How is coral restoration going? — Part 2: Problems and future considerations

Written by Sara Gagliardi

Edited by Evan Quinter

In my last month’s publication (read here), we talked about the importance of coral restoration as a conservation tool to preserve coral reefs and the methods that exist to restore reefs throughout the world. Today, I am going to show the problems and difficulties Boström-Einarsson and colleagues highlighted for coral restoration, as well as the solutions they provided to face such obstacles. Critics of coral restoration include the definitions of restoration, the statement of objectives, the confusion in the scientific publications and sometimes the publication of inadequate methods.

Defining restoration

The term restoration has been defined for the terrestrial field by the Society for Ecological Restoration International Science & Policy Working Group as “the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed.” Further, “restoration attempts to return an ecosystem to its historic trajectory”. Hence a restored ecosystem “contains sufficient biotic and abiotic resources to continue its development without further assistance or subsidy”. However, for coral reefs both restoration and rehabilitation (i.e., the reparation of ecosystem processes, productivity and services) are included in the term “restoration”, which leads to confusion in the scientific community. Indeed, since the field of ecological restoration has been mainly developed in terrestrial ecosystems, its definition is disconnected from the field of coral restoration. For example, the recovery of endangered species, such as Acropora sp., does not fit the ecological component.

Fig. 1: Coral nursery from the Coral Restoration Foundation.

A problem of communication and claiming the objectives

A major problem regarding coral reef restoration is the lack of communication and collaboration between practitioners, managers and scientists. Many methods and project outcomes, especially failures, have not been documented in the scientific literature, avoiding the progress of research and increasing the risk of repeatedly testing similar methods. Researchers and practitioners should be more explicit when describing the metrics calculated, avoid inventing new ones or using complex equations, and should better communicate their observations and discoveries.

Furthermore, objectives are often unclear and difficult to achieve. Many projects with an ecological objective of restoring coral reefs (e.g., accelerating reef recovery, re-establishing a functioning reef ecosystem, or mitigating population declines and endangered species management) are often not measuring what they aim to. For example, many projects with this ecological objective only measured outcomes related to the growth and survival of individual corals. Even though these biological metrics (survival, growth, etc.) are important to assess the feasibility of coral restoration, the monitoring of ecological patterns is key for evaluating the achievement of the objectives. However, as most projects monitor the success over 12 months, many ecological patterns linked to coral reproduction cannot be measured, as coral fragments need more time to reach reproductive maturity.

Assessing the success of restoration

Five main obstacles have been identified to hinder the scaling of ecological restoration. First, most designs were poor and did not align with the objectives of the restoration project, hence inflating the success. For example, many projects were found to lack experimental controls and replication, or had an inadequate reference system, etc. Second, most peer-reviewed projects identified by Boström-Einarsson and colleagues were carried out on a short temporal scale (12 months on average). Consequently, the growth and survival rate, common measures for evaluating the outcome of restoration, can be inflated because of a mismatch between the relatively short monitoring times and the temporal scale at which disturbances occur, as bleaching events, destructive storms, or disease outbreaks, can affect the restored area after the survey has been completed. And because the mortality of corals tends to be higher in the early life stages of corals, this might further affect the outcomes of the restoration success.

Moreover, the lack of suitable and constant monitoring, and the scarce reports on the progress and outcomes of restoration projects makes it difficult to assess whether the restoration projects are successful on a long-term scale. As for many projects it is difficult to increase the spatial and temporal scale, because of financial as well as structural and logistic problems, many researchers are afraid the success of restoration is exaggerated due to these biases. Finally, even though the survival rate of restored coral was found to reach 66% on average, differences linked to the coral genera and environment were found. It is therefore important to consider all biotic and abiotic factors while assessing the success of restoration projects.

Fig. 2: Coral transplantation (Coral Restoration Foundation).

A fundamental critic

Critics argue the efforts on restoring coral reefs (local management) is inefficient to face the degradation of these ecosystems if they are not coupled with projects aiming in mitigating climate change and other threats (e.g., water quality decline, fishery, physical destruction) at the ecosystem scale. Coral restoration is key for the short-term protection of reef biodiversity and necessary to protect and recover endangered and rare coral species (e.g. Acropora palmata and A. cervicornis in the Caribbean), and might serve as a bridge to allow large-scale climate actions to be established and enable coral recovery. Finally, coral restoration programs allow the local populations to increase their interest and stewardship in protecting coral reefs.


Providing a systematic review of current methods, highlighting common problems and areas of concern, and identifying knowledge gaps is a key step for allowing the progress on the research of coral restoration and the conservation of coral reef ecosystems. To reach out on the problems cited before and provide a clear recapitulation of the current global restoration approaches, Boström-Einarsson and colleagues have combined three tools (review, database, and visualization). These will improve the success of restoration projects on coral reefs, as well as inform researchers on the directions that should be followed. Moreover, they suggest clear realistic objectives that are specific, measurable, achievable, realistic, and time-bound (SMART).


Boström-Einarsson L, Babcock RC, Bayraktarov E, Ceccarelli D, Cook N, Ferse SCA, Hancock B, Harrison P, Hein M, Shaver E, Smith A, Suggett D, Stewart-Sinclair PJ, Vardi T, McLeod IM. 2020. Coral restoration – A systematic review of current methods, successes, failures and future directions. PLOS ONE 15:e0226631.

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