Populations of elkhorn coral, Acropora palmata, have declined over 90% in their Caribbean range since the 1980s. Due to their importance as ecosystem engineers and their ability to structurally stabilize reef environments, establishing a regional mapping and monitoring program was crucial to determine the relative importance of various spatial, temporal, and physical factors affecting the survival of wild A. palmata. Starting in 2010, wild A. palmata colonies were monitored along the Florida Reef Tract (FRT) from Southeast Florida to the Dry Tortugas. Results suggest colony fate was influenced by the amount of initial living skeletal area, geographic location, season, year, and the presence of other stressors such as disease, storms, and corallivorous snails. The synergistic interaction between these factors led to extirpation at three sites. The results offer insight into regional variability in survivorship and aid in identifying where remnant populations of A. palmata may persist along the FRT. This in turn can help guide future restoration efforts of this threatened coral.

Population declines of Acropora cervicornis, largely a result of bleaching and disease, led to its 2006 listing as Threatened under the US Endangered Species Act. Unfortunately, natural recovery of populations through fragment regeneration and sexual recruitment remains inadequate to offset population losses of over 90 percent. As a result, the Coral Restoration Foundation developed techniques to outplant A. cervicornis colonies to reefs throughout the Florida Keys. The growth, survival, and condition of 2,428 A. cervicornis colonies from 20 transplant projects started between 2007 and 2013 in the upper Keys were evaluated through photogrammetric analysis and in situ monitoring. The average size of A. cervicornis transplants after six years was approximately 50 cm in diameter. Mortality was initially low, but generally increased after approximately two years. Average mortality across all projects approached 90 percent, but there was large variation among projects. Growth rates measured as maximum diameter of colonies averaged 10cm/year during the first two years, then plateaued in subsequent years. Corals outplanted to spur-and-groove habitats generally grew larger than outplants in low-relief hard-bottom habitats. Genotype effects related to growth, survival, and condition were not statistically significant. Size frequency distributions documented that small colonies dominated after four years. Results from the outplant projects were used to estimate the amount of time and effort needed to restore three reefs (Carysfort, Molasses and Conch), using success criteria identified in NOAA’s Acropora Recovery Plan (ARP). Under current conditions, the decadal timeframes to meet ARP success required repetitive (annual) outplanting effort, scaling up capacity to outplant more colonies by at least an order of magnitude, and improved outplanting methods. Alternatively, if stressors are significantly reduced, then repopulation could occur quickly based on existing capacity to outplant corals and typical rates of population growth. In the meantime, current outplant capacity and results contribute significantly to the persistence of the species in locations where they were historically abundant but are currently absent.

Staghorn coral, Acropora cervicornis, is a threatened species that has declined more than 90% throughout the Caribbean since the late 1970s due to mortality from disease, hurricanes, bleaching, and predation. Outplanting of nursery-reared corals has become an established technique to enhance A. cervicornis populations. A growing body of literature documents encouraging results of restoration efforts, but most of these studies have only fate-tracked outplanted colonies for one or two years. During 2017, we revisited A. cervicornis restoration sites established during 2012 as part of an effort supported by the American Recovery and Reinvestment Act (ARRA). These sites offered a unique opportunity to evaluate the longer-term fate of A. cervicornis restoration efforts and evaluate potential factors that influence the success of these sites. However, fate tracking A. cervicornis colonies long-term is challenging as individual colonies readily fragment. Consequently, we did not attempt to fate track individual colonies as has been commonly done in short-term surveys, opting to estimate total A. cervicornis biomass by surveying the entire restoration site. We paired these surveys with surveys of benthic flora and fauna and characterized the physical structure of the sites to evaluate how these factors potentially affected site-related differences in A. cervicornis biomass. Hurricane Irma prevented the completion of this study as originally conceived. However, the A. cervicornis surveys we completed revealed substantial variation in coral biomass among the sites. Biomass had increased considerably at two Dry Tortugas sites and at one middle Keys site compared to two lower Keys sites and other middle Keys sites. A post-Irma survey of A. cervicornis biomass at those sites we had previously surveyed found considerable differences in survival. The middle and lower keys sites closest to the storm were heavily impacted, but the two sites in the Dry Tortugas had comparatively minor loss of A. cervicornis biomass.

The Reef Restoration Program initiated by Oceanus, A.C supported by MARFund, SUMMIT Foundation and other partners is focused on strengthening resilience and adaptation potential of coral reefs to promote recovery of associated species of fish and invertebrates. The Program involves the transplant of 10,000 colonies every year and identification of genetic material from healthy donor populations to increase diversity in restoration sites, thereby promoting natural resilience and resistance to climate change and local stressors. Oceanus has initiated and maintained reef restoration actions in no take areas of the Mexican Portion of the Mesoamerican Reef for four years now. To date, the Restoration Program activities are developed in at least 20 sites of 6 different locations in Mexico (Puerto Morelos, Cozumel, Mayakobá at Playa del Carmen, Sian Ka’an, Xcalak and Mahahual) and it has initiated work in Roatán Island in Honduras. After 5 years sites are starting to show visible changes of recovery. Results from monitoring have shown that on average >80% of the transplanted colonies from previous years have survived in the restoration sites. Due to the continuous input of new colonies (small sizes), average of maximum diameter in sites with multiple generations was 30.2 cm(+- 14.5 D.E.), and more than 30% of the trasplants, averaging all sites, are larger than 20cm. Cover of living tissue in each colony ranged from 12.2 cm2 to 3964.8 cm2 with an average of 363.9 cm2. Oldest transplants in Puerto Morelos, Xcalak and Mayakobá are now growing exponentially. In Puerto Morelos, old transplanted colonies are now being part of the landscape in one of the first restoration sites with more than 90% of the colonies being larger than >160cm2. After achieving that size, every additional year of growth, the proportion of the colony that spawns will increase according to maturity. Sexual reproduction of transplanted colonies is the ultimate goal, as it will start the multiplier effect of restoration, sending hundreds or thousands of genetically diverse larvae and recruits to new sites on the reef.

