Saturday, June 07, 2008

Semakau Walk on 7 Jun 2008

Today, I was back at Semakau with a group of students from Jurongville Secondary. MY was with me as an on-the-job trainee, and our group name was Hermit Crabs.

During the boat ride, SY spotted dolphins swimming near our boat. But unfortunately, I was on the lower deck then and didn't get to see them. But all the students and teachers who saw them were really thrilled!

As usual, after reaching the island, we had to walk all the way to the intertidal area.

Again, I got a traditional shot of my participants crossing the seagrass meadow. Seagrasses are very important to both humans and the other marine organisms. Many of the seafood we eat, such as fish and shrimps, spend part of their lives living among seagrasses, as there are lots of food and hiding places from predators. And also because of that, many marine animals use seagrass habitats as nursery grounds for their young.

And the usual wacky shot too! :P

And as we were crossing the seagrass meadow, TC who's leading a group behind found an ocellated sea cucumber (Stichopus ocellatus). 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.

And not too far ahead on the sandy shore, we found lots of sand-sifting sea stars (Archaster typicus). A sea star uses sea water instead of blood to support its body and to move its tube feet, so don’t remove them out of water for too long, as it is very stressful for them.

Had not wanted to disturb this moon snail (Polinices mammatus) which was feeding, and thus didn't take it out of the sand. And why do we know it's feeding? Well just before this, we saw it grabbing a little snail with its huge foot. To feed, it will wrap its foot around its prey to try to suffocate it. It can also secrete an acidic liquid to soften the shell of its prey, and use its radula (something like a tongue) to slowly create a hole on on the shell of its prey, so that it can feed on the latter while they are still in their shells.

Our hunter-seekers also found us this little ovum cowrie (Cypraea ovum). Cowries feed on algae, and their shells are so smooth because they wrap their mantle around them which prevent them from getting scratched by rocks and sand.

There were many fanworms (probably Sabellastarte indica) in many of the tidal pools. Fanworms use the feather-like structures to collect any edible particles in the water.

We can often find pufferfishes on our trips too. Not really sure of its ID though. While they are very toxic, pufferfishes are very much valued as a delicacy among the Japanese (and of course, Japanese food lovers too!). Only chef with the proper license can prepare pufferfish dishes, but still once in a while, we see cases of people dying from eating pufferfish!

Semakau is also a great place to see a high diversity of corals, and the above is an anemone coral (Goniopora sp.). Also called a flower pot coral (it certainly looks like a pot of little flowers when the coral polyps are out), this is actually a hard coral which has a hard skeleton made with calcium carbonate. And every little flower you see above is an individual animal!

We can usually find a few pretty nudibranchs at Semakau too. The above is a marginated glossodoris nudibranch (Glossodoris atromarginata). Nudibranch means "naked gills", and the gills are the flower-like structure on the back of the nudibranch. These pretty animals are actually sea slugs, i.e. snails without shells or with internal shells.

Many nudibranchs, such as the glossodoris nudibranch and also the black phyllid nudibranch (Phyllidiella nigra) above. Phyllid nudibranch are rather well-known for the fact that they are very poisonous, and can in fact release the toxins into the surrounding water when they are very stressed! Thus, they do not make good aquarium pets, as they could kill your whole tank of fishes if they release the toxin.

Our hunter-seekers also managed to find us the pretty knobbly sea star (Protoreaster nodosus). This is one of the largest sea star that can be found in local waters, and can grow to about 30cm wide.

We were quite fortunate to see two gigantea carpet anemones (Stichodactyla gigantea) with the ocellaris clownfish! Clownfishes and anemones share an interesting relationship. While most other fishes will be stung by the anemone's stinging cells when they touch its tentacles, the clownfish has a layer of mucus over its body that prevented the anemone from discharging its lethal stings. The fish will help the anemone by luring prey to it, increasing oxygenation, removing waste material, and protect the anemone from some butterflyfishes which feed on the anemone, while the latter helps the fish by giving it protection from predators and leftover food.

We also saw a seahorse (Hippocampus sp.)! Interestingly, male and female seahorses take turns to get pregnant. First, the females will get pregnant with eggs. The males, on the other hand, each has a brood pouch on its tummy. When the eggs are mature, the females will deposit the eggs using an ovipositor into the males' pouches, and eventually the little seahorses will hatch in the pouches.

We also found a stonefish sea cucumber (Actinopyga lecanora). This sea cucumber usually hide among rocks or corals, and when the tide is low, they will harden up and will look and fell just like a piece of rock! Sea cucumbers are made of special tissues called the catch-connective tissues, which allow them to become soft at times to squeeze among rocks and corals, but yet become hard immediately when they felt threatened.

Unfortunately, at the time, we could see the storm clouds moving quickly towards us and had to cut short the walk.

But even as we were heading back to the main road, LK found this cute upside-down jellyfish (Cassiopea sp.). This jellyfish has symbiotic algae, mostly in its tentacles, which photosynthesises better with it being upside-down since they will then be exposed to the sun. Some of the food made by the algae will be transferred to the jellyfish.

Well, so on the whole, even though we can to cut short our programme, it was a great trip with lots of interesting finds! :)

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