23 August 2009

Mangroves of Chek Jawa: where is the silt?

A cool misty morning, I spent a glorious glowing sunrise monitoring seagrasses with TeamSeagrass.
Then headed out to check the mangroves that ring the high shores of Chek Jawa.

Here's Richard and Yen-Ling still hard at work on their transect. Behind them, the boardwalk and viewing tower at the mangroves of Chek Jawa.
Chek Jawa is one of the few shores left in Singapore where the mangroves and seagrass ecosystems are found next to one another as it is naturally meant to be. There is a delicate flow of nutrients between the ecosystems, and various marine life depend on these ecosystems.

Unfortunately, today I noticed that there has been severe erosion of the shores at Chek Jawa's mangroves.
You can see the exposed roots of the trees on the high shore.
Also disconcerting to note was the lack of soft, silty mud. This area near the sluice gate used to be treacherous to negotiate. I would get stuck up to my knees here in the past. But today, I walked easily on very hard sand and hardly got my booties muddy.
Still, the special mangrove trees that I remember from the past were still there.

There is a majestic Nyireh batu (Xylocarpus moluccensis) in this mangrove. This tall tree has magnificent short buttress roots and peg-like pneumatophores (breathing roots). And today, it was flowering! This is my first time seeing flowers of X. moluccensis.
The flowers look very much like those of the more common Mangrove cannon-ball tree (Xylocarpus granatum). But the two kinds of trees can be easily distinguished by looking at their bark and leaves.

X. granatum has bark that peels in patches giving a pattern that resembles camouflage uniforms, and leaves with more rounded tips.
X. moluccensis has bark that is fissured along the length of the trunk, and leaves that are more pointy and eye-shaped.
Another kind of Xylocarpus that is very rare in Singapore is Nyireh (Xylocarpus rumphii) which is generally found on rocky shores and not muddy mangroves. Besides its location, this tree has leaves that are almost heart-shaped with obvious veins. Here's photos of the X. rumphii seen on St. John's Island.
Chek Jawa has lots of very tall Bakau minyak (Rhizophora apiculata). These trees have stilt roots that loop out from the trunk, as well as prop roots that emerge from the branches and hang down like a curtain around the tree.
Deeper among the other mangrove trees were several tall Tengar (Ceriops tagal) trees. These have spoon shaped leaves and propagules with white collars.I looked for the Lenggadai (Bruguiera parviflora) that is supposed to be here. And I found a very tall tree that might be it, but it wasn't flowering or bearing propagules so I couldn't be sure.

Draped among the trees are the tough climbing Hoyas (Hoya sp.). With thick succulent leaves and pretty waxy flowers in small clusters. This particular one looks like Hoya verticillata.
Another common mangrove tree at Chek Jawa is Api-api bulu (Avicennia rumphiana). There were a few of these trees that are being affected by erosion. But this allows us to have a closer look at the exposed root structure. The vertical pencil-like pneumatophores emerge from horizontal underground roots.
Another special tree right next to the boardwalk is the Dungun (Heritiera littoralis). With silvery leaves and buttress roots. This one also had its roots exposed probably due to the erosion. This tree is listed as 'Endangered' in our Red List.
At the high water mark were several Mempari (Pongamia pinnata) trees. I'm not sure if they grew there naturally or were planted. As they were near an area of planted trees. These trees are listed as 'Endangered' in our Red List. Unfortunately, their roots are also being exposed due to erosion.
NParks is also replanting special mangroves at Chek Jawa. I only had a chance to quickly check out the Tumu berau (Bruguiera sexangula) that were planted next to the boardwalk. Wow, the little trees are still blooming and forming propagules! This tree is listed as 'Critically Endangered' so it's good to see the trees doing well.
As I hurried out to meet up with the rest of TeamSeagrass, I passed the Gelam (Melaleuca cajuputi) trees planted along the trail. The leaves resemble those of Acacia and give off the typical medicinal smell when crushed. The leaves are indeed used to distill 'tea-tree oil' or 'kayu putih' which has a wide range of traditional medicinal uses.
And this tree along the trail was in full bloom! The flowers sure look like those of Penaga laut (Calophyllum inophyllum), but the leaves of this tree were very long and narrow. Is it another kind of Calophyllum?
There are many MANY more trees to look at and ponder upon at Chek Jawa. And you can see them from the comfort of the boardwalk. But I didn't have time to look at much more.

The erosion on the high shores and lack of silt is worrying. It would be ideal to establish regular and proper monitoring of various aspects of this precious shore. The work of TeamSeagrass is a start, but much more can and should be done.

While I was doing the mangroves, Kok Sheng was checking out the outer shores of Chek Jawa including the coral rubble area. He is the best person to do this as he had done many health-checks on Chek Jawa for his project following the mass deaths there in 2007. Visit his blog to find out what he saw today.

For more blog posts about this trip see the list of links on the TeamSeagrass post of this trip.

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