Saturday, November 01, 2008

Semakau Field Trip on 1 Nov 2008

Today, we were off to Semakau again conducting a training for our volunteers. There was a storm earlier in the morning, and I was a little worried that the forest trail will be flooded again, and the animals may be hiding from the increase in freshwater from the rain. Fortunately, everything was fine (except for a few fallen trees) when we cut through the secondary forest and reach the intertidal area.

Most of my photos were not great today, but decided to post most of them so at least my volunteers can check up the ID of what we saw. Again, I chose pufferfish to be my group name for this trip, and I had 10 HSBC volunteers with me practising their guiding technique.

Here a shot of the HSBC volunteers who were with me.

As per usual, there were lots of sand-sifting sea stars (Archaster typicus) on the sandy shore. This is a special one with only 4 arms instead of 5. These sea star can burrow and feed on tiny organic particles (aka detritus) in the sand.

A little upside-down jellyfish (Cassiopea sp.) was found near the sea grass meadow. This jellyfish has symbiotic algae, mostly in its tentacles.The jellyfish thus often remain in an upside-down postion to allow the algae to photosynthesis being exposed to sunlight. Some of the food made by the algae will be shared with the jellyfish.

While we were crossing the seagrass lagoon, we saw 2 long synaptid sea cucumbers (Family Synaptidae). They were busy feeding by swinging their tentacles around them, picking up any tiny organic particles from the substrate and seagrass.

The ocellated sea cucumber (Stichopus ocellatus) was busy feeding on the detritus on the sand when we saw it. However, along with the detritus came lots of sand too, and studies shown that most sea cucumbers were able to selectively feed on mud or sand that is richer in organic matter.

What goes in, must comes out. We were rather fortunate to witness the sea cucumber excreting the sand it has processed, and all the while, still feeding!

The sandfish sea cucumber (Holothuria scabra) is another sea cucumber commonly found on Semakau, and unfortunately, it's commonly found in restaurants on the dining table too. However, note that it must be processed to remove toxins in it before it can be consumed.

Not too far from the sandfish sea cucumber, we also found a dragonfish sea cucumber (Stichopus horrens). Studies shown that sea cucumbers of this genus (which include the ocellated sea cucumber above) do not eject the sticky threads for defense, but they may eject their internal organs when disturbed. When removed from water for too long, they can actually become very limp, looking like they are melting. And in fact, they may eventually disintegrate all together, unless they were return to water soon enough to reverse this process and recover.

This pretty sea slug is a swallowtail headshield slug (Chelidonura pallida). The headshield refers to the broadening at the head which is used to plow beneath the sand surface and help prevents the sand from entering the mantle cavity. The term "swallowtail" refers to the characteristic long split in the tail. This slug feeds on tiny acoel flatworms.

A rather murky shot of a discodoris nudibranch (Discodoris boholensis) here. The term "nudibranch" means "naked gills", refering to the flower-like gills are the back of most nudibranch species.

The gymnodoris nudibranch is a fierce hunter of other slugs, including other gymnodoris nudibranchs! Since nudibranchs are simultaneous hermaphrodites (i.e. they ahve both male and female reproductive systems), seeing another of their own species usually means both sex and food! They will usually fertilise each other in a 69 position, and at the same time try to swallow each other. The slug which suceed in eating up the other will perform the mother's role to lay the eggs, while the eaten slug bascially performed the father's role - not that it has a choice since it's eaten up - and provide nutrients for its sexual partner and future generations.

I have seen this nudibranch many times. It is probably an Atagema intecta, which feeds on sponges.

Near the reef edge, we managed to find the fluted fiant clam (Tridacna squamosa) again. Like the upside-down jellyfish, this clam also harbours symbiotic algae called zooxanthellae in its tissue. The clam gets a considerable amount of food from the zooxanthellae which can make food from the sun.

We usually call this a Persian carpet flatworm (Pseudobiceros bedfordi) due to the pretty patterns on its back. Flatworms are very, very flat, and are in fact made of only 3 fundamental cell layers. And yet, even though they are so thin, they have a brain! The brain is very simple, but that has attracted scientists to study about them, so as to understand our complex brains better.

There were quite a number of these green worm-like things in different lengths swimming around in a few of the tidal pools. This is one organism which I am quite clueless about what exactly it is. A close-up shot shows that it seems to have segments on it's body. So could it possibly be a segmented worm (Phylum Annelida)?

After night has fallen, more animals appear, including many swimming crabs (Family Portunidae). Swimming crabs are very agressive, and generally hunt for little animals like fishes. The last 2 legs of swimming crabs are paddle shaped, which allows them to swim very quickly and also to burrow into the sand.

A lonely kite butterflyfish (Parachaetodon ocellatus) was trapped in a tidal pool. I've seen these butterflyfishes feeding on the tentacles of carpet anemones by darting quickly to the anemone, snap at a tentacle, and quickly make a jerky turn to get away from the other stinging tentacles.

On one of the pile of coral rubble, we saw several onch slugs (Family onchididae). These sugs have simple lungs instead of gills, so they breath air instead of water! When the tide is high, they usually hide in little crevices with trapped pockets of air. When the tide goes down, they will emerge to feed on algae. Some onch slugs can lay a mucus trail while it feeds, so that it can find its way back home after the feeding expedition!

Apart from the above, we also saw a squid, lots of hard and soft corals, sponges, cowries, a noble volute and octopuses etc.

It was certainly an exciting evening for all the volunteers :)

1 comment:

Robert V. Sobczak said...

That is some very unique marine life. It just goes to show, normal is a function of familiarity, and not an absolute.