Although restoration can be expensive, and likely to be effective in only very limited circumstances, there are situations where restoration can play an important role in assisting coral reefs to recover from damage. Where chronic stressors (such as pollution) have contributed to reef degradation, active restoration methods are unlikely to meet expectations.
The primary aim of coral restoration is to improve a degraded reef in terms of ecosystem structure and function. Other attributes of the system that may be considered are biodiversity, complexity, species biomass and productivity. Restoration is often driven by economic, legal, social and political considerations. These can be valid drivers for active restoration, but in these cases, it is important to have clear and realistic aims and to not ignore ecological realities.
Key considerations for coral reef restoration include:
- Coral reefs that are relatively unstressed by anthropogenic impacts can often recover naturally from disturbances without human intervention.
- Active restoration is not a magic bullet. Improved management of reef areas is the key.
- Active coral reef restoration has been carried out with some success at scales of up to a few hectares only.
- At small scales where a reef has been damaged through physical impacts from human activities restoration is more likely justifiable.
- Consider restoration as an ongoing process over a time-scale of years which is likely to need adaptive management, not as a one-off event.
- Targets or measurable indicators should be set that allow both the progress towards restoration goals to be assessed over time and adaptive management of the restoration project.
For detailed guidance on the issues, methods and limitations associated with ecological restoration of coral reefs, managers are referred to the comprehensive guidance prepared under the GEF Coral Reef Targeted Research program: Reef Restoration Concepts & Guidelines and Reef Rehabilitation Manual. A brief overview of information discussed in these guidance documents is provided below.
There are two main types of physical restoration:
- Repair of damaged reefs — In cases where acute impacts have cracked coral boulders, overturned massive corals, dislodged and fragmented coral colonies and other sessile organisms, or deposited foreign objects on the reef, emergency restoration in the short term can greatly assist recovery. This may involve applying cement or epoxy to large cracks in the reef framework, or righting and reattaching corals, sponges and other reef organisms.
- Artificial reef creation — The use of artificial reefs is within the scope of physical restoration. These may range from limestone boulders, to designed concrete or ceramic modules, to minerals (brucite and aragonite) electrolytically deposited on shaped wire mesh templates.
Active restoration may also be warranted at larger scales where there is a need to accelerate biological processes of recovery, such as when there is widespread depletion of a population. The decline of Acropora populations in areas of the Caribbean due to disease is an example of large scale impact that has warranted development and testing of coral propagation and outplanting as ecological restoration strategies. These strategies have generally aimed to increase the density of reproductive individuals to assist natural recovery processes, rather than attempting to rebuild coral communities through direct transplantation.
Restoration can also be implemented to reinstate key ecological functions to a damaged reef. An example of this use of restoration is the enhancement of sea urchin populations to support algal control efforts in areas where seaweeds are preventing coral recovery.
One example of an attempt at ecosystem restoration is the Maunalua Bay Reef Restoration Project which resulted in the removal of over 3 million pounds of Avrainvillea amadelpha (leather mudweed), an invasive alien alga from coral reef habitat in Maunalua Bay, located in southeast O‘ahu, Hawai‘i. Community volunteers alone removed 91,500 pounds of algae. All invasive alien algae were turned to productive use as a fertilizer on local farms. A Community Monitoring Protocol was established in partnership with The Nature Conservancy scientists to monitor the 27 acres that have been cleared. This project is the first critical step to restoring coral reef and seagrass systems in Maunalua Bay.