Coral nurseries are the key to Acropora survival in the USVI and worldwide

Throughout the Caribbean, two corals belonging to the Acropora family staghorn (A. cervicornis) and elkhorn (A. palmata) are species many people might not know much about, or the major role they play in the functionality and beauty in a coral reef ecosystem. The Staghorn coral gets its name from its complex yet rounded branches that look similar to deer antlers. Elkhorn has larger thicker branches that are flat similar to elk or moose antlers.
Occurring in shallow water around local bays and offshore islands in the US Virgin Islands, these two corals are easy to identify with light brown to orange color and sprawling branches. Within, these branches are teaming with life as they provide essential habitat and protection for countless fish and other marine species.

Elkhorn coral reef
Staghorn coral reef

These Corals are Under Threat

Despite the important ecological and economic benefits these corals provide, these and other species in the Caribbean are under threat. Compounding stressors include extreme temperature, pollution and disease. The cumulative effects of these stressors have resulted in a population decline of 80-98% in both Staghorn and Elkhorn corals since the 1980s.

Both species are now listed as “threatened” under the Endangered Species Act and listed as “critically endangered” in the International Union for Conservation of Nature (IUCN) Red List in 2008.

The continued loss of these coral ecosystems and the services they provide will weigh heavily on many Caribbean islands’ economies and the Virgin Islands is no exception. An economic report from Burke and Maidens 2004, estimated the total value of the ecosystem services coral reefs provide in the Caribbean between US$740 million to US$2.2 billion a year. Therefore, it just makes “cents” to do something to help these corals species come back from the brink of extinction. In light of this devastating decline, Acropora species now require active restoration to maintain and increase the populations until they can persist on their own.

Coral Nurseries Provide a Solution

UVI Marine Science graduate student Colin Howe monitors coral “trees”. These coral fragments will be transplanted to form new reef systems.

A relevantly new method of large scale coral restoration programs developed in the Red Sea in 1990’s known as “coral gardening” has increased in popularity within the Caribbean. Chelsey Young, a natural resource management specialist at NOAA and colleagues conducted a review of restoration efforts and research around the Caribbean. They showed that by 2012, 14 different Caribbean islands now contain over 60 coral nurseries. Coral nurseries, targeting mostly the Staghorn corals, contain underwater structures to attach corals to grow. Nursery methods take advantage of the natural process of asexual reproduction and the rapid growth rates of the Acropora to produce multiple colonies from a small sample taken from the wild.

St. Thomas is Home To Two Coral Nurseries

Coral fragments are outplanted in optimal locations. In about four years these fast growing corals will be old enough to reproduce on their own.

Here in St. Thomas, The Nature Conservancy (TNC) has two coral nurseries. These nurseries are comprised of floating coral trees where the coral are hung and allowed to grow in optimal conditions. These conditions reduce macroalgae competition and predation from coral-eating organisms, and also increase light and water flow which the corals love. Additionally, being suspended in coral trees allows these corals to grow in every direction which lets them grow more complex branches. Once the corals get large enough, branches are clipped and transported in large buckets of fresh seawater to a new location.

Stopher Slade a coral reef restoration scientist at TNC has been working for with TNC for 5 years. Over the past few years he has taken on many students from the University of the Virgin Islands as interns, to teach the best way to care for and out-plant corals in St. Croix and St. Thomas. With a bit of practice, a single diver can plant up to 50 fragments on the reef in a single day. After about 4 years these fast growing corals will be old enough to reproduce on their own and help increase the coral population on their own. Another consideration for out-plant sites are locations were the currents will carry any offspring to other nearby shallow water habitats thus making these corals do the rest of the work.

Collaboration at Work

Coral fragments are ready to outplant.

The Nature Conservancy and the University of the Virgin Islands have collaborated to learn more about coral nurseries and to repopulate the local coral reefs. The main goal of TNC and other coral gardening programs are to replace as much of the corals that have been lost in the Caribbean as they can. Hopefully with more hard work and Caribbean-wide collaboration, enough corals will survive and persist on their own. Through internships and collaborative field work with UVI and TNC, 200 corals were planted in July 2016 alone. 6,148 more were planted prior to that by TNC. Current research on the distribution, resilience and growth of acropora corals in new locations can increase not only our understanding of these species, but also increase the likelihood that most of the fragments planted will reach sexual maturity. Together with innovative research, community awareness, and active community involvement, our hope is to return the Virgin Islands shallow reefs, back to breath taking, vibrant and diverse coral reefs, healthy and abundant fish population, but most importantly and a functioning marine ecosystem for future generations to enjoy.

This guest post was submitted by UVI Marine Science graduate student Colin Howe. Colin, featured in this article, is in his second year of graduate research and has devoted his thesis to the Acropora Coral.

Stopher Slade a coral reef restoration scientist at The Nature Conservancy and student Colin Howe are enroute to outplant site.

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