Action

Stabilize damaged or broken coral reef substrate or remove unconsolidated rubble

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Six studies examined the effects of stabilizing damaged or broken coral reef substrate or removing unconsolidated rubble on coral colonies. Three studies were in Indonesia, and one was in each of the Maldives, the Phillipines and Puerto Rico5.

COMMUNITY RESPONSE (0 STUDIES)

POPULATION RESPONSE (4 STUDIES)

  • Abundance/Cover (5 studies): Five studies (three replicated, including two controlled) in the Maldives, Indonesia, and the Philippines reported that in areas where degraded coral reefs were stabilized, coral numbers and coverage increased compared to those with unstablized coral rubble. One of the studies found that coral numbers and coverage varied between reefs stabilized with rock piles compared to other materials, another study found density varied with different configurations of rock piles and one study found more corals on structures designed to provide a high level of stability.
  • Survival (1 studies): One controlled study in the Philippines found that on areas where coral reef was stabilized stony coral survived and survival was higher than in unstabilized areas.
  • Condition (1 study): A study in Puerto Rico reported that stabilizing a patch of damaged coral reef, as well as transplanting wild-grown and nursery-grown fragments of staghorn coral, led to the patch of restored reef more than doubling in size, whereas no growth was reported on an unstabilized patch.

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

  1. A study in 1990–1993 at an area of degraded coral reef in Galu Falhu, Maldives (Clark & Edwards 1999) reported that using artificial structures to provide greater stability to coral rubble substrate led to an increase in the number of coral colonies. After 3.5 years, approximately 500 coral colonies (average density 13/m2) were recorded on structurally complex concrete/PVC blocks that provided high substrate stability. After 3.5 years, average density on concrete mats that provided medium stability was 3 recruits/m2 but 18/m2 on the edges. After 3.5 years, some corals were observed attached to chain link fencing designed to provide low stability (numbers not reported). After 2.5 years, coral coverage on the unstabilized rubble had declined from 0.8% to 0.19%. In 1990–1991, four 10 × 5 m areas of previously mined coral rubble substrate at four sites each received one of three artificial substrate-stabilizing structures or were left unstabilized. Structures comprised complex concrete/PVC blocks (providing high stability), concrete mats (medium stability), or chain-link fencing (low stability) (see paper for design). Structures were deployed 0.5–1.8 m deep and were either sufficiently heavy to prevent movement by wave action or, for the concrete mats and chain-link fencing, weighted down using paving slabs. Monitoring took place at 8–12-month intervals for 2.5–3.5 years. Costs (presented in 1999): concrete/PVC blocks £210/m2; concrete mats £66/m2; chain-link fencing £26/m2.

    Study and other actions tested
  2. A replicated study in 2000 at a degraded coral reef in Komodo National Park, eastern Indonesia (Fox & Pet 2001) reported that stabilizing damaged coral substrate using piles of quarried rocks led to an increase in stony coral numbers compared to unstabilized coral rubble. Results were not tested for statistical significance. After six months, stony coral numbers on the stabilized reef ranged from 1-20/m2 and after 12 months 1-36/m2 compared to no observed increase in coral numbers on the unstabilized areas (data not reported). In April 2000, three or more 0.5–2.0 m3 rock piles were installed at each of nine sites with coral-rubble substrate (comprising dead coral fragments) across Komodo National Park. Sites were surveyed for stony coral recruits in October 2000 and April 2001 using six 1 m2 quadrats/site. Costs: US$ 5–10/m2 (reported in 2001). 

    Study and other actions tested
  3. A replicated, controlled study in 1998–2001 at nine coral rubble sites in the Komodo National Park, Indonesia (Fox et al. 2005) found that stabilizing coral rubble using piles of rocks led to a higher number and coverage of coral recruits compared to rubble stabilized using cement blocks, or netting, or unstabilized rubble. After three years, the average number of corals was highest on rock piles (13/plot) followed by cement blocks (11/plot) and netting (7/plot) and lowest on unstabilized rubble (5/plot). Average area (cm2/plot) covered by coral recruits was highest on rock piles (476 cm2), followed by cement blocks (270 cm2), and netting (253 cm2), and lowest on unstabilized rubble (188 cm2). In October and November 1998, two–four 1m2 plots were placed at each site with either rock piles (20–40 cm high, rocks 20–30 cm diameter), cement blocks, or netting (~5 cm mesh) pinned to the substrate. An additional four plots/site were left as unstabilized rubble. The number of coral recruits and area covered was recorded every six months for three years. Plots began to degrade after 2.5 years due to strong currents.

