These restoration techniques aid in reducing further damage after its initial cause and enhance the natural recruitment process. Most if not all restoration projects have included some form of reef repair in their framework.
Coral Growth Assessment on an Established Artificial Reef in Antigua
As mentioned above triage is a key practice in reef repair. This is a term that involves a variety of restoration activities that all revolve around the stabilization and return to the needs of the current reef environment. Vessel salvage will usually include removing objects from deck to increase buoyancy and make removal easier. The stabilization and removal of rubble and debris is imperative to a reef community because storms can easily create a resuspension of these particles seriously affecting the environment. Lift bags, lift vacuums, clam dredges and suction dredges are all put to use in the removal of rubble from a reef area.
Numerous adhesive materials can be used in the stabilization practice including epoxy, limestone boulders, and concrete mats. Dislodged corals have a chance for survival if attached soon after a disturbance. Attachment methods include using epoxy, cement, expansion anchors, threaded rods, wires, nails, bamboo skewers, and plastic wire ties Precht All of these processes further aid in reducing the possibility of secondary damage from a disturbance.
One of the most important features for the flourishing of reef health is its structural integrity. Most often this type of damage is caused by vessel groundings and occurrences of blast fishing. It is of the utmost importance that careful consideration be taken when choosing a substrate material to be used in restoration.
Structural integrity repair is restoration of the usually unseen cornerstones of the reef. Another result of frequent vessel groundings, blast fishing, coral mining, and other structurally damaging activities is the loss of topographic complexity. The reestablishment of topographic integrity is vital to the survival of the current collection of plants and animals living in and amongst a reef.
If the correct form of substrate is not chosen for the repair of a reef structure a whole new reef may come into existence depending on what fish and coral are recruited to the new form of grounding. Limestone and concrete are the most common and appropriate materials for the restoration of topographic complexity Precht The method most usually involves placing large boulders or concrete mats over demolished rubble sights or atop sunk or grounded vessels to add suitable stability.
Transplantation has become one of the most popular methods in coral reef restoration. It is seen as the most effective way of providing immediate coral coverage to a damaged reef.
The primary objectives of coral transplantation are to improve reef quality, biodiversity, and topographic complexity. Reasons for the transplantation of corals to a site may include a need to: 1. Immediate increase in coral cover and diversity 2. Increased recruitment of coral larvae as a result of the presence of transplants 3.
Survival of locally rare and threatened coral species when primary habitat is destroyed 4. Reintroduction of corals to areas which are larval supply limited or have very high post-settlement mortality 5. Improved aesthetics of areas frequented by tourists 6. Instant increase in rugosity and shelter for herbivores in bare areas Disadvantages that are just as quickly merited are: 1. Loss of coral colonies from donor reef areas 2.
Higher mortality rates of transplanted corals 3.
While the tendency in those cases may be to fragment corals and expand the nursery, it is important to realize that every coral growing in a nursery is there only temporarily and needs to be outplanted. Good planning and a suitable exit strategy are thus needed to avoid nurseries from becoming too large to manage. Even the best-planned restoration programs can lose funding, momentum, or interest.
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Some of the factors that have contributed to this scenario include: 1 lack of sustained funding beyond the nursery stage; 2 turnover in dive shop and hotel ownership and personnel; 3 vandalism and physical damage to nursery resources; and 4 loss of local support. In these cases, a clear exit strategy is needed to prevent the proliferation of orphan nurseries.
An exit strategy should be an explicit part of the planning process and should clearly identify the scenarios that would trigger the interruption of a project and the steps needed to terminate the restoration project responsibly. At a minimum, an adequate exit strategy would require the outplanting of all nursery corals onto suitable reef habitat and the removal of all nursery materials from the site to prevent these materials from damaging nearby reef resources. This common-sense approach would mitigate negative perceptions of coral gardening in the local community and allow for the re-initiation of future projects in the same area if resources become available or conditions improve.
