Coral restoration in a changing world - a global synthesis of methods and techniques

Boström‐Einarsson, Lisa, Ceccarelli, Daniela, Babcock, Russell C., Bayraktarov, Elisa, Cook, Nathan, Harrison, Peter, Hein, Margaux, Shaver, Elizabeth, Smith, Adam, Stewart-Sinclair, Phoebe J., Vardi, Tali, and McLeod, Ian M. (2018) Coral restoration in a changing world - a global synthesis of methods and techniques. Report. Reef and Rainforest Research Centre Ltd, Cairns.

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Coral reef ecosystems have suffered an unprecedented loss of habitat-forming hard corals in recent decades, due to increased nutrient outputs from agriculture, elevated levels of suspended sediment caused by deforestation and development, destructive fishing practices, over-harvesting of reef species, outbreaks of corallivorous crown-of-thorns starfish (COTS, Acanthaster planci), coral disease and tropical storms. However, in recent years climate change has emerged as the primary threat to coral reefs. While reefs have a natural capacity for recovery, recurring events like mass coral bleaching and extreme weather events is increasing in frequency, intensity and severity, and are eroding the time for recovery between catastrophic events.

Marine conservation has primarily focused on passive habitat protection over active restoration, in contrast to terrestrial ecosystems where active restoration is common practice. Further, active restoration is well accepted for wetlands and shellfish reefs however coral reef restoration has remained controversial both in academia and amongst marine managers. This is despite recent research suggesting that optimal conservation outcomes include both habitat protection and restoration. Critics often argue that coral restoration detracts focus from mitigating climate change and other threats to the marine environment, while proponents of coral restoration counter that interventions can serve to protect coral biodiversity and endangered species in the short-term, while mitigation of large-scale threats such as climate change and water quality take effect. Despite this disconnect between coral restoration practitioners, coral reef managers and scientists, active coral restoration is increasingly used as a tool to attempt to restore coral populations.

The field has largely developed through independent work of isolated groups, and has fallen victim to ‘growing pains’ associated with ecological restoration in many other ecosystems. Partly this is due to a reluctance to share outcomes of projects, and in some cases a lack of monitoring or appropriate reporting of project outcomes. To mitigate this, we aimed to synthesise the available knowledge in a comprehensive global review of coral restoration methods, incorporating data from a traditional literature search of the scientific literature, complemented with information gathered from online sources and through a survey of coral restoration practitioners.

We identified 329 case studies on coral restoration, of which 195 were from the scientific literature, 79 were sourced from the grey literature (i.e. reports and online descriptions), and 55 were responses to our survey of restoration practitioners. We identified ten coral restoration intervention types: coral gardening - transplantation phase (23% of records), direct transplantation (21%), artificial reefs (19%), coral gardening - nursery phase (17%), coral gardening (both phases, 7%), substrate enhancement with electricity (4%), substrate stabilisation (4%), algae removal (2%), larval enhancement (1%) and microfragmentation (<1%). The majority of interventions involve coral fragmentation or transplantation of coral fragments (70%). While 52 countries are represented in the dataset, the majority of projects were conducted in the USA, Philippines, Thailand and Indonesia (together representing 40% of projects).

Coral restoration case studies are dominated by short-term projects, with 66% of all projects reporting less than 18 months of monitoring of the restored sites. Overall, the median length of projects was 12 months. Similarly, most projects are relatively small in spatial scale, with a median size of restored area of 500 m2. A diverse range of species are represented in the dataset, with 221 different species from 89 coral genera. Overall, coral restoration projects focused primarily (65% of studies) on fast-growing branching corals. Among all the published documents, the top five species (22% of studies) were Acropora cervicornis, Pocillopora damicornis, Stylophora pistillata, Porites cylindrica and Acropora palmata. Over a quarter of projects (26%) involved the coral genus Acropora, while 9% of studies included a single species - Acropora cervicornis. Much of the focus on Acropora cervicornis and Acropora palmata is likely to have resulted from these important reef-forming species being listed as threatened on the United States Endangered Species List and as Endangered on the International Union for Conservation of Nature Red List of Endangered Species (IUCN 2018).

We have dedicated a section to each intervention type covered in this review, and describe the potential and limitations of each intervention type in detail there. However, collating this information has highlighted the following main points which apply to coral restoration in general.

1. On average, survival in restored corals is relatively high. All coral genera with sufficient replication from which to draw conclusions (>10 studies listing that genus) report an average survival between 60-70%.

2. Differences in survival and growth are largely species and/or location specific, so the selection of specific methods should be tailored to the local conditions, costs, availability of materials, and to the specific objectives of each project.

3. Projects are overall small and short, however substantial scaling up is required for restoration to be a useful tool in supporting the persistence of reefs in the future. While there is ample evidence detailing how to successfully grow corals at smaller scales, few interventions demonstrate a capacity to be scaled up much beyond one hectare. Notable exceptions include methods which propagate sexually derived coral larvae.

4. To date, coral restoration has been plagued by the same common problems as ecological restoration in other ecosystems. Mitigating these will be crucial to successfully scale up projects, and to retain public trust in restoration as a tool for resilience based management.

a. Lack of clear objectives - There is a clear mismatch between the stated objectives of projects, and the design of projects and monitoring of outcomes. Poorly articulated or overinflated objectives risk alienating the general public and scientists, by over-promising and under-delivering. Social and economic objectives have inherent value and do not need to be disguised with ecological objectives.

b. Lack of appropriate monitoring - A large proportion of projects do not monitor metrics relevant to their stated objectives, or do not continue monitoring for long enough to provide meaningful estimates of success. Further, there is a clear need for standardisation in the metrics that are used, to allow comparisons between projects.

c. Lack of appropriate reporting - The outcomes of a large proportion of projects are not documented, which restricts knowledge-sharing and adaptive learning.

While we attempted to access some of the unreported projects through our survey, it is clear we have only scratched the surface of existing knowledge.

d. Poorly designed projects - An effect of inadequate monitoring and reporting is that projects are poorly suited to their specific area and conditions. Improved knowledge-sharing and development of best practice coral restoration guidelines aims to mitigate this problem.

Item ID: 59790
Item Type: Report (Report)
ISBN: 978-1-925514-31-5
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Copyright Information: © James Cook University 2018 Creative Commons Attribution Coral Restoration in a changing world - A global synthesis of methods and techniques is licensed by James Cook University for use under a Creative Commons Attribution 4.0 Australia licence. For licence conditions see:
Additional Information:

NESP Project 4.3 Technical report

Funders: NESP Tropical Water Quality Hub
Projects and Grants: NESP Project 4.3
Date Deposited: 13 Aug 2019 01:15
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 50%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050207 Environmental Rehabilitation (excl Bioremediation) @ 50%
SEO Codes: 96 ENVIRONMENT > 9612 Rehabilitation of Degraded Environments > 961201 Rehabilitation of Degraded Coastal and Estuarine Environments @ 50%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
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