Model of coral larvae dispersal shows Sisters' Islands to be source of reef diversity
Chang Ai-Lien Straits Times 25 Sep 15; and AsiaOne
The Sisters' Islands, home to Singapore's first marine park, are also Singapore's "mother reef" of sorts, researchers have found.
The waters around the two islands are the likely source of the country's impressive coral diversity, thanks to currents which can pull coral larvae in to take root there.
When corals there spawn, they then migrate to St John's, Kusu, Semakau and other islands, says the National Parks Board (NParks), which, together with research and consulting group DHI Water and Environment, developed a model to simulate coral larvae dispersal patterns for the first time in Asia.
"This was essentially agent-based modelling to understand the biological connectivity of our reef habitats," said Dr Karenne Tun, deputy director of the coastal and marine branch of NParks' National Biodiversity Centre.
"We looked at our reef habitats and which were 'source' or 'sink' reefs. From there, we can look at which areas are most important for conservation and make better management decisions."
When corals spawn, the eggs and sperm released into the water join to form free-floating larvae, which float in the water column until they find a suitable home, usually a hard surface they can latch on to.
NParks' new technique to simulate coral larvae dispersal patterns takes into account a complex interplay of factors to track the patterns of the tiny, lightweight larvae during their travels, including hydrodynamics, predators and their response to temperature and exposure to air.
What the researchers found: The country's reefs are generally well connected, with larvae able to flow freely among them. The southern Sisters' Islands, surrounded by waters with sufficiently strong current, are ideally located .
"If we can improve the reef quality, there's a good chance that corals there can spread their progeny throughout Singapore," said Dr Tun.
The currents around Singapore, however, are too strong for most larvae to enter or leave local waters.
"So for our coral reefs to survive, the system has to be self-sustaining," she explained. "We cannot depend on larvae coming in from outside our waters."
So it is apt that the Sisters' Islands Marine Park has been designated Singapore's first marine park.
The 40ha park, about the size of 50 football fields, comprises Sisters' Islands and surrounding reefs, as well as the western reefs of nearby St John's Island and Pulau Tekukor. Its ecosystem supports corals, anemones, seahorses, fish and other marine life.
NParks, which manages the marine park, will open dive trails there to allow the public to experience the rich sea life it holds, and is also using the area for research.
Despite massive redevelopment, Singapore's marine biodiversity remains rich. More than 250 species of hard coral have been recorded in our waters, about 40 per cent of the types of corals found in South-east Asia, and around one-third of the global total.
And since Sisters' Islands have proved to be an ideal nursery, other coral colonies are already being transplanted there from areas undergoing development.
A project to relocate coral colonies to protect them from the impact of the Tuas Terminal development has yielded positive results, for instance.
The corals were moved from the Sultan Shoal, south-west of Singapore, to three southern sites at St John's and Sisters' Islands, and about 80 per cent, or 2,300 out of 2,800 coral colonies, were moved successfully.
And amid works to expand the Semakau Landfill, more than 700 coral colonies were moved from a lagoon there to the marine park.
The ambitious goal is to develop a "gene tank" nursery at Sisters' Islands to nurture the rarest of specimens found in local waters, to increase the odds of such corals flourishing again.
"We will do a very targeted search and harvest of rare or not widely distributed corals, and transplant some of them to the nursery," said Dr Tun.
Dr Lena Chan, the director of NParks' National Biodiversity Centre, said it will also be applying modelling to mangroves and seagrasses.
"Besides corals, seagrasses and mangroves are intricately related, and our marine organisms spend part of their life in one or the other," she said.
"Hence such modelling will enable us to conserve and manage our marine biodiversity better, in a science-based manner."
