Monday, October 01, 2007

Semakau Landfill Walk with NUS High

Telescopium telescopium, Archaster typicus, Stichopus horrens, Gymnodoris rubropapulosa

On a normal guided walk at Semakau Landfill, you will never get to hear the guides saying the above scientific names.

But today, it's different!

We have 7 groups of Biology students from NUS High, and we were told to use the scientific names and terms! Most of the students just returned from a field trip to Tioman, and were already introduced to most scientific terms. I heard that they even had to do a transect there!

My group, the Sea Slugs, comprised 10 students, and Jenn Chye was my assistant. The students were not too happy about the group name though, and I had a hard time trying to convince them that slugs were really wonderful animals :)

Here's Luan Keng, our coordinator from the Raffles Museum of Biodiversity Research who took the last boat. Realised that I hardly feature her in my blog, so decided to snap a photo of her :P

Again, one of the first animals we saw was a mudskipper (Family Gobiidae). It was just like yesterday!

As the tide was still a little high, we spent a bit more time scanning the sandy area before the seagrass lagoon. We saw quite a number of snails, including the whelk (Nassarius sp.) on the left and a telescope creeper shell (Telescopium telescopium). The whelk even has a little sea anemone attached to its shell! When we saw it, it was waving its narrow siphons, probably sniffing for dead animals to feed on. The creeper shell, on the other hand, feeds on organic material and algae on the sand surface.

Just when we were examining the telescope creeper shell, one of the students noticed a shrimp lying on the sand. It's a snapping shrimp (Family Alpheidae)! These shrimps have an enlarged claw which has a special tooth on one finger which fits nicely into a depression on the other finger. The shrimp will hit the depression with the tooth really hard that it resonates, and this is actually strong enough to stun its prey or ward off predators.

Yesterday, we saw a land hermit crab, but today, we saw a striped hermit crab (Clibanarius infraspinatus) instead.

There were lots of sponges (Phylum Porifera) at the sandy area just before we enter the seagrass lagoon. Sponges are simple animals which has lots of tiny holes and a few bigger holes on them. To feed, they suck water through their tiny holes and they will pick out the edible particles. The filtered water will then be pushed out of the big holes. Do you know that bathroom sponges used to be made from sea sponges? Nowadays most sponges were made from petroleum though.

Just near the sponges, there were lots of sand-sifting sea star (Archaster typicus).

Yesterday, I got the Dunman High students to hold up their hands for the group shot, and so today, I decided to get the NUS high students to do the lift-up-a-leg pose instead.

We also saw several types of sea cucumber, including 2 species of the genus Stichopus - the ocellated sea cucumber (Stichopus ocellatus) on the left and the dragonfish (Stichopus horrens). Read from some online resources that sea cucumbers of this genus do not eject the sticky threads for defense, but they may eject their internal organs. When remove from the water for too long, they can actually "melt", become very limp and eventually disintegrate all together. However, if they are not too badly "melted", they are able to reverse this process and recover.

This is yet another sea cucumber call the sandfish (Holothuria scabra), and it is edible! However, it is actually toxic and must be properly treated before it can be eaten.

Again, we saw a noble volute (Cymbiola nobilis) with its eggs. Wonder how long does it take to lay all its eggs.

In the coral rubble area, we also saw a heart cockle (Corculum cardissa) and a scallop (Chlamys sp.)

Someone also found a little upside-down jellyfish (Cassiopea sp.). This jellyfish has symbiotic algae which photosynthesises and provide food for the jellyfish. The algae are mostly in the jellyfish's tentacles, and thus they photosynthesises better when the jellyfish is upside-down.

The highlight of the trip is usually the knobbly sea star (Protoreaster nodosus), which were among the biggest sea stars in local waters. These days, we have been seeing knobbly sea stars with wounds and scars. Some of the knobs look like they were biten off. We have no idea what has happened actually. Could there be some parasite in them, or are there any predators attacking them? Read some where that some pufferfish feed on knobbly sea stars.

An finally, a SLUG! Our group name!

To be precise, this slug is actually an orange-spotted nudibranch (Gymnodoris rubropapulosa). Nudibranch means "naked gills". Can you see the flower-like gills on its back?

Nudibranchs are hermaphrodites, meaning that they have both male and female reproductive organs. So when they meet they often fertilise each other. The situation is a little different with this nudibranch, however, because gymnodoris feeds on other slugs! So when they meet another slug of the same species, it could mean sex and food at the same time. As they fertilise each other, they will try to swallow each other too! Eventually, one of them may be eaten up, and the remaining slug will perform the role of the mother and lay eggs.

All too soon, it was turning dark. It's just so unfortunate that the low tides were so late these few days and we couldn't have more time to explore the intertidal area.

Still, it had been an enjoyable trip and the NUS High students also a very enthusiastic bunch.

Do check out these other blog entries by the other guides on today's trip!

- My first virgin guide! by Siyang
- First time guiding at Semakau by Juan
- Semakau Inter-Tidal Walk on 30 Sep 2007 by July

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