A Rainy Semakau Walk on 4 April 2010

The sky was overcast when I left home around 5.20am on 4 April 2010. When I reached Marina South Pier, it started raining. To think that it had been bright, sunny and very hot for the past few days, we were indeed a rather unlucky that we should get bad weather when we were going to conduct a Semakau walk!

I was guiding a group of students from Raffles Institution, and my group name was "Seahorse". The students soon arrived, but the rain still had not stopped! We boarded the boat and after about an hour, we reached Semakau.

The rain had stopped then, but only to start again when we reached the entrance to the secondary forest. As a result, we had to wait for about an hour under a shelter until the rain was less heavy and eventually become a little drizzle, and I decided to bring the group to the intertidal area.

Despite the rain, I have to say we were still lucky enough to see many interesting organisms, even though most of them were hiding from the rain!


Here's my group crossing the seagrass meadow. The rain had almost stopped then.


This is a Heart Cockle (Corculum cardissa), and this is definitely one of my favourite clams on Semakau! It got its name from its heart-shaped shell. This cockle can burrow into the sand, and thus it can be rather hard to find them sometimes.


We have been regularly spotting juvenile Cushion Stars (Culcita novaeguineae) for past one year. They appeared to be moving towards the reef edge though. This sea star feeds on corals, and as it grows bigger, the arms will be less obvious and it will look more like a pentagon-shaped cushion instead, hence the common name.


The Green Ceratosoma Nudibranch (Ceratosoma sinuatum) appear to be in season, and we have been seeing them for the past few trips.


This small Black Long-spined Sea Urchin (Diadema setosum) appeared to have been trapped in a tidal pool by the receding tide. They have venomous spines, and thus should not be handled with bare hands.


As usual, the star of the trip is the Knobbly Sea Star (Protoreaster nodosus)! This huge sea star can grow to over 35cm wide, and come in shades of red, orange, brown and beige.


And here's our traditional shot with the knobbly!


At the reef edge, we visited our resident Fluted Giant Clam (Tridacna squamosa). This clam feeds on plankton and tiny organic particles in the water. At the same time, it harbours symbiotic algae in its body. The algae photosynthesizes and pass on some of the food to the clam, and in return gain shelter and protection.


We saw several nudibranchs, and here's another one - a Funeral Nudibranch (Jorunna funebris).

I guess all in all, we were still rather lucky to have seen so many interesting things despite the rain.

One the day before this, we had a survey trip on Semakau too, and we had a scorching sun instead of the rainy weather.

Just to highlight three of the special things we saw:


I found this very pretty sap-sucking slug, a Plakobranchus sp. This is the first time that we saw this on Semakau.


Another new record for the intertidal area of Semakau will be this Forskal's Sidegill Slug (Pleurobranchus forskalii). According to the Nudibranch Encyclopedia, this slug feeds on ascidians.


While we regularly see the Spotted-tail Frogfish (Lophiocharon trisignatus), it was so cute that I decided to still include it here.

It was a great weekend on the whole. Looking forward to find more new things next month... :)

First Intertidal Walk at Pulau Hantu on 2 Apr 2010

This was the very first time we had a guided intertidal walk on Pulau Hantu, and we were really lucky that the weather was fine, despite earlier weather forecast saying that it might rain!

Located to the south of the main island of Singapore, Pulau Hantu actually comprises 2 smaller islands - Pulau Hantu Besar (Big Ghost Island) and Pulau Hantu Kechil (Little Ghost Island). Legend has it that 2 great warriors had a fierce battle at sea, and many people died. The spirit of the sea was very upset with this and intervened, and created a whirlpool that sucked in both warriors. The warriors continued fighting and eventually they killed each other. The gods felt it was wrong for the spirits of the sea to interfere in human affairs, and thus the two dead warriors were transformed into the two islands of Pulau Hantu.

The two islands are now very much reclaimed, but many marine life managed to settled here and hence there are usually lots of interesting things to see here.


There were many elbow crabs (Family Parthenopidae) in the sandy lagoon. They are very well-camouflaged as they trap sediment on their body, allowing them to blend really nicely into the surrounding. They got their name from the shape of their pincers, and the way they usually place them.


We saw a few spider conches (Lambis lambis) too, and a number of dead ones too. This snail has 2 eyes on stalks, allowing it to peep out of its shell to look out for dangers before it starts moving around. It also has a long, sickle-shaped trapdoor, which allows it to hop around like a pole-vaulter.


There were several giant carpet anemone (Stichodactyla gigantea) too. These sea anemones have sticky tentacles which sting small animals that have gotten to close to them. The tentacles will then transport the prey, acting like a conveyor belt system, to bring it to the centre of the animals where the mouth is located.


We saw a few octopuses (Order Octopoda) too! The octopus is said to be one of the smartest invertebrates, and are known to be able to solve puzzles and learn by observation! It is also able to spray a black ink to confuse predators, and change its colours to blend into the surrounding!


The stars of the day must the many red feather stars (Order Comatulida)! We can usually find a few of them on a trip to Pulau Hantu, but I saw like almost 10 of them on this trip! The participants were all quite excited to see these pretty animals, as we don't usually see them on other intertidal walks. Feather stars got their name from the the fact that they appear like balls of feathers, due to their feather-like tentacles. The feather star uses these tentacles to trap plankton and tiny organic matter in the water column for consumption. The mouth is located at the middle of the animal.


There were quite a few magnificent anemones (Heteractis magnifica) too! This is the sea anemone that is featured in the movie "Finding Nemo" as Nemo's home. Unfortunately, we did not find any clownfish among the anemone on this trip.


Instead, I found a stinging nettle jellyfish among the tentacles of one of the magnificent anemones. Guess this unfortunate jellyfish may end up as the food of the anemone.


The stinging nettles (Chrysaora sp.) were in season, and we saw many of them. They were seriously every where! These jellyfish can give rather painful stings, and in fact, a friend of mine unfortunately got stung by one while swimming in one of the lagoons in Sentosa recently.


While we saw a few jellyfish in Pulau Hantu's lagoon, what caught our attention was the many sand-sifting sea stars (Archaster typicus)! This is probably the most common sea star found in Singapore, and can be found on most our southern islands and a few northern shores. This sea star is often wrongly identified as an Astropecten sp., especially in the aquarium trade.


Today was really a nudibranch day, as we saw quiet a few of them! Among them was this funeral nudibranch (Jorunna funebris), which got its name from the black-and-white coloration. "Nudibranch" means "naked gills", refering to the exposed gills on the back of most species.


There was also a black margined glossodoris nudibranch (Glossodoris atromarginata). Its bright yellow and black coloration serves as warning colours to tell predators that it is poisonous. Nudibranchs are basically snails without shells, and they have lost the shell for good reasons, such in the case of this nudibranch, which is poisonous.


I also found this pustulose phyllid nudibranch (Phyllidiella pustulosa) on a rock, and it is also a very poisonous nudibranch.


One of the guides found this Gymnodoris nudibranch (Gymnodoris sp.). This nudibranch feeds on other slugs, and the one above certainly appeared to have eaten something! Being hermaphrodites with both male and female reproductive organs, many nudibranchs fertilise each other while they mate. In the case of Gymnodoris nudibranchs, they often attempt to eat up each other while mating! As such, the one which got eaten will serve as the father and also provide nutrients for the mother and its future generation, while the other will serve as the mother and lay the eggs!

Despite this being the first time we had a guided walk on Pulau Hantu, it was a really great trip with lots of interesting sightings. Thanks to all the participants for being such enthusiastic nature lovers, making this walk such a successful one!