Coral reefs have been in existence for millions of years; they are an intricate ecosystem and home to countless species of aquatic organisms. Their life is vital to the health and sustainability of the aquatic environment, which in turn directly influences our own well-being.

Unfortunately, these magical marine communities all over the world are under threat due to both local and global pressures such as overfishing, pollution, invasive species, changing weather patterns, physical impacts from ship groundings and storms, and worst of all, climate change. The world has lost 30 – 50 % of its coral reefs already. Without significant intervention, tropical reef ecosystems could face global extinction by the end of the century.

Why Do We Need Coral Reef Restoration?

Coral reefs today are under threat worldwide. It’s nothing new, but the degree to which corals die across the globe is alarming. The effect of current climate change, which directly impacts coral reefs due to the already observable increase in seawater temperature, was evidenced by the third global bleaching incident in 2016. The incident triggered a mass die-off of corals.

There are many methods and techniques for successful coral regeneration available to reef managers, many of which are very cheap and easy to build or preserve. But the research behind coral protection and regeneration is relatively recent, and these methods are continuously being developed. For community managers, each community or area will decide that different methods or techniques are more effective for them, and modification to techniques is important for local progress. It is necessary to bear in mind that errors are likely to be made in every new area, but they should not be replicated. 

The regeneration of degraded coral reefs may be assisted by a well-designed recovery strategy. However, it can only be effective if local causes of coral loss are tackled. More significantly, we need to reduce our greenhouse gas emissions to reduce ocean warming.

Types of Coral Restoration

Generally, there are two primary forms of restoration of coral known as active and passive restoration. Active coral restoration refers to programs that devote time, energy, money and other resources specifically to increasing the health, abundance or biodiversity of coral reefs. Increasing the health, abundance or biodiversity of coral reefs together comprise what is referred to as the coral reef resilience. A reef with a high abundance of healthy corals produced from a wide variety of coral genera is said to be robust or able to tolerate or rebound from disturbances. 

Ideally, active restoration takes place after passive restoration or the establishment of Marine Protected Areas (MPAs) has already been completed. The most common goals of active restoration are the conservation of degraded habitat and corals or the enhancement of reef stability to reduce potential disruptions. The hazard must first be minimized or removed in order to preserve the environment effectively. Yet, in many places around the world, the likelihood of preventing coral reefs from being lost by the huge array of threats is becoming less and less realistic. In such areas, scientists and conservationists instead aim to increase the reefs’ resilience to try to mitigate the degree of damage inflicted to hopefully maintain small patches of coral reefs, known as ‘biodiversity banks’. 

Application

Coral restoration may include growing asexually or sexually-derived corals in land-based or ocean nurseries for subsequent restoration, directly transplanting coral colonies or fragments from untouched areas (often under construction sites) to damaged reefs, and transplanting corals to substrate stabilization systems after ship grounding or dynamite fishing, respectively.

After being looked after and grown over time in the coral nursery, when corals have reached a certain size, they are usually planted out in the restoration area. Restoration approaches using asexually derived corals are somewhat invasive to the donor reef or individual donor corals. They do not encourage genetic diversity, as fragments are genetically similar to the donor colony, and they are the clones of their parents. Genetic diversity allows for mutations which may naturally increase a species diversity to threats. However, heterogeneity used in conservation projects can be a successful outreach method for the participation of local groups. It can be a valuable complement to sexual strategies, for example, coral species that spontaneously reproduce asexually and sexually (staghorn corals, some Acropora spp.).

The use of sexual coral reproduction for coral reef restoration involves experience and initial testing to establish the reproduction of a given species. This method can be adapted to all coral species, leaves natural habitats undamaged and leads to genetic diversity. This is particularly significant, since modern coral reefs have radically transformed their nature throughout the last few decades, and certain emerging genotypes may be better able to deal with these pressures than their currently deteriorating parents.

Up-scaling Restoration

Today, coral restoration remains costly and time-consuming and limited in scale. Each coral must be manually prepared and manually transplanted to the reef. It may not be possible to equal the rate at which reefs are disappearing worldwide, but the regeneration of reefs on a significant scale requires new approaches (restoration techniques urgently need to be upscaled). Key drawbacks to these approaches are the cost and labor implications. 

Future Implications

The elkhorn coral, and other key endangered species, which have trouble reproducing and coping with an evolving climate, could even be rehabilitated. But crucially, it is much better to protect what you have than to try to restore it from scratch!

We must bear in mind that the coral reef ecosystems that are suitable for rehabilitation may not become the reefs that they used to be. Coral conservation efforts may aim at restoring the ecological functionality of coral reefs, such as the habitat of diverse animals and plants and the preservation of biochemical cycles and the maintenance of economic services such as coastal protection, fisheries and tourism.

If local community leaders and conservationists can develop a well-thought-out restoration strategy, combined with larger scale restoration efforts, this could provide localized coral reefs with a chance to avoid extinction. If this can be combined with education, outreach and conservation, and strongly involving partners at projects on-site, this provides a glimmer of hope for coral reefs for the future.