Use settlement tiles made from unnatural materials to encourage natural coral settlement
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Overall effectiveness category Awaiting assessment
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Number of studies: 16
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Supporting evidence from individual studies
A replicated study in 1994–1995 at two reef sites at Heron Reef, Great Barrier Reef, Australia (Mundy 2000) found that attaching artificial settlement tiles directly to the substrate did not result in higher natural coral recruitment than tiles attached in pairs or singly to wire mesh racks. Five months after tiles were installed, there was no significant difference between the number of coral recruits on tiles attached to the substrate (Site 1: 1.4, Site 2: 1.2/100 cm2), pairs of tiles on wire racks (Site 1: 1.3, Site 2: 1.4/100 cm2) or single tiles on racks (Site 1: 1.3, Site 2: 1.5/100 cm2). In September 1994, forty unglazed terracotta settlement tiles (110 × 110 × 10 mm) with numerous pits and grooves (<1 × 1 mm) were taken to each of two reef sites 500 m apart. Tiles (10/site) were screwed to a stainless-steel baseplate (100 × 50 × 0.6 mm) and attached to the substrate 1 – 2 m apart using two screws. Wire mesh, A-frame racks (five/site) were anchored to the substrate 2–3 m apart, 9 m deep using steel pegs. One pair of tiles (one on top of the other) and one single tile were screwed to each side of the A-frame (30 tiles/site). Plates and racks were retrieved in February 1995 and the number of coral recruits was counted using a microscope.
Study and other actions testedA replicated study in 1994–1995 at two reef sites at Heron Reef, Great Barrier Reef, Australia (Mundy 2000) reported that attaching artificial settlement tiles to the substrate on different natural substrate features, depths, and at different angles led to natural coral settlement. Five months after tiles were installed, the number of acroporid coral recruits ranged from 0–4/tile at both sites, and pocilloporid coral recruits ranged from 0–16/tile at Site 1 and 0–11/tile at Site 2 (data reported as statistical model results). In September 1994, unglazed terracotta settlement tiles (110 × 110 × 10 mm) with numerous pits and grooves (<1 × 1 mm) were attached to stainless steel base plates and screwed to the substrate at two reef sites (site 1: 228 tiles; site 2: 206 tiles). Tiles were attached on different topographic features categorized as ‘level’ (flat substrate); ‘protected’ (located in a depression >5 cm below surrounding substrate); ‘raised’ (on mound >10 cm above substrate); ‘stepped’ (located on a series of ledges). Tiles were placed at different angles (0–90° and depths (2.5–8.7 m). Tiles were collected after five months, and the number of coral recruits was counted and identified.
Study and other actions testedA randomized, replicated study in 1998 on sandy substrate at a coral reef at Danjugan Island, Sulu Sea, central Philippines (Reyes & Yap 2001), found that a higher number of stony coral larvae settled on tiles made from consolidated coral rubble or concrete than rubber, and more coral larvae settled on tiles placed within compared to outside an existing reef. After 4.5 months, the average number of stony coral larvae/tile was higher on coral rubble (within reef: 7.7; outside reef: 2.9) and concrete (within reef: 6.9; outside reef: 2.3) than rubber (within reef: 0.45; outside reef: 0.35) tiles and higher on tiles within the existing reef than outside. Almost all settled larvae were from two families (Pocilloporids: 87% within, 88% outside; Acroporids: 11% within, 12% outside). In February 1998, forty-eight 10 × 10 cm tiles comprising 16 each of coral-rubble-cement, concrete, and rubber were randomly arranged on 16 frames (one of each type/frame) and attached using wire ties. Eight frames were placed within an existing coral reef <0.25 m from live coral, and eight placed outside the reef area >5 m from live coral. Frames were placed 12 m deep, 30 cm above the sandy seabed. Frames were retrieved after 4.5 months and larvae were counted and identified under a microscope.
