complex modules than simple modules.

5 

A controlled study in 2005–2008 of an artificial reef complex made of pyramids and plinth-poles created on soft seabed 3 nm off the coast of Italy, Mediterranean Sea (Spagnolo et al. 2014) found that during the three years following creation, “sea-friendly” concrete pyramids developed a significantly different invertebrate community composition compared to traditional concrete plinth-pole structures. Invertebrate community composition remained dissimilar between the two structure types over the three years (year 1: 40% similarity; year 2: 73%; year 3: 68%). For the first two years, pyramids had lower invertebrate species richness (average 10 species) and abundance (average 2 individuals/dm2) compared to plinth-pole structures (richness: 27; abundance: 48). After three years, pyramids had similar species richness (27) and higher abundance (85) compared to plinth-pole structures (richness: 24; abundance: 33). Diversity (reported as a diversity index) was lower on pyramids after a year compared to plinth-pole structures, higher after two, and not different after three. In 2005, the Pedaso artificial reef, made of 76 pyramids of “sea-friendly” concrete slabs surrounded by 214 plinth-pole structures made of traditional concrete (aimed at preventing illegal trawling), was created at 15 m depth (see paper for details on reef architecture). Invertebrates colonizing the reef were surveyed in summer in 2006, 2007 and 2008 (three surveys/year). During each survey, divers scraped a 40 × 40 cm area on the external vertical sides of three randomly-chosen structures for each reef type, and invertebrates (>0.5 mm) were identified, counted and weighed.

6 

A replicated, controlled study in 2006–2012 of an unspecified number of artificial reefs made of pyramids and tubes created on muddy seabed 2 nm offshore of the Po River Delta, northern Mediterranean Sea, Italy (Ponti et al. 2015) found that “sea-friendly” concrete pyramid reefs developed a different invertebrate community composition compared to bundle reefs of traditional concrete tubes, after 2–6 years depending on creation year. For reefs deployed in 2006, pyramid reefs had similar communities to bundle reefs by 2009, but different ones by 2012. For reefs deployed in 2010, pyramid reefs developed different communities to bundle reefs by 2012. Community data were presented as graphical analyses. In addition, at all times, species richness was higher on bundle reefs (38–55 species/sample) compared to pyramid reefs (33–45 species/sample). In 2006 and 2010, artificial reefs made of either pyramids of “sea-friendly” concrete slabs or bundles of traditional concrete tubes were created at 13–14 m depths (see paper for details). Divers surveyed the external sides of four randomly-chosen structures for each reef type in 2009 and 2012. For each structure, invertebrates were identified and counted from four 20 × 20 cm quadrats. They were also identified, and their percent cover estimated from six photographs/structure (21 × 26 cm).

7 

A replicated, controlled study in summer 2000 and 2004 of one artificial reef made of modules off southern California, North Pacific Ocean, USA (Schroeter et al. 2015) found that from one to five years after their deployment, there was no difference in species richness or abundance (as % cover) of invertebrates growing on modules made of granite and those made of concrete (results presented as statistical model output). The artificial reef was created to compensate for the loss of giant kelp forest in California. Low lying (<1 m tall) artificial reef modules (40 × 40 m) made of either granite boulders of concrete rubble boulders were put on the seabed in seven sites in 1999 (4 modules/material/site) at 13–16 m depth. Invertebrate communities were sampled after one and five years. Invertebrate abundance was assessed for 42 of the 56 modules using six 1 m2 quadrats/modules.

8 

A replicated, controlled study in 2008–2010 of four artificial breakwaters in northwest Mobile Bay, Gulf of Mexico, Alabama, USA (Scyphers et al. 2015) found that breakwaters made of bags of oyster shells recruited more oysters and ribbed mussels, but did not have different species richness and abundance of small mobile animal species (invertebrates and fish combined, referred to as “nekton”), compared to “ReefBall” breakwaters, during the two years following deployment. More eastern oysters Crassostrea virginica were recorded on shell breakwaters (20 in total) than on ReefBall breakwaters (2) throughout the study period (data not statistically tested). On average across the study period, significantly more ribbed mussels Geukensia demissa were recorded on shell breakwaters (>2,500/m2) than on ReefBall breakwaters (14/m2). Across the study period, shell and ReefBall breakwaters had similar nekton species richness (shell: 2.3; ReefBall: 2.2 species/m2) and abundance (shell: 0.46; ReefBall: 0.46 individual/m2). Four artificial breakwaters made of either bags of clean oyster shells (2,000 bags/breakwater) or ReefBall modules (three rows of 41 modules/breakwater), acting as artificial reefs, were created in May 2008 along an eroding shoreline in Mobile Bay (60 m from, and parallel to, the shore; 0.75m depth). On three occasions in 2008–2010, nine modules/ReefBall breakwater and nine bags/shell breakwater were sampled. The surface area of each modules and the content of each bag were examined for live oysters and mussels. Between May 2008 and November 2009, nekton was surveyed on each side of all breakwaters using a bag seine (6.25 mm mesh) deployed over 12.5 m. All organisms were identified and counted.

Referenced papers

Please cite as:

Lemasson, A.J., Pettit, L.R., Smith, R.K., and Sutherland, W.J. (2019) Subtidal Benthic Invertebrate Conservation: Global Evidence for the Effects of Interventions. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.