Saturday, February 23, 2008

A Walk with the Trainees at Semakau

While the other Semakau guides were on guiding duty today, I was there for another reason - to run a practical session for the new guides!

And here're some of the things we saw today.

When LK was telling the trainees more about the great billed heron (Ardea sumatrana), I suddenly spotted one in one of the landfill cells and shouted to the rest. Unfortunately, my camera zoom wasn't fantastic, and so I only managed to get a blurry shot. This is supposed to be the tallest bird in Singapore, and usually they can only be found on our offshore islands or the western coast, usually a pair on each of location. However, on a few occasions I've seen 4 of them on Semakau - a pair on each far end of the intertidal flats!

The sand-sifting sea star (Archaster typicus) used to be very common even on our mainland shores, but these days, they are mostly found on the offshore islands too, as many of our natural sandy shores had been reclaimed.

Found this juvenile mangrove horseshoe crab (Carcinoscorpius rotundicauda) creeping just underneath the sand. This armoured critter is not a true crab though, and is more closely related to spiders and scorpions. Often called living fossils, these animals were already around even before the dinosaurs roamed the Earth!

The hunter-seekers found this dead stingray, which I had some problem identifying because the edges were already badly chewed off by other animals and the colour was already quite off. My guess is that it could be a blue-spotted stingray (Dasyatis kuhlii), as I could vaguely see lots of off-coloured spots on its back, but can't really say for sure. Will really appreciate it if anyone can help to ID it. (Update: ST says in his blog that it is probably a coachwhip ray, Himantura uarnak. This ray is also called the black-spotted whipray. Certainly looks more like it rather than the blue-spotted stingray after comparing the photos.)

Not to be confused with the blue-spotted fantail ray (Taeniura lymma) which is more rounded in shape, the blue-spotted stingray can grow to a disc width of at least 40cm sometimes (about the size of the one we saw today). The last time I saw a living one was on Beting Bronok, but that was much smaller with its disc width around 15cm.

After crossing the seagrass meadow, I found this dragonfish sea cucumber (Stichopus horrens). 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.

For at least the past half a year, I've been finding noble volutes (Cymbiola nobilis) laying eggs on both our northern and southern islands.

We also managed to find the resident gigantic carpet anemone (Stichodactyla gigantea). Couldn't find the resident ocellaris clownfish though...

And yet another great find by our hunter-seekers - a heart cockle (Corculum cardissa)! Such a brilliantly coloured one some more!

What's more fascinating was - the other side was in a totally different colour! Bright blue! Unlike most other clams which have their valves flatten like plates, this clam has its opening of the valves cutting across the centre of the 'heart'! Can you see the line running down the middle?

Our hunter-seekers managed to find us 2 ocellated sea cucumber (Stichopus ocellatus) today. Closely related to the dragonfish sea cucumber, it can suffer from the "melting effect" too.

Our very-hardworking hunter-seekers also found us several types of nudibranchs! They found 4 orange-spotted gymnodoris nudibranchs (Gymnodoris rubropapulosa) together on some seaweed. Nudibranch means "naked gills", as many of them have their gills exposed. You will be able to see the flowery gills on the back of the above nudibranchs.

Two other species of nudibranchs found were the polka dot nudibranch (Jorunna funebris) and the green ceratosoma nudibranch (Ceratosoma sinuata).

We sure have lots of luck with sea cucumbers today, as we also saw 2 stonefish sea cucumbers (Actinopyga lecanora) which are usually found among rocks and corals in the coral reef...

And a sandfish sea cucumber (Holothuria scabra), which can burrow into the sand. This sea cucumber is a very popular commercial species, especially during the Chinese New Year period. It is edible, but must be properly processed to remove the toxins.

And here's me with a knobbly sea star (Protoreaster nodosus). To think that I've seen them so many times, but had never taken a photo with them! Finally did it today. The knobbly sea star is one of the biggest sea stars in Singapore waters, and can grow up to 30cm wide.

All in all, it is yet another enjoyable trip! Hopefully it had been a good experience for the trainees too :P

See also:
1. Semakau Inter-tidal Walk on 23 February 2008 by ST
2. Semakau Inter-Tidal Walk on 23 Feb 2008 by JL
3. Training at Semakau intertidal by KS

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