For 10 years we have been conducting experimental coral restoration effort in the Bahamas through direct transplantation and outplanting of from nurseries using Acropora spp. and other species. An important part of these efforts from their start has been the development of a hierarchical monitoring program to assess the success of our coral restoration efforts and to determine what factors can influence success. Within the restoration study system off Abaco, Bahamas, source colonies have been genotyped and fragments from each source colony individually tagged and grown at different depths in line nurseries at two locations. New growth from fragments in the is cut to outplant to reefs annually or biannually. Outplants are then individually tagged and their survival and growth tracked annually. Physical parameters of the site such as temperature are also monitored. In addition to tracking the individual outplants the monitoring program includes assessments of naturally occurring coral populations, benthic cover and fish communities on experimental reefs and controls. Results of monitoring efforts show how growth and survival of colonies varies based on outplant site, source colony, conditions in nurseries and size of the outplanted fragments. Between reef survival varied considerably and could be attributed to differences in coralivorous snails (Coralliophila abbreviata) at sites. The effect of coral outplants on fish and benthic communities at restoration sites on Abaco and other parts of The Bahamas are also discussed. Based on these results, we have developed recommendations for conducting coral restoration in The Bahamas, which may be applicable to other locations. Finally, we touch on experimental outplanting of other species and factors that have influenced their growth and survival.

Acropora cervicornis was restored on two sites (Jeff Davis and Playa Lechi) on Bonaire and monitored for 1 year. Playa Lechi is located in front of the main city of Kralendijk while Jeff Davis is 7 km north. On each site 50 one meter quadrats were installed covering approximately an area of 150m2. On each quadrat 25 colonies from one of 11 genotypes grown in the CRFB nurseries were attached and growth in terms of coral cover was monitored during one year. Results show large differences in growth between the two locations. On average coral cover at Jeff Davis increased linearly (0.06% per day or 21.6% per year) and similar in every quadrat from 16% at the start to 38% after one year with very little mortality. Genotype had a very small effect on the net growth rate. In front of the main urbanised area growth was erratic, mostly negative, and often non-linear. On average coral cover had decreased here from 17 to 7.7% after one year; 40 of the 50 quadrats had decreased in coral cover, 7 had increased and 3 ended at the same size they were installed. Environmental conditions in front of Kralendijk are presumed to be responsible for the lack of growth and high mortality of the restored staghorn corals here. Under normal conditions (Jeff Davis) however coral cover increases rapidly and, based on current nursery dimensions, CRFB will be able to restore approximately 1200m2 of staghorn reef each year.

The widespread bleaching event in 1998 caused significant disturbance to coral reefs within the Western Indian Ocean, resulting in up to 95% coral mortality within the Seychelles. In 2011, a large-scale coral reef restoration project was implemented to facilitate reef recovery and enhance ecosystem services within the Cousin Island Special Reserve. Between December 2012 and June 2014, a total of 24,431 nursery-grown coral colonies from 9 different species were transplanted in 5,225 m2 (0.52 ha) of degraded reef at the no-take marine reserve. Coral nubbins, collected from survivors of the 1998 event and corals of opportunity, were raised in in-situ midwater rope and net nurseries. To measure the effects of restoration on natural recovery, ecological monitoring was completed before and after initial transplantation, at the transplanted site and at the adjacent control sites (degraded and healthy). In 2012, before intervention, live coral cover, juvenile coral density (< 5 cm in diameter) and fish density at the transplanted and degraded sites were similar. In 2014, live coral cover, juvenile coral density and fish density at the transplanted site were 5.5, 1.6 and 1.4 times higher than at the degraded control site, respectively. Following a series of natural disturbances throughout 2015 and 2016 (including a severe bleaching event) live coral cover decreased dramatically across all sites. Surviving corals (i.e. thermally resilient) were identified, stocked and transplanted (1,837 colonies between 2017 and 2018) in an ongoing effort to repopulate the reef. Preliminary results from ongoing monitoring show significant signs of reef recovery and the positive effects of transplantation are still apparent, whereby juvenile coral density and fish density at the transplantation site remain higher than at the degraded control site. This work highlights that the positive effects of large-scale reef restoration continue even after the occurrence of natural disturbances, which may be related to prevailing structural complexity following coral mortality. The next phase of the project aims to utilise ex-situ nurseries to microfragment massive and encrusting species and cultivate heat resilient corals based on genetic markers.