Semakau on 1 Oct

A rather late entry again :P

Went to Semakau on 1 Oct, which so happened to be both Children's Day and Hari Raya Puasa as well. I was the hunter-seeker for the day, so didn't have to guide any visitors.

Here are some of the things we saw during the trip.


The lonely bakau tree (probably Rhizophora stylosa) near the entrance to the secondary forest. I've been to Semakau so many times, but this was the first time that I actually took a photo of the entire tree :P


As usual, the shallow tidal pools in the sandy area had lots of tidal hermit crabs (Diogenes sp.). These hermit crabs are scavengers with a good sense of smell.


The gong gong (Laevistrombus canarium) is also quite common, but is usually rather well camouflaged, unless you turn it over...


Semakau has one of the largest seagrass meadow in Singapore. With lots of food and hiding places, this habitat attracts lots of animals, many of which use it as a breeding ground and also nursery ground for their next generation.


One of the animals that we can usually find among the seagrasses is this long synaptid sea cucumber (Family Synaptidae), which can grow to about 3m! They feed on tiny organic particles which they pick up by lashing their oral tentacles around the surrounding seagrass and substrate.


On this special day, we had a surprise visit from a file snake (Acrochordus granulatus) in the seagrass meadow! This was the first time I saw a file snake in the seagrass meadows - the previous 3 times I saw file snakes on Semakau were either at the reef crest or coral rubble area. Strangely, the file snakes I've seen in Semakau all had a layer of algae over their skins. The only time I saw one without the layer of algae and showing its banded patterns was a dead one at the coral rubble.


Among the seagrasses, I found this sandfish sea cucumber (Holothuria scabra). This is usually the one you find in Chinese restaurants, but they must be properly processed to remove the toxins in them before they can be eaten.


At the coral rubble area, I also found this dragonfish sea cucumber (Stichopus horrens). This sea cucumber gets very stress out if it's out of water for too long, and may in fact "melt" and disintegrate. This process may be reversed if the sea cucumber is not too far gone and returned to water though.


Can't remember whether it was LK or ST who found this little noble volute (Cymbiola nobilis). We have been seeing many noble volutes for the past few months. These snails are hunters of other shells.


ST found a little wandering cowrie (Cypraea errones). This snail has a very smooth and glossy shell, protected from abrasion by its mantle, which usually extends over the shell. It feeds on algae.


LK soon found this stonefish sea cucumber (Actinopyga lecanora).


It didn't take long for ST to find a knobbly sea star (Protoreaster nodosus), and I soon found another one. They got their common name from the many knobs on the upper side.


He also found this spider conch (Lambis lambis) which has a little colony of coral on its shell!


There are many scallops in the various tidal pools if you take a closer look.


The tide was quite low and we managed to have a good view of the fluted giant clam (Tridacna squamosa). This clam can grow to about 40cm long. It is a filter feeder which feeds on plankton and other organic particles in the water, but gets a portion of its nutritional requirement from the algae that live inside it too. The algae, also known as zooxanthellae, can photosynthesise and pass on some of the food to the clam.


Semakau is one of the best places in Singapore to see a large variety of hard corals. I was rather disturbed when I saw the anemone coral (Goniopora sp.) above though - it's bleaching. Hard corals bleach when they lose the zooxanthellae in them, since most of the time they get their brownish colour from the algae. Losing the algae will mean that the corals will be losing their main source of nutrition as well, since they get much of their food from the algae. If they couldn't recruit new zooxanthellae in time, these bleach corals may eventually die.


Semakau is a great place to see soft corals too. This flowery soft coral (could be Dendronephtya sp.) is quite commonly found in tidal pools here.


I managed to find the pair of tigertail seahorses (Hippocampus comes) at the usual spot again! I almost gave up finding them after searching in vain for quite a while. Glad that I found them just before I wanted to give up. The above is one of them. ST and LK later also found another seahorse in another part of the reef crest.


We managed to find a few nudibranchs too, including the Glossodoris nudibranch (Glossodoris atromarginata) above. The word "nudibranch" means "naked gills", refering to the flower-like gills found on the back of most species.


Another nudibranch we found was this funeral nudibranch (Jorunna funebris), which got its common name from the black-and-white coloration. We sometimes also call it the polka dot nudibranch.


Several flatworms were spotted in various tidal pools and also at the reef crest. The above is probably an Acanthozoon flatworm (Acanthozoon sp.). Flatworms are very flat, which allows them to easily slip into narrow crevices to seek for food and also to hide from their predators.


I saw a few very pretty red maiden's fan sponges (Oceanapia sagittaria) near the reef crest too. While they look like pretty little red flowers, they are in fact animals, not plants! Sponges are mostly filter feeders, and they suck in water through tiny pores on their body and pick out plankton or little organic particles to feed on. The processed water will then be ejected from big holes.


It was already quite dark on our way back, and I had to be really careful so as not to step on any of these sand sifting sea stars (Archaster typicus). One of the pairs in the photo above were getting ready for procreation. The male was on top of the female, holding the latter in position while waiting for the tide to rise. After which, they will spray the eggs and sperm into the water. As their reproductive organs do not really meet, this behaviour is called pseudocopulation.

All in all, it was again another great trip. The best part must be the file snake though. It was so graceful when it was swimming among the seagrasses!

Sure hope to see it again next time :P