Coral transplantation is one option available to managers considering rehabilitation of a degraded reef. Transplantation can be a cost-effective option for small scale rehabilitation efforts that do not divert funding from other coastal management priorities (e.g., repair of the reef at ship-grounding sites where there is funding available from damage compensation payments). The crucial prerequisite for coral transplantation is that any significant local anthropogenic impacts on the reef are under some form of effective management. Otherwise, there is a high risk that transplanted corals will not survive.
Transplantation may also be necessary, as a last resort, when decisions have been taken to proceed with a development project (e.g., port or other coastal construction, channel and harbor dredging, pipeline laying) that threatens reefs, such that corals will be killed unless moved to a safe location. In the United States, this is considered Compensatory Mitigation.
There are several components of the coral transplantation process to be considered:
Identification of Coral sources
Material for direct coral transplantation can be obtained through nurseries or from a natural reef where there are two main sources of transplants: ref
- “Corals of opportunity” which are fragments broken off from colonies by natural processes (e.g., storms) or human activity that can be found lying on the seabed. There may also be individual coral colonies that are at risk – badly bio-eroded or being overgrown (e.g., by algae or sponges, etc.). These corals can be “rescued” and either reared in nurseries prior to transplantation or directly transplanted to a restoration site.
- Donor colonies from which fragments can be obtained. Research suggests that as a precautionary measure, no more than 10% of a donor colony should be removed.
What Species to Transplant?
Careful selection of coral species to transplant is one of the most crucial steps in successful restoration. When considering which species to use, the most logical choice is one that occurs naturally at the rehabilitation site and is relatively common on nearby potential source reefs. Species that are known to have occurred naturally at the rehabilitation site in the recent past may also be considered. Fast-growing branching species may provide a rapid increase in coral cover and topographic complexity, but they tend to be more susceptible to bleaching, disease and coral predators.
Establishment of Nurseries
A prerequisite for reef restoration, at all but the smallest scale, is the establishment of coral nurseries that can supply large numbers (tens of thousands) of corals of a size that can survive and grow at the site to be rehabilitated.
Critical components to consider for a nursery include:
- Nursery design
- Substrates used for coral colony mariculture
- Realistic numbers and densities of colonies that can be maintained
- Duration of the nursery phase
- Growth rates and survival of farmed colonies
Several types of coral nurseries exist, varying in structure, size and purpose. The two major types are:
- Ex situ nurseries, which are located on land (expensive and largely for the specialist, such as those culturing corals to supply the aquarium trade)
- In situ nurseries that are located in the ocean
There is much to consider in nursery establishment and maintenance, beyond the scope of this Toolkit. Guidance can be obtained from the Reef Rehabilitation Manual which provides detailed information on:
- Site selection for a nursery
- Construction methodology for a nursery for asexual rearing of corals
- Issues to consider when stocking a nursery with corals
- Methods for maintenance of a nursery and corals
Method of Trans-plantation
Transplantation protocols need to be designed to reduce stress on the coral and to increase the success (i.e. coral survivorship) of the relocation efforts.
The method of transplantation that will be most effective in a given case will depend on the:
- Species of coral being transplanted
- Nature of the substrate at the transplantation site
- Environment at that site
Methods of transplantation vary for different environments, and several are described below.
Unattached and loosely attached transplants in sheltered environments
In some low-energy environments such as back-reef zones, lagoons and protected embayments, fragments of such species can survive and grow without being artificially attached to the substrate. In these limited situations, coral transplantation may be effective by the scattering of fragments of an appropriate species on the substratum. Fungiids (mushroom corals), several species of Acropora (including A. palmate and A. cervicornis in the Caribbean) and Porites, some species of Montipora and eastern Pacific Pocillopora damicornis have been reported to reproduce successfully by fragmentation, typically as a result of storm damage or by the actions of other reef organisms.