Study and other actions testedA replicated, site comparison study in 1997–1999 at two coral reef sites in Amakusa, Japan (Tioho et al. 2001) found that placing artificial settlement tiles adjacent to adult stony coral Pocillopra damicornis colonies led to higher recruitment than tiles placed 8–10 m away. Three months after larvae were released by the adult colonies, 70 recruits had settled on tiles in July–October 1997 and 65 in July–October 1998 but no recruits settled NovemberJune in 1998 or 1999. The study reports that there were significantly more recruits on tiles placed adjacent to adult P. damicornis colonies than on tiles placed 8–10 m away but numbers are not reported. In July 1997, fifteen concrete blocks (40 × 20 × 10 cm) were placed on the substrate, adjacent (5–10 cm) to existing Pocillopora damicornis colonies, and a further 15 blocks were placed 810 m away from the nearest colony. Six ceramic settlement tiles (10 × 10 × 2 cm) were bolted to each concrete block. Tiles were retrieved after three months and new plates were attached and retrieved in June 1998. The process was repeated from July 1998–June 1999. P. damicornis recruits were identified and counted under a microscope.
Study and other actions testedA replicated study in 1998–2002 on rocky substrate in Leghorn, Italy (Bramanti et al. 2005) found that marble settlement tiles were settled on by Mediterranean red coral Corallium rubrum larvae and some survived and grew, with survival similar between depths. Overall, 388 new coral colonies settled on tiles during the four-year study (244 on tiles 25 m deep and 144 at 35 m). After four years, coral density was 19 (at 25 m) and 10 (at 35 m) settlers/10 cm2. Average annual survival of cohorts (survival rate between two consecutive years) was similar across the study period and between depths (76% at 25 m; 75% at 35 m). After four years, 34% (25 m) and 31% (35 m) of the first cohorts (settled in 1998) had survived. Average diameter increased with coral age (1 year old: 0.6; 4 years old: 2.5 mm), height also increased with age (2 years old: 2mm; 4 years old: 7 mm). The average number of polyps was significantly higher for four-year-old corals (38) than two (9) and one (5) year old. In June 1998 (approximately three weeks before red coral spawning), 20 white marble tiles (90 × 120 mm) were fixed with a steel screw into crevices at 25 m and 35 m depth (10/depth). Tiles were monitored every three months from October 1998–October 2002 when they were removed and red coral settlers counted and measured.
Study and other actions testedA replicated, site comparison study in 2003–2004 at two sites in Italy and one in Spain (Bramanti et al. 2007) found that using marble settlement tiles resulted in recruitment of red coral Corallium rubrum with settlement rates, recruitment density and mortality rates varying depending on site. Four months after tiles were installed, there was no significant difference in overall settlement rate between sites (Calafuria: 67%; Elba: 50%; Medes: 50%). Average settler recruitment density varied between sites (Calafuria: 2.8; Elba: 1.1; Medes 1.6 recruits / dm2). One year after installation, average mortality rates varied between sites with 72% (21/29) mortality at Mendes, 14% (7/50) mortality at Calafuria, and 10% (2/20) mortality at Elba. In June 2003, fifty-four marble tiles (9 × 12 cm) were secured using a single central screw to rocky crevices on vertical cliffs 25–35 m deep. Nine tiles were placed at each of two locations in three sites in the Mediterranean (Calafuria and Elba, Italy; Mendes, Spain). Settlement by red coral recruits was photographed and analysed after four months (October 2003) and mortality rate measured after a year (June 2004).
Study and other actions testedA replicated study in 1999–2001 at a shallow reef in Eilat, Israel (6a) found that using unglazed ceramic settlement tiles resulted in a higher number of naturally settled hard coral spat (settled larvae) compared to brick tiles but only during the third survey period and no difference in the number of naturally settled soft coral spat. Four months after the third deployment of tiles, there were 255 hard coral and 153 soft coral spat on 66 tiles. Numbers of naturally settled hard coral spat were higher on ceramic tiles (4 – 10/100 cm2) compared to brick tiles (3 – 4/100 cm2). There was no difference for soft coral spat (ceramic: 1 – 2/100 cm2; brick: 1 – 2/100 cm2). There were 34 hard and 81 soft coral spat recorded four months after the second deployment of tiles but no difference between ceramic or brick tiles. No coral spat was recorded during the first survey period. In November 1999, June 2000, and March 2001, nine unglazed ceramic (100 × 100 × 5 mm) and nine fired brick (115 × 115 × 25 mm) settlement tiles were fixed to the substrate using masonry plugs, and nine of each type attached to one of three wire racks. Tiles were placed 10 – 20 mm (masonry plug) or 200 – 400 mm (wire rack), above the substrate, 5 m deep. Tiles were recovered and replaced four months after each deployment. Coral spat was counted and species groups recorded using a dissecting microscope.
