Coral reef conservation and restoration

Coral reefs are marine ecosystems located in shallow coastal zones of tropical and subtropical regions. The ecosystem is shaped by the calcium carbonate structures secreted by the coral polyps (ref). Coral reefs occupy a small percentage of the world’s oceans, but they contain a disproportionately high share of its biodiversity (ref). 

Common on-site approaches to coral reef conservation and restoration

Common approaches for coral reef conservation include establishing protected areas or no-take zones that exclude anthropogenic disturbance of reef ecosystems. Conserving existing areas of coral reef often results in improved ecosystem service provision (ref). For coral reef restoration, rearing, transplanting and monitoring of coral reef fragments are possible approaches. The re-establishment of corals is very challenging. It may be possible to rear coral larvae on a large enough scale for coral reef restoration but experts, such as specially trained coral biologists, and possibly large facilities will be required (ref). 


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Coral reef conservation and restoration as an ecosystem-based adaptation (EBA) measure

The importance of coral reefs for a wide range of ecosystem services has been widely recognised, leading to conservation and restoration projects to maintain these services. Despite the potential adaptation benefits available from coral reefs, only a small number of restoration projects have been undertaken that focus on adaptation (ref). Nevertheless, coral reef conservation and restoration represent promising options for coastal adaptation.

Coral reefs provide coastal protection

Coral reefs can make an important contribution to the protection of shorelines from the destructive action of waves (ref), providing comparable wave attenuation benefits to artificial defences such as breakwaters (ref). Storm protection may become more important in a changing climate as sea levels rise and storm patterns change. However, the effectiveness of coral reefs as a form of coastal protection depends on many variables, such as reef crest profile, width and depth of the reef flat and surface roughness (ref). The value of coastal protection provided by existing coral reef ecosystems can be large; for example, in the Virgin Islands, it has been estimated as US$ 1.2 million per year (ref). Coastal protection of Bermuda’s coral reefs were estimated to be US$265.9 M per year (ref). In general, coastal protection values for coral reefs are difficult to calculate because of the uncertainty in the data.

Many coral reefs also support herbivorous grazers such as parrotfish, which produce sand that helps to replenish beaches and thus maintain beach profiles (ref). Sediment flow to beaches may become more important as sea levels rise and storm patterns in coastal areas exert pressure on dune and beach ecosystems (ref). 


© Peter Prokosch / grida.no 

Corals may keep pace with sea level rise

Under certain circumstances, coral reefs (along with mangroves and saltmarshes) can raise their surface elevation as sea levels rise, keeping pace with or even exceeding those rises being experienced (ref). This will depend on factors such as water quality and the absence of human stressors, but where accretion is possible the reefs are likely to be able to maintain their wave attenuation function.

Coral reefs serve as habitat and nursery grounds for fish, supporting fisheries and livelihoods

Coral reefs, together with adjacent mangrove and seagrass ecosystems, provide habitat in the form of food and shelter for many fish and marine invertebrate species that coastal human communities depend on for their livelihoods (ref). It is estimated that coral reefs produce 10 to 12% of the fish caught in tropical countries, and 20 to 25% of the fish caught by developing nations (ref). In the context of a changing climate, the continued provision of food and income from coral reefs could therefore play a significant role in maintaining people’s resilience and capacity to adapt.

Coral reefs support diversified livelihoods

Healthy coral reefs support a variety of different types of livelihoods: not just fishing, but also recreation and tourism industries (ref). Conserving and restoring coral reefs can therefore contribute to the maintenance of these livelihoods. Additionally, diverse livelihoods can increase people’s resilience to climate change; if climate change makes some livelihoods less reliable (e.g. due to declines in, or decreased predictability of, crop yields) access to a variety of other livelihood options can mean people and communities are less impacted. 

Additional benefits

There are benefits for biodiversity

Almost a third of the world’s marine fish species are found on coral reefs (ref). Restoring or conserving coral reefs may therefore have a positive impact on biodiversity.

Coral reefs contain species which are important for medicine

Many species found in coral reef ecosystems produce chemicals that are being used as sources of new medicines, including for cancer, arthritis, asthma, heart disease, ulcers, bacterial infections and other diseases (ref) and show potential for use in nutritional supplements, enzymes and cosmetics (ref).

