Abundant life in artificial reefs

From left: Prof Chou (holding a coral from the Pocilloporidae family), Lionel and Dr Toh

NUS researchers have found that artificial reefs deployed in Singapore waters have over time become home to thriving marine life, contributing to the development of underwater communities and ecosystem functioning in areas where the original coral habitat had been degraded. The research was led by Lionel Ng Chin Soon, a PhD student with NUS Biological Sciences. The team members comprised Adjunct Research Professor Chou Loke Ming and Dr Toh Tai Chong from the Tropical Marine Science Institute (TMSI) at NUS. The research paper was published inAquatic Conservation: Marine and Freshwater Ecosystems in April.

Over a decade ago, numerous artificial reef modules known as Reef Enhancement Units (REUs) were positioned at seven plots off Singapore’s southern islands, including Kusu, Lazarus and Sisters. The 50-cm high REUs weighed about 10kg each and were made of fibreglass with sand incorporated onto the external surface to resemble natural rock more closely. They were anchored to sandy and rubble areas on the reef, serving as raised and stable settlement surfaces for coral larvae.

The researchers surveyed the plots in 2014, visiting the sites up to twice a month throughout the year, and found that REUs at six of the seven plots remained intact. They discovered that the marine communities at the REUs were more diverse than in 2004, when the plots were last surveyed. Reef fauna — crustaceans, fishes and molluscs — were actively using the REUs for food and shelter. Hard corals constituted 11 per cent of the lifeforms present at the artificial reefs in 2014, an increase of more than 55 times from 2004, when its presence was scarce. 

Sessile organisms, which included soft corals, sponges, anemones, bivalves and crustaceans, as well as mobile organisms, became more abundant too, with close to 120 types of these organisms observed in 2014. “Artificial reefs can enhance biodiversity and the surface area also enhances coral attachment and growth,” said Prof Chou.

One of the REUs deployed in a reef off Singapore’s southern islands 

REUs had clearly assimilated into the reef environment that they had been situated in, evident through the interaction of mobile creatures such as crustaceans and cephalopods with the structures. “Some corals had even grown from the surface of an REU at Kusu to the surrounding reef,” said Dr Toh. 

The researchers also observed that the marine communities inhabiting the artificial reefs varied across the plots surveyed, suggesting possible influences by differing conditions at the sites, such as water quality or intensity of the currents. Interestingly, there was a shift in the types of coral between 2004 and 2014. Corals belonging to the families Pocilloporidae, Merulinidae, Acroporidae and Poritidae were most abundant in 2004; in 2014, however, Dendrophylliidae, along with Merulinidae, dominated. Some sites, like the ones at Raffles and Kusu, also exhibited higher coral cover and diversity than at Lazarus.

“Artificial reefs can enhance biodiversity and the surface area also enhances coral attachment and growth.” – Prof Chou Loke Ming

While artificial reefs is a common reef restoration strategy, its contribution over a longer time frame has not been well understood. The team is thus heartened by the insights gathered from this study. Noting the value of monitoring, Lionel said, “In reef restoration, follow-up and long-term monitoring are very important for you to be able to tell whether your efforts are working or not.”

In the next phase of the study, the researchers hope to dive deep into how specific factors of artificial reefs, such as surface complexity as well as crevice orientation and size, can enhance biodiversity. 

This article was first published in NUS News http://news.nus.edu.sg/highlights/abundant-life-artificial-reefs