Study and other actions testedA replicated study in 1999–2001 at a shallow reef in Eilat, Israel (Field et al. 2007) found that settlement tiles attached to wire racks had a higher number of naturally settled hard coral spat (settled larvae) compared to tiles attached to the substrate but only during the third survey period and no difference in the number of naturally settled soft coral spat. Four months after the third deployment of tiles, there were 255 hard coral and 153 soft coral spat on 66 tiles. Numbers of naturally settled coral spat were higher on tiles attached to a wire rack (4 – 10/100 cm2) compared to tiles attached directly to the substrate (3– 4/100 cm2). There was no difference for soft coral spat (wire rack: 1 – 2; substrate: 1 – 2/100cm2). There were 34 hard and 81 soft coral spat recorded four months after the second deployment of tiles but no difference between tiles on the rack or the substrate. No coral spat was recorded during the first survey period. In November 1999, June 2000, and March 2001, eighteen settlement tiles (nine 100 × 100 × 5 mm unglazed ceramic; nine 115 × 115 × 25 mm fired brick) were attached using cable ties to one of three wire racks fixed 200–400 mm above the substrate at a 45° angle, 5 m deep. Eighteen tiles were attached to the substrate 5 m deep using masonry plugs leaving a gap of 10 – 20 mm. Tiles were recovered and replaced after four months. Coral spat was counted and species groups recorded using a dissecting microscope.
Study and other actions testedA replicated, randomized, controlled study in 2007–2008 on two artificial reefs and two rocky reefs off Dubai, United Arab Emirates (7) found that sandstone, terracotta, granite, gabbro, and concrete settlement tiles had similar densities of settled corals at three of four sites. At one of four sites, juvenile corals were more abundant on gabbro (8 corals/100 cm2) than sandstone (3 corals/100 cm2) and concrete (3 corals/100 cm2) tiles, and more abundant on terracotta (7 corals/100 cm2) than sandstone, with other comparisons showing no differences (granite: 5 corals/100 cm2). At the other sites, few corals were recorded with no significant differences between materials (<1 coral/100 cm2 at all). Settlement tiles (100 × 100 × 15 mm) were made from sandstone, terracotta, granite, gabbro and concrete. Twenty-five of each were randomly arranged horizontally 10–15 mm above the substrate at 4 m depth on each of two breakwaters and two rocky reefs in April 2007 (before May–October spawning season). After 12 months, tiles were brought to the laboratory, immersed in bleach for 24 h to remove organic matter, and juvenile corals on the bottom of each tile were counted. Twenty-five tiles went missing during the experiment.
Study and other actions testedA replicated study in 2010–2012 on five fringing reefs off St John, US Virgin Islands (Edmunds et al. 2014) found that the upper surfaces of unglazed terracotta or acrylic settlement tiles were colonized by stony corals when they had refuge holes, but not when they were smooth. No corals settled on upper surfaces of tiles without refuge holes during the study. On tiles deployed August 2010–June 2011 coral density did not differ between upper surfaces with refuge holes (0.97 corals/100 cm2) and lower surfaces (1.08 corals/100 cm2), but on tiles deployed June 2011–August 2012 there was lower density on upper surfaces with refuge holes (0.14 corals/100 cm2) than lower surfaces (1.31 corals/100 cm2). See paper for preferences of different coral species. At five sites off St John (<500 m apart), a cluster of 15 unglazed terracotta or acrylic settlement tiles was attached at 45° to horizontal at 5 m depth, 1 cm above the substrate, using stainless steel studs and a spacer which were attached to rocks with epoxy putty. Tiles were deployed August 2010–June 2011, then replaced and left until August 2012. When retrieved, tiles were cleaned, dried and inspected with a microscope for corals. For each sampling period, authors inspected the lower surface of seventy-five terracotta tiles (15 × 15 × 1 cm) and the upper surface of 20 terracotta tiles topped with acrylic tiles (15 × 15 × 0.6 cm) which had been drilled with holes on the top surface only, and 20 undrilled acrylic-only tiles.