Attached without adhesives or cement in relatively sheltered environments
In relatively sheltered environments, smaller (< 10 cm) coral branches or fragments can be slotted into natural holes or crevices in the reef. Holes can also be created artificially using a hand-held auger, hand drill or compressed-air drill if the reef substrate is very hard. Larger fragments will generally require adhesives and even initial support wires for stability while waiting for self-attachment to occur. Such areas with natural holes at sheltered shallow sites are particularly suitable for community restoration projects.
Attachment with cement and epoxy adhesives
The use of adhesives and cement for fixing corals directly onto hard substrate is the most common transplantation method. The technique is labor-intensive; analysis of a range of studies suggest that only about 5–10 fragments or colonies can be attached per person-hour once all necessary peripheral activities are taken into account. The choice of adhesive depends on local availability, the environmental conditions at the restoration site, the size and morphology of the corals, the amount of coral that needs to be attached, and the manpower and financial resources available to undertake the restoration.
The following adhesives can be used for transplantation:
- Cement, usually in the form of sand-cement concrete, is cheaper than epoxy and may be the best choice for large massive and submassive corals and for repairing reef framework damaged by ship groundings or tsunamis.
- Ordinary Portland cement mixed with sand and freshwater (try to avoid using saltwater as this may interfere with the setting process and strength of the concrete) has been widely used, sometimes with admixtures to alter the rate of setting of the concrete. Type II Portland cement or specialist sulphate resistant marine cements with microsilica-based additives are recommended for use in the marine environment and can be used if available locally.
- Two-party epoxy putty (e.g., AquaMend, Epoxyclay Aqua) appear the easiest to use and most cost effective. Epoxy putty comes in small sticks (e.g., 60–70 grams) and the chemical reaction between the two parts does not begin until the two parts are mixed together. It has the advantage that for each transplant only the portion that is needed can be broken off from the stick.
Use of wire, fishing line and cable-ties
Insulated electrical wire, stainless steel wire, monofilament fishing line and cable-ties have all been used to attach coral transplants, usually either to artificial structures or to artificial substrates for nursery rearing (e.g. limestone slabs), which are later transferred to the reef once corals have grown. They may also be suitable for attaching fragments to thick dead coral branches or to nails or metal stakes fixed in the reef.
What Time of Year Should Transplantation Occur?
Times to avoid transplanting:
- Immediately before the stormy season
- When sea temperatures are highest, as bleaching is more likely and disease more prevalent
Aim to carry out transplantation during the coolest months in sheltered reef environments (e.g., within protected lagoons) where corals will be protected from storm waves, and prior to the calmest months in more exposed environments where water flushing will hopefully prevent corals from becoming heat stressed soon after transplantation.
See examples of coral transplantation projects in Florida and the Caribbean.
Monitoring and Maintenance
Monitoring of transplanted corals over time is an essential component of the restoration effort, providing an assessment of the viability and success of the project. Regular visual checks on the status of the transplants can help to identify problems that may require adaptive management (e.g., maintenance action to remove predators), whereas semi-annual or annual systematic surveys may be necessary to show progress toward longer-term objectives (such as increasing coral cover or reef fish biomass).
The parameters to measure during monitoring will depend on the aims and objectives of the project. The most common parameters measured are:
- Coral survivorship (i.e., whether dead or alive)
- Measurement of growth/loss of coral tissue
- Condition of structural attachment (i.e., has coral grown over epoxy? has coral shifted from where attached?)
- Qualitative description of coral health (e.g., notes on any pigment loss, bleaching, disease, evidence of predation, bio-fouling, breakage)
The following maintenance activities should be considered as part of the monitoring process:
- Reattachment of detached transplants. Depending on the method of transplantation used and the amount of care taken, some corals may become detached as a result of physical disturbance (e.g., waves, fish, divers)
- Removal of loose fouling materials, whether in the form of man-made flotsam (e.g., garbage, fishing net) or natural items like loose seaweed fronds
- Removal of coral predators such as some gastropods (e.g., Drupella, Coralliophila) and some echinoderms (e.g., Acanthaster, Culcita)
- Removal of fouling organisms, notably fleshy or filamentous macroalgae, sponges and tunicates that may overgrow transplants