The first advances in coral propagation within nurseries and the outplanting of nursery-grown corals were achieved by trial-and-error. With the maturation and expansion of this field, a number of programs have developed strong, science-based methods now published in the peer-reviewed literature and as manuals available online Edwards, ; Johnson et al. The next step, outplanting nursery-grown corals onto wild reefs, is still experiencing mixed results, with variable performance of outplants Lirman et al.
Once outplanted, corals cement to the benthos and become natural components of the reef where they experience the same threats and challenges as wild corals. However, nursery-grown corals face novel challenges on present-day reef environments that differ from the ecosystems where they thrived decades ago. Corals are now commonly placed on reefs that have a significantly higher macroalgal cover and lower herbivore densities than historical levels.
The loss of corals has potentially created a scenario in which coral predators that have not declined to the same extent as corals can target outplants and cause rapid mortality. Galvan, , unpublished data.
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Outplanted corals also face potentially detrimental water chemistry conditions where ocean acidification has created reef environments with low aragonite saturation states Manzello et al. An example of the challenges faced by outplanted corals was provided by the unprecedented, back-to-back bleaching events recorded in the Florida Keys in and During these events, both outplanted and wild colonies showed similar patterns of bleaching and mortality that were highly influenced by coral genotype and location C.
Drury, , unpublished data Fig. Considering the relatively young age of the gardening activities in the Caribbean and Western Atlantic, data are still lacking on the long-term survivorship of outplants. However, in Culebra, Puerto Rico, the site of the oldest gardening program in the Caribbean, staghorn outplants deployed in are still alive today E. Hernandez, , personal communication. Carne, , personal communication. Nava-Martinez, , personal communication.
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In addition, one extremely positive outcome of the gardening activities has been the observation of successful spawning of nursery and outplanted staghorn corals in Florida and the Caribbean e. The fact that nursery-grown corals and corals raised from larvae behave reproductively as wild corals lends support to using coral gardening to aid in the natural recovery of depleted populations.
The use of coral gardening methods for species and reef recovery are not without potential negative impacts that need to be considered. The two main ecological concerns, in our opinion, are disease impacts within nurseries and outplanted populations and genetic impacts on the extant populations. By propagating a limited but increasing number of genets within densely populated nurseries, there is the potential that a rapidly progressing disease can decimate nursery stocks.
An additional concern is the introduction or spread of a pathogen from nursery to wild reefs during outplanting. Unfortunately, limited data are available to evaluate the impacts of these concerns. However, reports from nursery practitioners indicate that the prevalence and impacts of diseases on staghorn coral are similar between nursery and wild populations, and between restored and wild populations Miller et al. To limit the spread of disease within nurseries, practitioners commonly remove corals at the first sign of disease and nurseries often have a quarantine area removed from the main nursery where affected corals can be temporarily placed during outbreaks.
While methods like excision of affected tissue and banding the diseased margin using epoxy have been tried to limit the spread and impacts of diseases, these interventions have not been especially successful Miller et al.
Nevertheless, no examples of complete nursery mortality have been reported and diseases commonly run their course leaving plenty of ramets unaffected to continue propagation. In Florida, only corals that are visually free of disease and appear in good health normal coloration can be outplanted onto wild reefs as per permit requirements, providing some level of protection. The increasing use of ex situ coral nurseries e. While such cases have not been reported, practitioners in the US that want to outplant lab-reared corals are required to have their corals certified by a qualified veterinarian prior to transplantation.
Targeted research is clearly needed to fully document the impacts of coral diseases within the gardening framework. Another concern for gardening programs is the role that coral outplants can play on the genetic and genotypic diversity of wild populations, especially considering that the coral species being restored have experienced recent drastic bottlenecks in coral abundance.
In the last few years, genetic sampling has been routinely incorporated into nursery operations and the outcome of these studies can be used to support restoration activities and address these concerns. In Florida, recent findings of high genetic diversity within nursery stocks and wild reefs suggest that these concerns should be tempered and that local populations would benefit from the addition of new individuals Drury et al. The incorporation of genetic sampling into nursery programs can be used to identify and target areas in need of active restoration.