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Onto Bigger and Better Things: Boulder Corals Thrive after Reef Outplanting

Boulder corals are among many coral species whose growth and survival have been affected in the face of climate change and disease. Stony coral tissue loss disease is one of the major stressors that boulder corals face. The cause of the disease is unknown, but it has been making its way through the Florida Reef Tract since 2014. It destroys living coral tissue, leaving multiple blotchy lesions in its wake. Once a colony is affected, it will die within weeks or months.

The loss of boulder coral species leads to a range of consequences, as they provide many ecological and economic benefits. Boulder corals, among many other stony coral species, provide coastal protection from storm surges, refuge, nursery and feeding areas for many marine organisms, and support fishing and scuba diving industries. For these reasons, CRF™ has expanded to include growing, propagating, and outplanting a number of different stony boulder coral species to combat this loss.

Left to right: Orbicella faveolata, Orbicella annularis, Montastraea cavernosa, and Siderastrea siderea. ©Shane Gallimore/Coral Restoration Foundation™

These various species include mountainous star coral (Orbicella faveolata), boulder star coral (Orbicella annularis), great star coral (Montastraea cavernosa), and massive starlet coral (Siderastrea siderea). By outplanting a variety of these species and genotypes, the reefs natural biological diversity is upheld, promoting a healthy and resilient reef.

The Coral Trees used for the boulder corals are similar to those used for the Acropora corals, wherein they are suspended vertically in the water column. This increases water flow and limits predation and competition. However, boulder corals prefer to grow upward on a horizontal plane, rather than hang vertically in the water column. To fulfill this need, CRF™ has altered the trees to have flat branches that can hold trays of plugs that the corals are epoxied to.

Moreover, the branches are staggered at 90 degrees, parallel to the ocean floor, in order to maximize the amount of sunlight reaching the coral. The branches are attached to the tree using bolts. This technique makes it easier to install new trays, remove them, and transport them for outplanting. Each tree has a failsafe line of 1200 pound monofilament that will keep the tree’s PVC pipes intact in the event that they come apart.

Restoration Associate, Dan, installs a new boulder coral tree in the Tavernier Nursery.

© Coral Restoration Foundation™

Once the boulder corals grow large enough to be outplanted, areas are cleared using a hammer on the reef for 2-inch holes to be drilled. Each boulder coral plug is then inserted and epoxied into an individual hole. This is done in clusters as big as 10 corals at a time in fairly close proximity to promote fusion. Fusion is when individual coral colonies fuse their exoskeleton together, creating a larger and stronger structure on the reef. This robust colony provides marine habitat to support life on the reefs and protects the coastline from high wave energy.

Staff and interns outplant Orbicella faveolata on old mortality in hopes for new growth.

©Shane Gallimore/Paige Carper/Sabine Bailey/Coral Restoration Foundation™

This program has seen many successes over time. The first boulder coral polyps were collected three to four years ago. These polyps have developed and grown enough to propagate them through fragmentation to increase and sustain our boulder coral population. Furthermore, the boulders see little to no stressors from the fragmentation. Outplanting has also proven to be very successful. Their survival rate after one month of being restored on the reef is over 90%. Furthermore, when predation is a factor when the corals are placed on the reef, they have proven to be capable of recovery.

Three month development and recovery of Orbicella annularis coral outplants.

© Coral Restoration Foundation™

In the future, CRF™ hopes to receive permits to restore a larger number of boulder corals across the Florida Reef Tract, ranging from Northern Carysfort Reef, all the way down to New Found Harbor Reef.

A healthy and wild Orbicella faveolata colony nearby leads a path for our young corals to follow. ©Shane Gallimore/Coral Restoration Foundation™

Additionally, a new method is in the works with NOAA compliance to be able to outplant a much larger number of boulder corals on the reef at one time. This would be done through a method that may include a small, ocean safe structure that has prefabbed holes that would elevate the boulder corals off the reef, further preventing predation, sedimentation, and would speed up the out-planting process. The CRF™ team is excited to continue its mission of restoring the Florida Reef Tract with the help of these amazing boulder corals!


About the Author

Darcy graduated from Indiana University with a B.S. in Biology and a certificate in Underwater Resource Management.  Growing up landlocked in the Midwest, her love for the ocean began with yearly family trips to Florida.  Once in college, she got involved in an underwater science program and obtained her Rescue Diver certification.  Additionally, she was able to study abroad in both Grand Cayman and the Dominican Republic.  These trips inspired her to get involved with ocean conservation so that beautiful reef habitats can be sustained for current and future generations alike.  She aims to one day be a research scientist with a focus in corals and is enthralled to learn everything she can from the incredible team at CRF™.

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