Romancing the coral
Published September 16, 2010
From Aquarist Leah Neal
Elkhorn coral was once the most abundant species of coral in the Caribbean and the Florida Keys. In the last 30 years, approximately 90 percent of it has been lost due to disease, environmental factors and human activity. The Elkhorn is so diminished that it was the first coral species to be listed under the Endangered Species Act (2006).
The National Aquarium has been a member of Project SECORE (SExual COral REproduction), an international partnership of public aquariums and coral scientists focused on preserving coral reefs through breeding and reef restoration, for the last five years.
Through this program, my colleagues and I have played an active role in perfecting human-assisted sexual reproduction of Elkhorn coral. We've participated in many collection trips and logged many hours raising the adult coral colonies for display.
As a result, visitors to our Washington, D.C., location can now see one of the few exhibits of Elkhorn coral in an aquarium setting. This new Buck Island exhibit is the direct result of perfecting spawn collection techniques in the wild and growing the coral to maturity in a laboratory. But our work to save endangered corals is not finished just yet.
These techniques are now being groomed for equal success in the wild, as scientists hope to reseed Caribbean and Atlantic beds with a genetically diversified coral able to sustain itself.
So I packed my bags and headed for Curacao, Netherlands Antilles, in late August to participate in our next SECORE mission, a workshop to kick off a three-year project based at the Curacao Sea Aquarium to build a field extension for the express purpose of reestablishing and monitoring new Elkhorn and Staghorn corals.
The first order of business was to sit in on several lectures to gain a background knowledge of the project, its current status and future goals. Then we dove right in and began our quest to grow new coral.
The next several days were spent building out five tanks that were set up in a brand-new exhibit space at the Sea Aquarium. These tanks needed to be ready to hold larvae in two to three days. Along with the plumbing, we built 20 kriesel tanks with manifolds that are meant to keep the larvae moving just slightly as they develop.
At night, we were out collecting the spawn from these two coral species. We broke into two groups that dove two separate dive sites so that we could make sure that the gametes (eggs and sperm) being collected were genetically diverse.
We looked for “staging.” This means that with the naked eye you can see egg bundles that have been pushed to the top of the polyp. When we saw this, we covered the branch or branches very delicately with a collecting net, and then sat back and waited. Usually, within 10 minutes the coral would begin to release the bundles. They would float up in our nets and end up in our collection cups. The spawning usually lasts anywhere between 10 and 20 minutes. As soon as the gametes were collected, it was a race back to the lab for fertilization. The pictures below show the collection process.
Once the fertilization process was complete, the larvae were added to our newly built kriesels, where they remained for the next four to five days. During this time, the larvae were very fragile and needed round-the-clock care. We spent our days and nights monitoring, stirring and changing the water while the larvae were developing.
Once the larvae develop their cilia, they begin looking for a place to settle. Upon seeing this stage of their life cycle, we began to prepare settling tanks. These tanks consisted of layering the entire bottom of a plastic container with the outplanting tripods, ceramic structures upon which the newly formed primary polyps will be introduced back to the ocean. The pictures below help show the magnitude of the kreisels and settling tanks!
Although the workshop is over, the work continues, as the trip leaders and Ph.D. students stay behind to begin the restoration effort. The group will put the corals back out onto the reefs at regular intervals, so that they may find the life stage that is the most stable for reintroduction.
Photos courtesy of Paul Selvaggio