Study and other actions testedA replicated study in 2010–2012 on three reefs off Lyudao, Lanyu and Kenting islands, Taiwan (Edmunds et al. 2014) found that the upper surfaces of unglazed terracotta or acrylic settlement tiles with refuge holes were colonized by a higher density of stony corals than upper tile surfaces with no holes. Four weeks after deployment, upper surfaces of tiles with refuge holes had a higher density of settled corals (1.6–7.9 corals/100 cm2) than upper surfaces without holes (0.3–1.9 corals/100 cm2) and lower surfaces (0.3–4.7 corals/100 cm2, data is not separated for lower surfaces with or without refuge holes). See paper for preferences of different coral species. Pairs of unglazed terracotta or acrylic tiles (10 × 10 × 1 cm) with a smooth and a grooved surface were stuck together, either with both grooved surfaces facing outwards (refuges) or both smooth surfaces facing outwards (smooth). Off three islands (70–105 km apart), 15–18 pairs of refuge and smooth tiles were fixed a few cm above the substrate at 45° to horizontal using stainless steel bolts at a depth of 5 m. Tile pairs were deployed in March–April (2–3 weeks before coral spawning), off Lyudao in 2010 and off Lyudao, Lanyu and Kenting in 2012, retrieved four weeks later, cleaned, dried and inspected with a microscope for corals.
Study and other actions testedA replicated study in 2010–2012 on three reefs off Caniogan, Cangaluyan and Lucero islands, Philippines (Edmunds et al. 2014) found that upper surfaces of fibre-cement settlement tiles with refuge holes were colonized by a higher density of stony corals than upper surfaces without holes. Five months after deployment, upper tile surfaces with refuge holes had a higher density of settled corals (1.9–11.4 corals/100 cm2) than smooth upper surfaces (0–1.7 corals/100 cm2) and lower surfaces (0.4–2.8 corals/100 cm2, data is not separated for lower surfaces with or without refuge holes). See paper for settlement surfaces of different coral species. Fifteen fibre-cement tiles (10 × 10 × 1.2 cm) with refuges (drilled with sixty-four 0.5 cm radius holes on each side) and 15 without refuges (smooth) were fixed 1 cm above the substrate at 45° to horizontal using concrete nails at a depth of 5 m on fore-reefs at Caniogan, Cangaluyan and Lucero (11–24 km apart). Refuge and smooth tiles were installed 30 cm apart in February 2012 and retrieved in July 2012. Peak coral spawning was March–May. Retrieved tiles were cleaned, dried and inspected with a microscope for corals.
Study and other actions testedA replicated, controlled study in 2007–2008 at two coral reefs at Glovers Reef and Carrie Bow Cay, Belize (Steneck et al. 2014), found that using exclusion devices on settlement tiles to deter herbivorous parrot fish led to a reduction in settlement by coral spat (settled larvae) and an increase in nuisance algae compared to tiles without devices. One year after exclusion devices were installed, the number of coral spat was lower on tiles with exclusion devices (0.3–0.6/tile) compared to tiles with just frames (1.3–1.5/tile) and bare tiles (0.9–1.7/tile). Coverage by nuisance macroalgae was also higher on tiles inside exclusion devices (38–68%) compared to tiles with wire (22–33%) and bare tiles (24–30%). Coral species were mainly Agaricia spp. and Porites spp. although there were no Porites spp. settled on any of the exclusion tiles. In March 2007, parrot-fish exclusion devices were placed around 24 terracotta settlement tiles (10 × 10 × 1 cm). Devices comprised a 20 cm diameter wire star-shaped frame with 15.2 cm vertical stainless-steel bolts attached at 4 cm intervals to resemble a ‘cage’. Frames only were attached to 24 tiles and a further 24 were left bare. Twenty-four groups of three tiles (one/treatment) were screwed to the substrate at each of Glovers Reef and Carrie Bow Cay. Coral settlement and algal growth were recorded after one year.