Coral reefs can support tourism and recreation

The recreational value of reefs, as indicated by income from tourism, is potentially enormous (ref). For example, estimated reef recreation value in the Caribbean is approximately US$ 1,654 per hectare per year (ref). Maintaining healthy coral reef ecosystems for coastal protection can also protect tourism and recreation sectors.


© Glenn Edney / grida.no 

Coral reef restoration can be cost-effective

Depending on the circumstances, the restoration of coral reefs can be more cost-effective than building artificial structures. For example, an analysis of the economics of climate change adaptation across eight Caribbean nations (Anguilla, Cayman Islands, Antigua and Barbuda, Dominica, Barbados, Jamaica, Bermuda and St. Lucia) found that reef restoration was the most cost-effective approach in the majority of these nations (ref). Another study examined the costs of coral reef restoration versus tropical breakwaters and found that, on average, the costs of restoration projects were significantly cheaper than the costs of building tropical breakwaters (ref). The same study noted that if maintenance costs for breakwaters and other benefits of reefs (such as fisheries and recreation) were also considered the relative cost-effectiveness of coral reefs for coastal defence purposes would be likely to increase.  

Key issues that can affect success

Anthropogenic pressures

Almost three quarters of the world's coral reefs are thought to be deteriorating as a consequence of environmental stress (ref). Much of this pressure is anthropogenic, being a combination of terrestrial pressures (such as coastal urban development, pollution and nutrient enrichment), resource use pressures (such as mining and overfishing) and management activities (e.g. dredging). Together, they threaten the viability of coral reefs for wave energy attenuation, maintenance of fisheries and recreation (ref). It is important, therefore, that coral reef conservation and restoration focuses on mitigating and reducing these human-induced pressures.

Climate change pressures

Climate change is another challenge faced by coral reef ecosystems. Increasing sea temperatures and ocean acidification, when combined with anthropogenic pressures, are likely to result in losses of ecosystem function and services (ref) and coral bleaching, mortality and reduced ability to develop reef structure (ref). However, some coral ecosystems are already showing signs of recovery following bleaching events: a study by Graham et al. (2015) found that Indo-Pacific corals which were structurally complex and had a deep water depth were more likely to recover following such events. Coral reef conservation and restoration efforts as part of EBA need to consider the impacts of climate change. Restoration may therefore consider structural complexity and water depth of reefs, as well as reducing anthropogenic stresses.

Site and ecosystem characteristics

Of all reef components, the relatively high and narrow part of the reef, known as the ‘reef crest’, is the most critical component for wave attenuation benefits, as it is known to dissipate more than 80% of the total wave energy (ref). Therefore, reef conservation should prioritise protection of coral reef areas which include reef crests.  In addition to reef crests, reef flats also play a role in wave energy attenuation, dissipating about half of the remaining wave energy. The degree of wave energy reduction by the reef flat is dependent on its depth, particularly at the shallowest points, and bottom roughness (ref). Therefore, any reef degradation that increases water depth or reduces bottom roughness may reduce coastal protection benefits by increasing exposure to coastal erosion.

Maximum biophysical thresholds

Given that the effectiveness of coral reef wave attenuation is partly dependant on water depth, the coastal protection power of coral reefs is likely to be reduced during extreme weather events that raise water levels (for example, storm surges). However, the effectiveness of reef crests in reducing wave height is increased as the waves become stronger, indicating that reefs as a whole can still reduce risk during extreme events (ref), even if part of their attenuation power is lost.

Recovery after disturbance

Healthy reefs are able to recover or self-repair to a certain degree following environmental disturbances such as tropical cyclones or multi-year fluctuations in warm oceanic currents, which are responsible for mass bleaching and mortality. However, reefs which are under anthropogenic pressure do not generally recover well from such natural disturbance events (ref). This further emphasises the need for management practices that reduce levels of anthropogenic disturbance (e.g. high nutrient pollution and overfishing of herbivorous fish) on coral reefs and that work towards ensuring the resilience of these systems to climate change related impacts (ref).

Relevant policy context and developments

Creating an appropriate enabling environment, both in terms of the policy context and at the local level through a community-based emphasis, is needed for effective coral reef management. Coral reefs can be impacted by a range of pressures, including from outside sources such as terrestrial pollution, and many valuable reef seafood species also need adjacent ecosystems such as seagrasses and mangroves as a part of their life cycles (ref). Additionally, reef restoration can potentially impact on other groups (for example through potential reductions in diving activities to protect reef or restrictions to navigation routes and moorings to prevent boats damaging reefs). Therefore, it is especially important that the whole social and policy context is considered. Concepts such as integrated coastal (zone) management (IC(Z)M) and marine protected areas (MPAs) have received significant attention for their usefulness in this respect (ref). For more information on the importance of policy measures in adaptation, see our page on the importance of policy measures.

