Semakau Over Three Days

It was a long but exciting week for me. After the overnight field camp at St John's Island, it was 3 consecutive days of morning trips to Semakau! I had to coordinate and seek for organisms for the first 2 days, and oversee a Project Semakau transect for the 3rd day.


For the first 2 mornings, we had great sunny weathers with spectacular sunrise!


The 3rd day, however, was a rainy day. Fortunately, the rain stopped soon and we were only delayed by 10 minutes or so, and was greeted with a rainbow! It only started raining again when we reached mainland Singapore.

Over the 3 days, many interesting organisms were spotted, and these are just some of the highlights, listed from the simplest to the more complex animals.


Like many of the southern islands of Singapore, Semakau has lots of huge colonies of hard corals. Corals are simple animals with stinging tentacles. Most of them are very small, like the Favid coral (Family Faviidae) above which the individual animals (known as polyps) are no more than 1cm wide. The huge calcium carbonate structure that we see is the coral skeleton. It is like a HDB flat with lots of little occupants.


The Sunflower Mushroom Coral (Heliofungia actiniformis), however, is one huge polyp which lives alone. The above specimen is about 20cm wide. Not only it lives alone, it is also not attached to the substrate and can move around.


There is a huge population of Mushroom Corals (Fungia sp.), but they are usually found nearer to the reef edge, and thus are less often encountered than the Sunflower Mushroom Corals. A juvenile Mushroom Coral is attached to the substrate with a stalk, resembling a mushroom, and thus the common name.


The Cabbage Coral (Trachyphyllia geoffroyi) is one of the less common corals found in Singapore waters.


This is a Tube Anemone (Order Ceriantharia). Though it is very common on our northern shores, I somehow have not seen huge populations on our southern shores.


This Flatworm (Acanthozoon sp.) is very common in local waters, but somehow has not been described yet. Being very flat, it can easily slide into small cracks and gaps among rocks to seek for food and hide from predators. It can also swim by flapping the sides of its body.


This flower-like structure is actually the tentacles of a Fanworm (probably Sabellastarte indica). The body of the worm is hidden in a tube made using sand and mucus. It feeds by using its tentacles to filter for tiny food particles and plankton.


Moving on to my favourite animal group - the echinoderms! We have been quite lucky and saw a couple of juvenile Cushion Stars (Culcita novaeguineae).


Here's the other one. Research has shown that these sea stars feed on corals.


The highlight of every Semakau guided walk is always the Knobbly Sea Stars (Protorester nodosus). I found the above 2 during one of the guided walks.


As usual, there were lots of Knobbly Sea Stars at my transect, and it's just impossible to take photos of everyone of them since I was busy with the transect.


I noticed many Knobbly Sea Stars with missing arms though. Wonder what predator has been chomping on them.


And there were probably hundreds of Sand-sifting Sea Star (Archaster typicus) on the sandy shore of Pulau Semakau.


Several sea cucumber were spotted for the past few days, including this Dragonfish Sea Cucumber (Stichopus horrens). This species is usually not harvested for food as it disintegrates when it was out of water for too long. It is, however, collected to make Air Gamat, a tonic made from the body fluid of sea cucumbers. This sea cucumber also has a rather interesting defense mechanism - it can detach a piece of its skin to distract predators when attacked.


And this is the one most often harvested for food. Called the Sandfish Sea Cucumber (Holothuria scabra), this sea cucumber can burrow into the sand to seek food and escape from predators. It feed on tiny organic particles (aka detritus) found in the sand. They must be properly treated to remove the toxins before they can be consumed though.


This is yet another sea cucumber that is harvested for food, the Stonefish Sea Cucumber (Actinopyga lecanora). It can be found among rocks or dead corals, appearing like a stone sometimes.


Two of the Project Semakau volunteers found this little sea cucumber, which we regularly see but still couldn't get it identified.


The molluscs were quite well-represented on Semakau, and the most attractive ones must be the nudibranchs. The above is a Bohol's Nudibranch (Discodoris boholiensis). It's sometimes mistaken by some to be a flatworm since it is rather flat, but the flower-like gills on its back is a giveaway.


The Black Phyllid Nudibranch (Phyllidiella nigra) is said to be able to secrete toxins to its surrounding when it is stressed.


The Funeral Nudibranch (Jorunna funebris) can be found on Semakau all year round. We have seen it feeding on blue sponges.


The Black Margined Glossodoris Nudibranch (Glossodoris atromarginata) feeds on sponges too.


Our volunteers found this sea slug which we couldn't identify. Guess it's probably a sap-sucking slug.


This resident juvenile Fluted Giant Clam (Tridacna squamosa) is probably only about a few months old!


We have a bigger one nearer to the reef edge, about 40cm wide.


Moving on to the vertebrates, KS's group found this Tigertail Seahorse (Hippocampus comes) quite far away from the reef edge. This is a female seahorse as it lacks the brood pouch which the males possess to hold the eggs. The female seahorse has an ovipositor which it uses to deposit her eggs into the male's pouch, and eventually the little seahorses will hatch inside.


During the transect survey, one of the groups found this cute little Ocellaris Clownfish (Amphiprion ocellaris) which was not camera-shy at all!


One of our volunteers, RH, was more camera-shy though, and he hid his face behind a dried palm leaf he found earlier. Haha...


And I will end this blog with a terrestrial animal - a Black Carpenter Bee (Xylocopa latipes). This is probably the biggest bee species of the world, and can reach a length of 35mm. Carpenter bees can burrow into wood to nest, and thus its common name!