    Study and other actions tested
  4. A controlled study in 2003–2006 on a platform/patch coral reef in Negros Oriental, Philippines (Raymundo et al. 2007) found that in plots where rubble was stabilized with plastic mesh carpets and stone piles, new stony corals settled and had greater survival and cover than corals on unstabilized rubble. On stabilized plots established in the spawning season, corals settled within three months and reached 1–8 individuals/m2 after 36 months. On plots established after spawning, they settled within a year and reached 4–7 individuals/m2 after 32 months. Over a 10-month period after settlement, coral survival and colony size was greater on stabilized plots (survival: 63%, diameter: 6 cm) than unstabilized rubble (survival: 6%, diameter: 2–4 cm). Two years after establishment, stabilized plots had a higher average coverage of corals (19%) than unstabilized rubble (8%), but lower than adjacent healthy reef (44%). Five 17.5 m2 plots were established, three in June 2003 (coral spawning season) and two in October 2003 (before storm season). Plots were at the edge of a 2,400 m2 rubble field created by dynamite fishing, within a platform/patch reef in the Calagcalag Marine Protected Area. In the plots and the areas in between, plastic mesh carpets (2 cm mesh) were anchored to the rubble with metal stakes (with holes cut to accommodate existing coral), and rock piles (1 pile/0.5 m2, 1 m high) were placed on top of the mesh. Corals in plots and in transects through untreated rubble and adjacent healthy reef were counted 1–4 times/year for three years. In May 2004, ten to twelve coral recruits from each plot established in June 2003 (total 30 recruits) and 25 recruits from the rubble field were tagged and monitored for growth and survival for 10 months.

    Study and other actions tested
  5. A study in 2006–2014 at a damaged coral reef site in Tallaboa, Puerto Rico (Raymundo et al. 2015) reported that stabilizing the substrate along with transplanting wild-grown and nursery-grown fragments of staghorn coral Acropora cervicornis, led to the area of restored reef increasing. After eight years, the area of restored reef had grown from 70 m2 to 180 m2. Coral colonies in unrestored areas in the vicinity, with loose rubble and damaged substrate, showed no signs of recovery during the same period. It was not possible to determine from the study how much of the recovery was attributable to stabilizing the substrate, transplanting loose fragments, or transplanting nursery-grown fragments. In 2006, following the destruction of a coral reef by a ship grounding, wire cages and metal stakes were used to stabilize a 70 m2 area of damaged reef. Approximately 227 (10-20 cm) loose fragments of staghorn coral were collected from nearby reefs and attached to the substrate using cement puddles. In 2009–2011, approximately 400 (20–40 cm) fragments of staghorn coral were collected from a nursery and attached to the substrate using masonry nails, cable ties and/or epoxy. Coral recovery was measured using aerial imagery in 2014. No other methods are reported.

    Study and other actions tested
  6. A replicated, controlled, before-and-after study in 2002–2016 at four sites in Komodo National Park, eastern Indonesia (Fox et al. 2019) found that using piles of quarried rocks to stabilize coral rubble substrate resulted in an increase in coral density compared to unstabilized rubble, and coral cover varied on different rock configurations. Average stony coral cover on the rock piles increased over time and reached 45% after 14 years compared to 3% on the adjacent unstabilized coral rubble site. Coral cover varied between rock configurations (range: single rock: 3—68%; small piles: 20—61%; parallel: 24—83%; perpendicular: 39—68%). In 2002, over 6,000 m2 of quarried rock (20–30 cm diameter) was placed 6–10 m deep at four sites within the Komodo National Park (Gillawadarat, Karang Makassar, Padar, and Papagarang). Rocks were placed in different configurations: single rock pile; small piles 1–2 m3; parallel to the prevailing current; and perpendicular to the prevailing current. Rock piles were surveyed in 2004, 2008 and 2016 using five–eight 1 m2 quadrats that the authors selectively placed to capture the range and type of cover.

    Study and other actions tested
Please cite as:

Thornton A., Morgan, W.H., Bladon E.K., Smith R.K. & Sutherland W.J. (2024) Coral Conservation: Global evidence for the effects of actions. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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Coral Conservation

This Action forms part of the Action Synopsis:

Coral Conservation
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Coral Conservation - Published 2024

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