Transplanted corals attach themselves in pioneering reef restoration project in Seychelles

 Over 25000 nursery-grown coral colonies were transplanted on 5000m2  of degrgaded reef at Cousin photo by Phanor Montoya-Maya

Coral reefs are dying around the world. By the 2030s, 90% of reefs are expected to be at risk from both human activities and climate change. By 2050, all coral reefs will be in danger. Although recent research in Seychelles shows that some of our reefs have bounced back from the massive coral bleaching caused by climate change all is certainly not well.

Nature Seychelles’ pioneering Reef Rescuers project began in 2010. The reef restoration project aims to address the degradation of coral reefs due to climate change, specifically coral bleaching. The reef rescuers project has been using ‘coral gardening’ in underwater nurseries followed by mass transplantation to degraded sites on Cousin Island Special Reserve, Praslin and Mahe. 

“We are very motivated to see these transplanted coral colonies self-attached, growing to become large, natural looking coral colonies,” says Dr. Phanor H. Montoya-Maya, Technical & Scientific Officer in Nature Seychelles’ Reef Rescuers Project. “It is encouraging because the transplanted colonies with their size and shape are adding to the structural complexity of the site, an important feature of a reef that indicates the changes of recovery.”

 Rope nursery with coral fragments for later transplantation photo by Phanor Montoya-Maya

In the discipline of active reef restoration through transplantation of coral fragments, there are many aspects that can help demonstrate the success of a restoration project. For instance, high survival of corals and natural or close-to-natural growth rates may indicate that the conditions in the transplanted site are good for the long-term survival of the nursery-grown coral fragments; fragments can live to be fully developed coral colonies. There is another way to measure the success of a transplantation effort which is counting the number of fragments that have attached themselves without any human help.

Most corals are animals that live attached to the substrate. Attachment is an important stage of the coral life cycle. Either as coral larvae or as a naturally-broken coral fragment, a coral only can grow to become a reproductively mature colony if it is attached or re-attached. Only when attached, can the colony ‘invest’ its energy into important life functions such as feeding, reproduction and defense. A great deal of effort therefore goes into a transplantation project to ensure the attachment of coral fragments.

There are several ways to transplant or attach corals onto a degraded reef. Coral fragments can be placed onto artificial structures or placed directly onto the reef substrate.

 Two species of nursery-grown corals (a and c Pocillopora eydouxi; b and d Acropora cytherea) that successfully self-attached (c and d) and have grown healthy

“We have found that the former is more cost-effective, results in a higher survival rate of coral fragments and improves the positive effect of transplants on natural recruitment” Phanor explains. “In the Reef Rescuers project, we used two types of coral transplantation techniques: we nailed ropes with nursery-grown coral colonies onto the substrate and we also cemented individual coral colonies after cutting them out from the ropes.”

Regardless of which technique is used for assisting fragment attachment, it is very important to know how soon and well coral fragments are self-attaching. Self-attachment refers to the growth of coral tissue onto the substrate. The sooner a transplanted coral colony can self-attach, the sooner it can invest its energy in acquiring its normal shape and growing to become reproductively active.

Monitoring of self-attachment rates at the Reef Rescuers Project has revealed that the nailing technique is not as effective as cementing. Three months after transplantation, self-attachment of fragments in nailed-ropes was found to range 2% to 44% of transplanted fragments per rope. In contrast, cemented fragments showed up to 100% self-attachment.

 Marine cement can be used to speed up the attachment of transplanted coral fragments photo by Phanor Montoya-Maya

“Because nailing resulted in lower self-attachment rates than cementing, we decided to focus all our efforts on cementing the nursery-raised fragments at the transplantation site,” says Phanor. “We pretty much neglected the corals in the nailed-ropes! However, the continued monitoring of the Reef Rescuers’ transplantation site has revealed that the few fragments in nailed-ropes that did self-attach have grown to become healthy adult coral colonies.

We also expect that the transplanted colony may soon be involved in reproduction. If the transplanted corals are contributing to the structural complexity and the breeding coral population of a previously degraded reef, we believe our reef restoration efforts have been successful. Only time will tell and we keep monitoring these and other variables to confirm what seems to be another world-class conservation success for Nature Seychelles.”