Semakau Walk on 3 June 2007

The sun was just "popping out" of Pulau Jong when we arrived at Semakau Landfill Last Sunday. Today, I had a group of HSBC volunteers with me. They were training to be nature guides, and also with me was Siyang on his first OJT trip.



We were a little early today, and thus NEA did not provide any transport to drive us to the entrance to the intertidal area. We had to walk all the way, but it was a sunny and beautiful day, so everyone's spirit remained high! :)



After bashing through the secondary forest, we reached the sandy shore of the intertidal zone. Near the seagrass lagoon were lots of sponges (Phylum Porifera) which come in all colours.



In the picture above, you can see some greenish blue sponges and some brown sponges, competing for space, with some sea lettuce (Ulva reticulata) dangling around. Sponges are simple animals which have many tiny holes on them to suck in sea water. Any tiny organic particles in the water, will be captured and eaten. The water will then be pushed out of bigger holes along with any wastes.

Just near the sponges, we also saw a few common seastar (Archaster typicus).



A sea star uses sea water instead of blood to support its body and to move around, so don’t take them out of water too long, as it is very stressful for them. Seastars are also able to regenerate broken arms, provided that the central disc is not damaged.

Near the seastar zone, our hunter-seekers also managed to find this sea cucumber.



I was quite excited to see it, as this was only the second time that I had seen it on Semakau. Called the ocellated sea cucumber (Stichopus ocellatus), it has false "eyes" on its body.

And nearby in the coral rubble area, we saw its relative, the warty sea cucumber (probably Stichopus horrens).



Also called the peanutfish, dragonfish or golden sea cucumber in the sea cucumber trade, this sea cucumber has also been observed to be able to reproduce asexually by fission, and they can detach a piece of skin when attacked. Sea cucumbers of the genus Stichopus supposedly have an unusual defense mechanism where they can become completely limp and eventually disintegrating all together if taken out of the water for too long. However, if they are not too far gone, they have the ability to reverse this process and recover.

We also saw two other species of sea cucumber - the stonefish (Actinopyga lecanora, below left), and sandfish (Holothuria scraba, below right).



These sea cucumbers are edible, but must be properly treated before they can be eaten because they contain toxins. Like the sea stars, sea cucumbers are made of a tissue which allow them to keep their body soft when they are moving around, but yet in an instance, they can turn rock hard to protect themselves when they feel threatened. And by the way, do you know that a sea cucumber actually breathes through its anus?

At the coral rubble, we also saw the usual things like the scallop (Family Pectinidae, below left) and the hairy crab (Family Pilumnidae).



Scallops are also filter feeders like the sponges, though they generate the water currents in a different manner. During high tide, they open their shells slightly to suck in water and collect edible particles. At low tide, they will shut their shells tightly. Scallops can also "swim" by flapping their valves.

The hairy crab is a master of camouflage. It has tiny hair on it to collect sand and dirt so that it can blend in to the surrounding. It is poisonous, so don't ever cook and eat it!

Our hunter-seekers also found a carpet anemone (Stichodactyla sp.) and an anemone shrimp (Periclimenes brevicarpalis).



The carpet anemone has short, sticky tentacles which sticks little animals that blunder into it. The tentacles have stinging cells that will paralyse the animals, and the anemone will move the food to its mouth in the centre using the tentacles.

We also saw may hermit crabs (Diogenes sp.) and branched anemones (Phymanthus sp.).



They were many fanworms (Family Sabellidae) in the various tidal pools too.



These worms live in tubes, and have feathery fans stuck on their heads. The fan is used to filter edible particles in the water so that the worm can feed on them.

Nearer the coral reef area, we started seeing more corals, including the sunflower mushroom coral (Heliofungia actiniformis, below left) and the maze coral (Platygyra sp.).



The sunflower mushroom coral is actually a single living animal. It has symbiotic alge (aka zooxanthallae) which lived in it, which provide it with additional nutrients from photosynthesis.

The maze coral is a hard coral which has merged and elongated, wavy walls. It is actually a colony of animals. The coral animal (aka polyps) live in the structure made mainly of calcium carbonate. Doesn't that remind you of us living in HDB flats?

We also saw a few nudibranchs. The name nudibranch actually means "naked gills". In the picture below is a polka dot nudibranch (Jorunna funebris) on the left, and a bohol nudibranch (Discodoris boholensis) on the right.



Nudibranchs are simultaneous hermaphrodites, meaning each of them has both male and female reproductive organs. They often fertilise each other when they mate. Sometimes, one may take on a male role, the other a female role. Most nudibranchs live for about a few months to a year, and they usually die after laying eggs.

And of cause, the star attractions for the day must be these knobbly seastars (Protoreaster nodosus).



We were joking that it looked like a family of seastars, as the one in the bottom right of the above photo was a juvenile less than 10cm wide. The adults were like 25-30cm wide. But of cause, nobody knows whether they were really a family :P

And here's the traditional group shot with the knobbly seastars!



As the tide was rising, we managed to get to the reef edge to find the merten's carpet anemone (Stichodactyla mertensii), which in one of my previous trips I had found false clownfishes on them.



Sadly, the clownfishes were not around today.

Walking back, we spotted this long-spine sea urchins (Diadema setosum). These sea urchins have long, sharp and brittle spines which break easily, do don't handle them! They normally graze on algae and also scavenge.



We also saw two flatworms (Class Turbellaria) . Sorry Siyang, I'm not exactly sure of the exact ID of these flatworms as well :P



Flatworms are so flat that they can easily get into tiny crevices to find preys and also to escape from predators.

As the tide is rising fast, we had no choice but to turn back. We soon reached the sandy area again. There were lots of sand balls made by the sand bubbler crabs, and also several cast made by the acorn worm.



Acorn worms are named after their acorn-shaped head. They are very fragile and so please don't try to dig them out, as they may just break!

We had to bash through the forest again and finally reached the washing-up area. This was followed by a land tour of Semakau Landfill, and a video presentation given by NEA.

For more stories of this trip, you may check out the following entries:
- Semakau Tidal Walk - 3 June 07 at the Manta Blog
- Semakau Inter-Tidal Walk on 3rd June 2007 at the Where Discovery Begins blog
- Morning Semakau! at the Urban Forest blog