Below are three factors that help you determine which (if any) areas to restore: 1) the ecological history of a site; 2) the biological and physical characteristics of a site; and 3) the feasibility for restoration.
Can a previous coral community or “reference site” be identified?
Select sites where there’s evidence that the coral species being restored once thrived
- In some cases, your site may be degraded and it is not possible to determine what natural coral communities in the site looked like, which coral species should be reestablished, or what coral densities are best. In such cases, you should identify a “reference” site or community near the potential restoration location.
- Selecting a reference site can help to determine whether the environmental conditions in that site have changed such that the coral species or community will no longer thrive.
- If a reference site or community nearby cannot be located, this could be a sign that restoration may not be successful in that area due to poor environmental conditions, and should call into question the feasibility of restoration due to potential difficulties finding source corals.
What sites are suitable for restoration?
- If the primary reason for restoration is to enhance a population of a particular coral species, then selecting for indicators that suggest a good environment for this population will be important.
- If the primary reason for restoration is to enhance ecosystem services, such as fisheries, then other environmental conditions, sites, or methods may be more valuable and affect which sites will work best.
- Projects aimed at restoring coral reefs to enhance coastal protection can use the Atlas of Ocean Wealth, which shows areas that are likely to have a higher impact for increasing coastal protection.
- For outplanting activities, managers should locate sites that have conditions that support healthy coral communities and may be more resilient to stressful events like warm sea surface temperatures. Prior to starting restoration, a “fact-finding” exercise can be undertaken to compare potential sites and their environmental or ecological quality. The following indicators are often used to evaluate the resilience of sites:
- Existing wild populations – reefs where the coral species being outplanted currently or have historically thrived can be good candidates for a reef site. However, the causes of degradation and decline for that species should be removed before restoration begins. Surveys should be done of existing corals to determine their level of environmental stress, predation, bleaching, disease, and algal overgrowth before outplanting occurs.
- Origin of parent colonies – if nursery corals were raised from donor colonies, it may be helpful to match the environmental conditions of the outplanted coral’s parent colonies or to the conditions of the nursery site to enhance overall survivorship.
- Site depth – depths at which corals will be transplanted should be similar to the depths where the coral species normally grows. This can be determined by finding the depths of donor colonies or by surveying wild colonies of the coral species on other reef sites.
- Bottom type – areas with loose rubble or materials, as well as excessive sand, fine-grained sand, and turf algae that binds to sediment should be avoided.
- Water quality – sites should have good water quality, such as good light penetration and low levels of sediment and nutrients. Areas near watershed discharge sites should be avoided.
- Biological stressors – areas with high coral predator abundance (such as snails or sea stars), damselfish territories on corals, or high levels of competition between corals and other benthic space competitors (e.g., algae, sponges, gorgonians, fire corals) should be avoided.
- Site accessibility – it is important that outplant sites be easily accessible and can be located after outplanting so that monitoring can be conducted.
- Protected status – outplant sites should be in areas with reduced levels of human activities that can cause damage to outplants. Conducting outplanting within MPAs or in areas that are less visited by tourists or fishermen can reduce potential damage and increase outplant survivorship.
- Overall reef site resilience and health – general reef surveys should be conducted to ensure high overall health of the outplant site. The Nature Conservancy has developed evaluation criteria to rate the overall ecological health of potential outplant sites by surveying several different resilience factors. This survey is based on a modified version of the AGRRA. All factors for a site are added together, and sites that rank highest are targeted for outplanting efforts. So far, better outplant survivorship has been recorded at sites that had higher resilience scores based on this system.
The Nature Conservancy evaluation criteria for selecting outplanting sites. Credit: Kemit Amon-Lewis, TNC.
|Criteria||Measure||Score: 1||Score: 2||Score: 3|
|Water quality||Local area knowledge||No issues||Moderate issues; typically after rain events||Known issues and point sources of discharge|
|Flow||Local area knowledge||Constant flow||Moderate flow||Lagoonal; sometimes still|
|Acroporids||Measured abundance||>50 colonies||25-50 colonies||<25 colonies|
|Coral assemblage||Measured % cover and diversity||>20% coverage and >50% coral genera||>20% coverage or >50% coral genera||<20% coverage and <50% coral genera|
|Damselfish||Measured % predation mark per colony||<5%||5-15%||>15%|
|Macroalgae||Measured % coverage||1-5%||6-10%||>10%|
|Health||Measured % bleaching and paling||0%||1-20%||>20%|
Size of transplantation area, coral species, and source of transplants?
To determine whether a site is feasible for restoration, a fact-finding mission is advised, taking into consideration the following points:
- The extent of the areas requiring outplanting: As the cost of transplantation will be proportional to the restoration area, measure the total area where transplantation will occur. Consider costs and whether you will be able to achieve the scope and scale of the restoration project for it to be successful.
- Which coral species are appropriate for outplanting: Most restoration programs work with branching species (like acroporids and pocilloporids) because they are fast-growing and generate important habitat for small fish and invertebrates. However, these corals may be more vulnerable to bleaching and storm impacts. Thus, boulder species are also important because they build reef structure and are often more tolerant of stressors than branching corals. A broad range of coral species and types should be considered for restoration to minimize risk.
- Local sources of coral fragments for nurseries and outplanting: Proximity of the donor sites, nursery location, and restoration sites for outplanting are important considerations. You also need to determine whether a coral nursery is required versus simply taking source corals or “corals of opportunity” (natural fragments on the reef that have a poor chance of survival). Source sites should be no more than 30-60 minutes away by boat to minimize stress and loss of coral fragments. More information on this is provided in the Asexual Propagation Collection page.