Coral restoration on seawalls

Researchers from the Tropical Marine Science Institute (TMSI) at NUS and NUS Biological Sciences, with a team of dedicated volunteers, have successfully transplanted six hard coral species onto artificial seawalls on Lazarus Island, off the southern coast of Singapore. The transplanted corals showed sustained growth, and high survival rates of close to 90 per cent on average, demonstrating that coral transplantation onto subtidal seawalls is not only feasible, but also helps to create a sustainable marine environment in urbanised coastal areas. The research was published in Ecological Engineering last November.

Man-made structures such as seawalls and breakwaters, which replace natural shorelines and their biodiversity, are increasingly erected to alleviate the impact of rising sea levels and frequent flooding predicted to accompany climate change. More than 60 per cent of urban Singapore’s 200km shoreline consists of seawalls.

To increase the ecological value of seawalls, scientists and conservationists have been working on transplanting various organisms onto seawalls. Scleractinian corals, in particular, are prime candidates for transplantation as they form the main framework of coral reefs, which support 25 per cent of the world’s marine species. They also provide protection of the shoreline by reducing the impact of waves and erosion rates.

Most efforts in transplanting and ecological engineering have been focused on the intertidal zone of seawalls. Speaking of the NUS study, TMSI Research Fellow Dr Toh Tai Chong said that it is one of the first to demonstrate that coral transplantation, when done properly, can be carried out in the subtidal regions of the seawall too. “In situations where there has to be urban development, we can try to mitigate the damage by relocating some of the corals to create new communities in man-made areas,” he added.

In 2014, 216 fragments generated from six coral species were collected from Sultan Shoal, a small island about 5.5km from mainland Singapore. These fragments were secured on coral nursery tables for nine months at Lazarus Island. Live corals from the nursery were then transplanted to granite seawalls nearby.


Coral fragments are secured at nursery tables for some nine months

Twenty-five volunteers from non-governmental organisations, private companies and various government agencies assisted with the work over a one-year period. TMSI researchers taught and trained the volunteers about coral restoration, including proper techniques, to ensure that the process remained scientifically rigorous.

The transplanted corals performed well after the shift, with mean survivorship after six months at 89.7 per cent. Two species exhibited complete survival, while three species registered survival rates between 91 and 97 per cent.

Dr Toh also shared that coral transplantation is usually a laborious and costly process, but assistance from volunteers can help ease the cost. The study showed a 5 per cent reduction in labour costs with the help of volunteers. “We estimate the costs can be reduced further, up to 22 per cent, if the extent of community involvement was even greater. With proper guidance, community involvement can also be a useful tool in habitat conservation programme to encourage a greater sense of public ownership in natural heritage,” explained Dr Toh.

This study was conducted as part of the “Enhancing Singapore’s Coral Reef Ecosystem in a Green Port” project funded by the Maritime and Port Authority of Singapore.