Starting in the Summer of 2019, the Eco Divers program has been authorized to expand their stock of corals to include Elkhorn (Acropora Palmatta). Authorization was also approved to increase the variety of Staghorn (Acropora Cervicornis) genotypes in our nursery program.
Our first inclination was that the Elkhorn had to be a priority. Discussions with outside groups indicated that their experience with Elkhorn had been fraught with difficulties. Many issues were limited to the normal problems faced by any coral nursery corals. Predators, bleaching or disease outbreak. However, considering the depth of our nursery structures, my greatest worry was of bleaching as the corals settled into their new, deeper homes.
Our nursery sites are anchored in roughly sixty foot of water and the structures are raised above the sandy bottom to a depth of forty to forty five foot. Our Elkhorn were collected in less than five foot of water and we were certainly worried that the sudden change in depth could cause the various Zoozanthellae algae living in the corals to experience sudden masive changes resulting in a temporary bleaching from stress. I had experienced results similar to this in my own home aquariums years ago, and made sure to examine the corals regularly to record any indication of stress or bleaching activity.
I also admit that the physical strength of the Elkhorn required us to handle the corals more than I would have liked. A hacksaw was used to create our first round of fragments and the physical trauma of all this activity could have been a chance for our corals to suffer tissue loss or even the introduction of diseases during the period while they healed.
Instead, we found the corals were able to adapt easily to the deeper water. Harvesting them in early Summer meant that they were in their best health and appear to have adjusted to their new depth without issue. The physical contact with our volunteers and fragmentation efforts also appear to have healed over fully without any loss of our coral fragments.
In fact, our Elkhorn corals have not only adjusted to the new depth, but the damage caused from fragmenting the original colonies has begun to heal. In time, we can carefully remove these corals from the nursery structure and fragment them even more to allow us to create hundreds of smaller fragments that will be able to grow in a uniform manner across all three of our nursery sites.
Our Staghorn corals have established themselves over the previous three years under our care. Loss due to disease is currently at zero and even predation has claimed only a handful of individual corals. Bleaching and storm damage is avoided by our decision to keep our nursery structures in deeper water. Adding four new genotypes to the nursery program proved to be a straightforward process. Identifying healthy sections of coral to harvest wass tretched over a period of two years allowing us to identify strong specimens that should prove hardy over the upcoming years.
So now we have expanded our program to allow for considerable growth. As we face the 2020 season, we are careful to allow our new corals a chance to adapt before they are further fragmented. And observation of our outplant project corals becomes a critical issue. While our nursery program has been remarkably efficient, our experience with corals on the reef is that damage from predators such as Damselfish can easily lead to disease outbreaks.
It was the appearance of what seems to be type 2 White Band disease that put a stop to our outplanting in 2019. Nursery sites were unaffected, but multiple areas of wild corals showed significant infection rates. So we are left with a serious potential for infection. This potential is a massive threat to our corals long term survival and required some thoughtful planning to provide the safety required for our program.
I should back up one step and explain why we even bothered to outplant corals in the first place. Our goal was never to physically replace selected areas of the reef with nursery grown corals and then declare that we “Saved the Reef”. Instead, our goal was only to create concentrated areas of coral that would be able to spawn every Summer. These concentrated areas of coral spawning allow the reef to create an abundance of genetically diverse corals.
So I have to look back and consider why we have to put our project corals on the reef structure. Any section of reef is going to house possible predators or diseases. This leads to the potential degradation of our coral spawning over the upcoming years due to loss or disease. However, our nursery structures do not seem to have the same likelihood of risk. In fact, our nursery structures have encountered only one common issue over the last couple of years. They grow too large and have to be trimmed down to allow us to outplant reasonably sized colonies.
My proposal is that direct return of our corals to the local reef might not be the best long term use of our corals. Instead, we should create a series of small, evenly distributed coral nurseries. two to three structures at most for each site. five genotypes could be reasonably hung on each structure totaling ten colonies of each genotype. This is the exact same volume of coral originally intended for our outplant program. The only difference is the safety of remaining in a permanent nursery structure.
Coral spawning is the key to long term coral management. In 2018, we filmed our coral nurseries spawning. In 2019, we intend to increase that exposure and data. Areas around our nursery sites show a dramatic change in coral cover after each spawning event and have exceeded our best, optimistic plan for coral distribution. So I believe that it is reasonable to to push for this same concept to be expanded and used to safely seed our local reefs with healthy coral larvae.