Since 1980, populations of Staghorn (Acropora cervicornis) and Elkhorn (Acropora palmata) corals have collapsed throughout the Caribbean from disease outbreaks with losses compounded locally by hurricanes, increased predation, bleaching, elevated temperatures, algae overgrowth, and other factors.
Once found in continuous stands that extended along the front side of most coral reefs, today these areas have been largely transformed into rubble fields with few, isolated living colonies facing local extinction.
In 2006 NOAA (National Oceanic and Atmospheric Administration) and NMFS (National Marine Fisheries Service) listed elkhorn and staghorn coral as “threatened” species under the Endangered Species Act (ESA) and in December 2012, NMFS proposed reclassifying the two branching corals as endangered. Both staghorn and elkhorn corals are listed as Critically endangered by the IUCN (International Union for the Conservation of Nature and Natural Resources)
At Reef Renewal Cayman Islands, our current method of propagation begins with Coral Tree Nurseries. These nurseries are rows of PVC and fiberglass “trees” that are tethered to the bottom with sand anchors and buoyed with floats that sit just below the surface. This design allows the trees to move freely within the water column and dissipates wave energy, preventing damage both to the tree structure and the corals. Generally, each tree holds a unique genetic strain, or genotype, of coral, and a “full” tree can hold anywhere from 100 to 160 corals.
One of the primary benefits of coral nurseries is the care that can be provided to growing corals. Husbandry activities and maintenance of nursery sites are critical to maximizing coral health and minimizing the incidence of disease, predation, and breakage.
The Coral Tree nursery has proved to be an efficient and effective way to grow and propagate second, third, and future generations of corals through fragmentation. Fragmentation is a process that occurs naturally when corals reproduce asexually. When a large fish or wave breaks a branch off the coral, the branch will continue to grow into a new coral if the water conditions are favorable. We mimic this process in our nurseries by using pliers to cut smaller pieces from existing, large corals. Those fragments get hung back on the same tree, creating more corals of the same genotype. In this way, the Coral Tree nurseries become a self-sustaining approach to grow corals.
After six to eight months of growing in the nursery, our corals are healthy and mature enough to be outplanted to a restoration site. Coral outplanting means moving nursery reared corals to a restoration site. Restoration sites are reef sites that are degraded and damaged and would benefit from our healthy corals growing there.
We take corals from the nursery and outplant them in restoration sites using various methods. Our current methods include attaching corals to bamboo structures, adhering corals to solid substrate using a marine epoxy, and placing corals strategically in areas where conditions seem favorable. Whichever method we use, we tag our corals to keep track of the genetic information and to allow for short and long-term monitoring.
There are many criteria for selecting a restoration site. A few we take into consideration are existing and historical wild populations, depth, water quality, bottom type, size of the area, predator abundance, wave exposure, and the effects of human activities. These site characteristics also play an important role in helping to determine which outplanting method we use and how many corals get placed at that site.
Maintenance and Monitoring
Both coral nurseries and restoration sites are monitored regularly. We check our nurseries for disease, predation, damage to nursery structures, and more, which helps us control and prevent issues before they occur. Our nurseries also receive regular cleaning in order to prevent the overgrowth of algae and fire coral. At restoration sites, we monitor survival rates, tissue paling, disease, and predation, among other aspects. Our process of monitoring and maintenance gives corals another chance at success as we ensure that the coral fragments are in the position to mature and prepare for outplanting and our outplanted corals will continue to grow on their new substrate. Without reattachment, the broken fragments would most likely be unable to attach to the reef substrate on their own and would not survive.