'Christmas' wish for Pulau Ubin takes root

Plan to turn former aquaculture ponds into mangrove habitats
Audrey Tan Straits Times 23 Dec 16;

Christmas is just around the corner and boughs of imported holly are already decking many halls and building facades.

But Singapore has its own version of the Christmas holly - and it can be found growing in the wild, in places such as Pulau Ubin and the Sungei Buloh Wetland Reserve.

The country has three species of the sea holly - or jeruju, as it is known in Malay - all of which grow in mangrove habitats.

They have spiny leaves similar to the temperate plant used in Christmas decorations, although the local versions are not closely related to the Christmas holly.

The latter can be found in western Europe, the British Isles and parts of the Mediterranean.

"The 'holly' appellation of the sea holly is purely based on the leaf shape," said botanist Shawn Lum, a senior lecturer at the Nanyang Technological University's (NTU's) Asian School of the Environment.

"The most consistently 'holly-like' of the three local species is Acanthus ilicifolius. In Latin, ilicifolius means leaves like a holly," added Dr Lum, who is also president of the Nature Society (Singapore).

The other two species of sea holly are Acanthus volubilis and Acanthus ebracteatus.

Singapore's sea hollies do not always have lobed leaves with spiny edges. They sometimes have leaves which are spineless.

"Spininess appears to be a feature of younger leaves and may be affected by water stress, seasonality and light intensity," said Ms Ria Tan, 55, a naturalist who runs the wildsingapore.com nature blog.

She is among a group of people - including National University of Singapore (NUS) scientists, fish farmers, fishermen and naturalists - who are hoping that the sea holly, as well as other mangrove plants, will naturally regenerate in the abandoned aquaculture ponds on Pulau Ubin, an island north-east of the mainland.

The 150ha of mangroves on the island make up about 20 per cent of Singapore's mangrove forests.

The Restore Ubin Mangroves (RUM) initiative aims to make use of an ecological approach to rehabilitate the habitats.

This is done by first recreating conditions suitable for mangrove growth in the abandoned ponds.

"We collect data on the rehabilitation sites, such as their elevation and tidal flooding, and compare this with a nearby natural mangrove forest," said NUS Assistant Professor Daniel Friess, who is leading the scientific study.

"For example, if the data shows that the rehabilitation site is too low, then we can use these maps to guide where to bring in dredge material to raise the elevation so that mangroves will grow more successfully."

Scientists are now working on the first phase of the RUM initiative, which involves mapping out existing mangrove and abandoned aquaculture sites using equipment similar to a digital theodolite - which uses laser beams to map out elevation changes.

The next phase of the project will involve changing the elevation of the abandoned aquaculture sites by adding soil or digging channels to mimic areas of natural mangrove growth, said Mr Wong Tuan Wah, group director for conservation at the National Parks Board (NParks).

The latter is working with the RUM team on mangrove rehabilitation.

This will be the first time that this method is being used to transform aquaculture ponds to mangroves in Singapore.

Prof Friess said it has been successfully applied in many projects in Florida in the United States, Thailand and Indonesia.

Said Mr Wong: "Mangrove forests are vital to the coastal zone in Pulau Ubin as they protect the shoreline from erosion.

"Restoring mangrove ecosystems would also conserve the habitats for native biodiversity like fiddler crabs and mudskippers."

The RUM team is also conducting activities to raise awareness about Singapore's rich and diverse mangrove habitats, through free guided walks along Pulau Ubin's sensory trail, for example.

Said Ms Tan who leads the walks: "Mangroves are amazing. They are plants that can live in the sea, they are full of animals, they are fascinating and part of our coastal ecosystem."

•To sign up for the mangrove walks, visit rum-initiative.blogspot.sg/

VIDEO: Spot some holly at Pulau Ubin's mangroves http://str.sg/4dma

Singapore's sea hollies with healing qualities
Audrey Tan Straits Times 23 Dec 16;

Like the Christmas holly, Singapore's sea holly plants sometimes have spiny leaves.

Research by plant expert Jean Yong has shown that sea holly plants have variable leaf shapes in response to environmental factors, such as exposure to sunlight and salinity.

"In the harshest localities of any mangroves, where plants receive full sunlight and are often fully immersed in seawater, two species of sea hollies - the Acanthus ilicifolius and Acanthus ebracteatus - will develop very spiny leaves," said Dr Yong, an eco-physiologist at the Australian Research Centre for Mine Site Restoration.

He added that, in general, sea holly plants which receive greater shade, and/or freshwater, have rounder, less spiny leaves.

"We hope to find out which the predominant factor is - whether it is sunlight exposure or salinity - in determining the ultimate leaf shape and spine development."

Another unique trait about sea holly plants is their ability to deal with salt. While some mangrove plants keep salt from entering in the first place, sea hollies take salt in and discharge it through salt glands on their leaves, said botanist Shawn Lum, from Nanyang Technological University's (NTU's) Asian School of the Environment.

Here is more information about Singapore's sea holly plants.


This is a common mangrove plant that grows up to 3m in height. Its leaves are used to treat rheumatism and wounds and can be used to make a softening cream. In addition, a concoction of the leaves can be taken with the stems to promote longevity, or with the roots to improve hair conditions, and treat sores and snake bites, according to the National Parks Board (NParks).


This species is considered vulnerable. It can grow up to 2m in height. Its seeds are sometimes boiled to be used as ingredients in cough mixtures.


This species can grow up to 8m in height. This is considered the rarest among the three Acanthus species, said Dr Yong, and can be found only on Pulau Ubin and Pulau Tekong and in Sungei Buloh and the Western Catchment areas. This species also produces the least spines on its leaves.

Audrey Tan

•Source: NParks, Dr Jean Yong, Dr Shawn Lum



Mangrove plants from the genus Rhizophora have iconic prop roots that extend over a large area. These help the plant to hold on to the soft and unstable mud and improve stability of the tree. Wood from such trees is used to make charcoal.


This plant is critically endangered; the International Union for Conservation of Nature estimates there are 200 mature individuals left in Singapore, Malaysia and Papua New Guinea. In Singapore, there are 13 trees, says the National Parks Board. They can grow up to 33m tall, and are found in the back mangroves or elevated areas less frequently inundated by seawater.


This common plant can grow up to 20m in height. It has roots that help it absorb oxygen in the mud. It can also selectively absorb water by excluding salt from the seawater it takes in. Its bark can be used as medicine for diarrhoea and occasionally malaria. An extract of the bark is also used as a source of tannin and dye.


This colourful bird, native to Singapore, is rare. It has been sighted at the mangroves in Pasir Ris Park, Pulau Ubin, Pulau Tekong and Sungei Buloh. It builds dome-shaped nests on or close to the ground. This species is suspected to be in moderately rapid decline as a result of habitat loss and degradation.


This venomous snake calls the mangroves of Singapore its home but is endangered here. It feeds on lizards, frogs and other small animals, possibly small birds.

Audrey Tan

•Sources: NParks, IUCN, Dr Jean Yong, David Tan, wildsingapore.com

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