25 January 2009

Are there seagrasses at Kranji Nature Trail?

Twas low(ish) tide, wet and windy, but I really wanted to find out if there were seagrasses at Kranji.
It's been a long time since I visited this stretch of mangroves, which lies next to the main Sungei Buloh Wetland Reserve.

With the new Sungei Buloh Wetland Reserve masterplan, the Trail is now part of the Reserve which has long looked after the mangroves there. I noticed quite a lot of replanting going on. How nice to see the baby mangroves everywhere.On one side of the Trail are lots of lush soft mud with meandering streams and intriguing mangrove trees.On the other side, the Johor Straits with Johor Baru just across. There is also a large kelong just off the area.

The Trail is a great way to have a closer look at some typical mangrove critters.
The white Beccari's Tent Spider (Cyrtophora beccarii) builds a gorgeous tent web which is like a delicate circus tent held up by lots and lots of silk. I am still astounded by how a tiny creature could build something so complex.The white spider usually hides in the white silken tunnel in the middle of the web. But this one was out and she seems to be fixing up her tunnel. Extending it?Nearby, a hardworking team of Weaver ants (Oecophylla smaragdina) was busy trying to stuff something into their leafy hideout which is built out of a living leaf, 'sewn' together by the silk produced by the ants' larvae.

In the mangroves, you might find the oddest things on leaves.This shiny animal is a clam! It lives on mangrove trees! It is the Mangrove jingle clam (Enigmonia aenigmatica). Like other bivalves, it has a two-part shell. One valve is flat and stuck to a hard surface (leaves, tree trunk, roots). This valve has a notch or hole in it. The animal secretes byssus threads through the hole to stick to the hard surface. A young animal is more mobile and can move around by using its extendible foot. Snails are plentiful on mangrove tree leaves, trunks, roots and all over the mudflats. These elegant periwinkles are probably Littoraria melanostoma which means black-mouth. And I always forget to take a photo of the shell opening which is supposed to give rise to their name.I remembered to have a peek today and indeed, there is a black portion at the shell opening. I carefully placed the periwinkle in a safe place on the branch so that it can emerge and cling onto the tree when the tide comes in. If we don't do this, the poor snail may wash away and die. I also took the opportunity have a closer look at the periwinkles in my fact sheets and realised some were Littoraria conica and Littoraria carinifera! I must now take a closer look at these snails. So much to see when we're out exploring!The most adorable snail must be these bug-eyed little red snails. They are probably Red berry snails (Sphaerassiminea miniata) and countless numbers were creeping about on the mud.Even the slugs of the mangroves are somewhat different from those I see elsewhere. This is an Onch slug (Family Onchididae). It is quite ornately festooned with complicated bumps.Here's a closer look at the upperside. The underside is lemon yellow! The only time I've seen this Onch was in mangrovey areas on our North shores. I have no idea what it is.And among the mangrove trees, small patches of tiny seagrasses! This is Beccari's seagrass (Halophila beccarii). It is often overlooked as it just looks like scum.Especially at low tide when the leaf blade are all stuck to the mud or sand. But this tiny plant has a rosette of five tiny oval leaves which are often striped. This seagrass is listed as 'Critically Endangered' on the Red List of threatened plants of Singapore. So far, I've only seen this seagrass at Chek Jawa, Pulau Ubin and at Sungei Buloh Wetland Reserve. Truly a precious seagrass.

Unfortunately, I didn't get to look further out on the mudflats, but on the higher shores, I didn't see any Spoon seagrass (Halophila ovalis) or any other kind of seagrasses. I probably need to have a special trip just to look for seagrasses and not get distracted by all the other amazing stuff in the mangroves. Sigh.

Such as... what is this strange-looking Bruguiera with not-so-red flowers?Having been bit by the mangrove bug, I take a really close look and realise it's probably just a pale Tumu (Bruguiera gymnorrhiza).Although the sepals are tantalizingly spreading a bit away from the propagule, and the flowers are really pale, it's probably Bruguiera gymnorrhiza because it the flowers are solitary, large and have 12 calyx lobes (the pointy things on the thick flower calyx).Also, the bark of the tree is smooth without lenticels. So it isn't a rary Bruguiera like Brugueira hainseii (which has bumps called lenticels all over the bark) and has smaller flowers with 9-11 calyx lobes.

For more about how to tell apart these tantalizing Bruguieras, check out the fabulous paper "The Bruguiera (Rhizophoraceae) Species in the Mangroves of Singapore, Especially on the New Record and the Rediscovery" of which Dr Jean Yong is one of the authors. The PDF can be downloaded from the Raffles Museum of Biodiversity Research website. It has lots of details and wonderful photos as well. Go have a look.

There were a lot of Avicennia out on the flats, but I didn't see any with characteristics of Avicennia marina. There were also lots of Rhizophora mostly R. apiculata, and some Xylocarpus granatum. It got dark pretty soon, so I had to stop looking at the trees.

It's fun looking more closely at our common mangroves to figure out if they are something else. More mangrovey adventures tomorrow!

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