Study and other actions testedA replicated, paired study in 2008 at Iou Lukes reef, Palau (Edwards et al. 2015), found that settlement tiles allowed to ‘biologically condition’ for three months had a higher density of artificially enhanced or naturally settled stony coral spat (settled larvae) compared to tiles conditioned for one week, and density was higher on tiles with artificially enhanced coral larvae supply. One week or five weeks after nearby wild-growing stony coral spawned or larvae were artificially introduced to the tiles, density of coral spat was higher on tiles conditioned for three months (natural: 50; artificial: 205/0.1m2) compared to tiles conditioned for one week (natural: 4; artificial 29/0.1m2). Density was significantly higher on one-week conditioned and three-month conditioned tiles where larvae supply had been enhanced compared to the natural tiles. In January 2008 and April 2008, four fibre-cement settlement tiles (10 × 10 × 0.6 cm) were attached to each of 28 concrete/limestone ‘pallet-balls’ (1.2 × 0.9 m) placed 3–5 m apart, 5–8 m deep on the seafloor adjacent to a natural reef. Tiles were allowed to ‘condition’ (develop biofilm) for three months (January 2008) or one week (April 2008) before coral spawning. In April 2008, seven randomly selected pallet-balls were ‘seeded’ with nursery-cultivated stony coral Acropora digitata larvae (see paper for methods), and corals on the natural reef spawned. Tiles were retrieved either one or five weeks after wild-growing coral colonies had spawned and the number of coral spat was counted.
Study and other actions testedA replicated study in 2012–2015 at coral reef patches (‘microatolls’) off One Tree Island, Great Barrier Reef, Australia (Mallela et al. 2017) found that PVC pipes and the top of ceramic settlement tiles were colonized by a lower number of small stony coral recruits than the underside of ceramic tiles but there was no difference for larger coral colonies or overall coral cover. After 34 months, no coral recruits (<1 cm) were attached to PVC pipes or the top of ceramic tiles, compared to an average of 0.2 (range 0–2) on the underside of ceramic tiles. There was no difference in the average number of coral colonies (>1 cm) attached to PVC pipes (0.7, range 0–8) or the underside (0.6, range 0–7) or topside (0.2, range 0–3) of ceramic tiles. There was no difference in total coral cover (recruits and colonies) between settlement materials (data presented as a figure). In May 2012, thirty PVC pipes and 61 unglazed ceramic tiles were each fixed, horizontally, to a PVC frame attached to the substrate using cable ties. Ceramic tiles were placed in pairs with one tile facing upwards (30 tiles) and one facing down (31 tiles). PVC frames were placed randomly within three microtolls at 1–2 m deep. Corals were counted and measured in March 2015.
Study and other actions testedA replicated study in 2019 at a reef at Sir Abu Nu’Ayr Island off the United Arab Emirates (Bento et al. 2021) found that terracotta settlement tiles were naturally settled by stony corals (including Acropora spp. and Porites spp.). An average of three corals settled/tile, and all but two recruits settled on the grooved underside of the tiles. Acropora spp. made up 30% of settled corals, and Porites spp. made up 10%. In April 2019, thirty-one terracotta tiles (10 × 10 × 1 cm) were attached to the reef substrate (5 m deep, 2 m apart) using a screw and epoxy, with the grooved surface facing down. In September 2019, tiles were collected, and the number of recruits were counted, and species were identified.
Study and other actions tested
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This Action forms part of the Action Synopsis:
Coral ConservationRelated Actions
| Actions | Effectiveness | Studies | Category | |
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Repurpose obsolete offshore structures to act as structures for restoring coral reefs Action Link |
Awaiting assessment | 2 |
Synopsis Link |
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Use settlement tiles made from unnatural materials to encourage natural coral settlement Action Link |
Awaiting assessment | 16 |
Synopsis Link |
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Use structures made from unnatural materials to restore / repair / create habitat for corals to encourage natural coral settlement Action Link |
Awaiting assessment | 10 |
Synopsis Link |
Coral Conservation - Published 2024
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