Since the 1970s, the world’s corals have been declining at an alarming rate. Rising temperatures, acidification from carbon emissions, disease, and pollution have all played their part. While statistics may offer a bleak outlook, scientists are showing us it’s not necessarily all doom and gloom. For the first time, a group has managed to successfully rear a critically endangered species of coral to sexual maturity. These developments suggest that it may be possible to use this novel nurturing method to rehabilitate coral populations that have suffered losses.
“It’s great news that the method is working,” study author and SECORE coral reef ecologist Valérie Chamberland told IFLScience. “But we now have to start researching how to apply this in concert with other coral reef management techniques. If the conditions aren’t good enough on the reef, our technique won’t work. We need to make this a more holistic approach with other methods.”
Described in Bulletin of Marine Science, the research has focused on Caribbean reefs that, over the past four decades, have witnessed an 80 percent decline in coral, prompting the instigation of various management and restoration projects. The species targeted is elkhorn coral (Acropora palmata), an ecologically important reef member that helps defend against damage from storms and provides a haven for an abundance of marine life. Unfortunately, it was almost wiped out by an outbreak of disease in the mid-70s and subsequently earned critically endangered status under the IUCN Red List of Endangered Species.
The researchers therefore wanted to develop a viable technique to aid the recovery of this species. While other projects throughout the Caribbean have generally focused on a method called “coral gardening,” which involves pruning small fragments of coral, growing them in nurseries and then returning them, this isn’t an ideal solution because it reduces the genetic diversity of the reef. Populations with limited gene pools struggle to adapt to change, such as rising temperatures or disease, making it more difficult for them to survive in the long term.
To overcome this, in collaboration with the University of Amsterdam and the Carmabi Research Station, SECORE scientists began by collecting sex cells (gametes) released by numerous different elkhorn coral colonies located near the island of Curaçao. These were then returned to the lab and fertilized in a test tube. Successful embryos were then allowed to settle on clay tiles and reared in a land-based nursery for a year, before being planted back on the reef and monitored.
Nets used to capture coral gametes. Credit: SECORE
Encouragingly, seven out of nine colonies survived and continued to grow on the reed, reaching the size of a soccer ball in just four years. Importantly, two of these colonies were observed releasing gametes, showing that in this short period the corals are able to reach sexual maturity. This is important, because it not only suggests that the technique could be used for reef population, but the possibility of sexual reproduction represents a way to maintain coral genetic diversity.
The work is certainly not over yet. Chamberland points out that the next stage involves working out a way to do this on a larger scale. “Mass production of coral babies hasn’t been done yet, so we need to find a method to rear and outplant large numbers in a non-time-consuming way,” she added. The team is also working on applying this method with other species, and has already had encouraging results for the slower-growing brain coral.