Ongoing management

Reef conservation and restoration activities depend on ecological processes that are time-demanding. As an indication, natural recovery of reefs after acute disturbances takes 5–10 years in the absence of chronic anthropogenic stressors (ref). Restoration projects should not expect to see results any sooner. Ongoing management of reef ecosystems is therefore key if they are to serve as a successful EBA measure. Effective management for resilience includes understanding EBA when planning, designing and implementing any management measure. Monitoring and using its results to adapt ongoing management is important. It will also require collaboration between a number of different types of stakeholders, including policy makers, scientists, environmental managers and local communities. For more information on effective coral reef management strategies, including management of local stressors, reducing land based impacts, managing for disturbance, and integrated approaches, see the Nature Conservancy's Coral Reef Module in the Useful resources and materials section at the bottom of this page. 

Restoration

Restoration of degraded coral reef ecosystems most commonly involves the rearing of coral fragments in coral nurseries, transplantation of these fragments to degraded reef areas, and subsequent management and monitoring to facilitate restoration. To date, most successful coral nurseries have been those which are located in mid-water, away from the natural reef, and where the fragments are free from predation (e.g. by corallivorous snails) and interference from divers (ref). Subsequent transplantation of coral fragments should ensure that the corals being transplanted are of the appropriate species and from a similar environmental setting, so that they are well adapted to survive at the restoration site (ref). These and other types of restoration activities need to take place alongside wider management efforts that address coastal land use patterns, water quality issues and fishing activities in order to improve ecosystem conditions. For more information on factors that determine on the ground reef restoration success, including good practice guidance, see Edwards (ed.) 2010 in the Useful resources and materials section at the bottom of this page. 

Useful resources and materials

  • The Nature Conservancy. An online module providing information, resources, and principles for how to select, design and manage coral reef protected areas for resilience to climate change. Includes module sections on management of local stressors, reducing land-based impacts, managing for disturbance, integrated approaches, monitoring and assessment, and a resources section providing links to useful resilience-related literature and tools. Coral Reef Module, Reef Resilience Toolkit
  • Edwards & Gomez. 2007. Coral Reef Targeted Research and Capacity Building for Management Program. A succinct yet comprehensive set of reef restoration planning and implementation guidelines for coastal managers, decision-makers and technical advisers involved in community based reef restoration efforts. The guidelines cover setting goals and success criteria for coral reef restoration projects; factors to consider in the physical and biological restoration of reefs; monitoring and maintenance of reefs; and costs of reef restoration projects. A final section presents lessons learned from five case studies, in locations ranging from the western Indian Ocean to French Polynesia. Reef Restoration: Concepts & Guidelines: Making sensible management choices in the face of uncertainty
  • Edwards (ed.). 2010. The Coral Reef Targeted Research and Capacity Building for Management Program. A manual complementing Edwards & Gomez (2007) “Reef Restoration: Concepts & Guidelines: Making sensible management choices in the face of uncertainty” with greater detail and hands-on advice, and based on lessons learned.  Includes detailed technical information on how to construct and manage nurseries to farm coral fragments, rear coral larvae and deploy coral transplants to degraded reef areas. Reef Rehabilitation manual
  • Marshall & Shuttenberg. 2006. Great Barrier Reef Marine Park Authority. A guide collating the latest scientific knowledge and management experience to help managers respond to mass coral bleaching events, including science-based suggestions for adaptive management. A Reef Manager’s Guide to Coral Bleaching
  • UNEP-WCMC. An online tool providing access to a range of datasets that are useful for informing decisions on conserving marine and coastal biodiversity. Users are able to view and download a range of data, including data on: the global distribution of coral reefs, seagrasses and mangroves; global seagrass species richness and data from the World Mangrove Atlas. Ocean data viewer
  • Japan Ministry of Environment. Collects the methods, achievements, and problems of measures including 1) seeding production and settlement induction by utilizing coral sexual reproduction, 2) transplantation of coral fragments by utilizing asexual reproduction, 3) transplantation of colonies or entire reef and 4) management of settled seeding, transplanted colonies and coral communities. Manual for Restoration and Remediation of Coral Reefs