Coral restoration is expensive and success can vary greatly between projects. Therefore, it is important to know whether restoration is the best strategy to use compared with other management actions (e.g., watershed restoration, MPA enforcement). Resources, funding, and capacity are often limited, so active restoration, including coral gardening, should only be utilized when there is a high chance of success over the long term.
Key questions to ask before starting a coral restoration project:
Did the site support a coral community prior to disturbance?
- Sites with historic populations of corals may be good candidate sites for restoration
- However, environmental conditions change so they no longer support healthy coral communities
What was the cause of disturbance or coral degradation?
- Determining the causes of coral degradation will help a manager decide whether these stressors will also negatively affect coral transplants
- If causes of degradation are related to global threats (e.g., high temperatures and bleaching driven by climate change), longer-term monitoring of the site may be needed to determine how often these stressors affect the site and whether it is a good candidate site for restoration
- If causes of decline in a site are unknown, a small-scale pilot study is advised that tracks coral transplant success over at least one year
Have the causes of degradation stopped or are they now under effective management?
- Areas where local stressors (e.g., land-based pollution or high levels of disease) continue to threaten corals should not be candidate sites for coral restoration, as transplants will have a low likelihood of success over the long-term
- At sites with high human impacts, effective forms of management need to be in place before active coral restoration is conducted, otherwise these active interventions have a high risk of failure and may be a waste of resources
- If local environmental conditions are poor (e.g., poor water quality from land-based nutrient pollution and sedimentation), the chances of establishing a sustainable coral population may be very low
- If macroalgae are highly abundant at a site because of low herbivore populations (e.g., due to overfishing), coral populations have little chance of recovering because macroalgae inhibit settlement of new corals
Could the site recover naturally from high coral recruitment?
- Is coral population recovery limited by low levels of natural coral recruitment because there is/are:
- few coral larvae in the water column
- low levels of coral settlement due to environmental factors such as high macroalgae
- high coral mortality after settlement
- Active coral propagation and transplantation may be particularly useful in sites where there are low levels of coral larvae, because coral gardening can boost population sizes of sexually-reproducing corals that will produce more coral larvae in the future. However, if recruitment is limited because of poor settlement or high mortality, other management actions will be needed before coral restoration should be implemented
- If natural coral recruitment is already high within a site, a restoration program may be unnecessary because the site may recover quickly on its own, thus limited resources could be used to support other management actions that support the health and functioning of the system
Does the substrate require stabilization?
- Stabilization of reef structure can potentially add substantial costs to a restoration project
- Recent advances, however, in technologies that combine coral gardening with structural enhancements are reducing these costs, though the long-term effectiveness of these structures requires additional research.
Carefully considering the costs required to run a coral restoration program is a critical step for ensuring a program’s long-term success. However, few resources exist that provide itemized cost estimates. Chapter 7 of the Reef Rehabilitation Manual is entirely dedicated to instructing managers on through cost-benefit analysis of coral restoration, and provides information on costs associated with details that may not be entirely obvious at the outset of a restoration project.
Costs associated with coral restoration can be broken down into the following six stages as suggested by the Reef Rehabilitation Manual:
- Collection of source material
- Setting up coral nursery/gardening facilities
- Establishing collected coral material in culture/nurseries
- Transplantation of corals to the restoration site
- Maintenance and monitoring of donor corals, nurseries, and outplanted corals
Going through the exercise of estimating these costs per coral transplant will help a manager or practitioner determine whether restoration is an efficient use of resources or whether resources would be better used on management activities that promote reef resilience.