Semakau Walk with Tampines Secondary School

This was the third day in a row for me going to Semakau, but unlike the previous 2 days which I was here for Project Semakau's hunting-seeking survey, I was guiding a group of students from Tampines Secondary School today, also part of Project Semakau's effort to share the island's interesting marine life with students.


The Acorn Worms (Class Enteropneusta) were back with a vengeance! For quite a while, we had not been seeing many of them on the sandflat, but they seemed to be coming back, in full force! I saw so many of them today that I lost count of them. This animal swallows sand or mud to digest the organic matter inside, and the processed sand or mud will be excreted on the surface, somewhat coiled up like above.


Fan Shells (Family Pinnidae) are very common Semakau among the seagrass. This huge bivalve is edible, and is collected for food in the region. It is a filter-feeder, meaning that it filters for tiny organic particles or plankton from the water to feed on.


Here's the traditional shot of my group crossing the seagrass meadow :)

We have a fixed route that we took every time we cross the seagrass meadow to minimise damage to the surrounding habitat.


And here's a more wacky one. Haha!


Our hunter-seekers found us this Smooth Spooner (Etisus laevimanus). The tip of its pincers were flat like little spoons, allowing it to scrape algae off rocks to feed on.


Several Sentinel Crabs (Macrophthalmus sp.) were spotted after we crossed the seagrass meadow. These crabs have long eye stalks to allow them to have a good view of the surrounding to watch out for predators.


The resident Giant Carpet Anemone (Stichodactyla gigantea) was right at the same spot. Like other sea anemones, it has lots of stinging tentacles to sting and capture small animals which got too close to it. The tentacles will then transfer the prey to the mouth located in the middle.


Near the anemone was a little Ovum Cowrie (Cypraea ovum). This snail has a very smooth shell, which it protects from scratches with its mantle. The mantle also allows it to camouflage into the surrounding. This cowrie feeds on algae.


Our hunter-seekers found us this little Fluted Giant Clam (Tridacna squamosa). Sounds strange to call it a little giant :P. It is actually a juvenile, hardly more than 8cm long!


The adult Fluted Giant Clam looks like this. I was really glad to find this clam still at the same spot. Being an edible clam, it is often collected in the nearby countries for food. This is one of the largest clams in the world, being able to grow to about 40cm long, and this particular individual is almost there!


It has been a while since we last saw a Black Long-spined Sea Urchin (Diadema setosum) at the intertidal area of Pulau Semakau. The needle-like long spines are very brittle and have a mild venom, which can cause swelling and pain if you are pricked by them.


Once again, we found the unidentified sea star which was first sighted during the launch of Project Semakau. It seemed to be slightly bigger though. I must remember to measure it the next time I see it...

Sea stars, sea cucumbers and sea urchins are actually related, being from the same phylum Echinodermata.


Fanworms (probably Sabellastarte indica) were rather abundant, and one or two can be found in most tidal pools. They are also filter-feeders, and feed by creating a little current with their tentacles and pick up plankton or tiny organic particles to feed on.


I found this small Flatworm (Pseudoceros sp.) in a tidal pool. Being so flat, it is able to slide into narrow cracks among rocks to hunt for food or hide from predators.


On almost all our trips to Semakau in recent years, we have been finding Noble Volutes (Cymbiola nobilis) laying eggs - a very good sign indicating that these snails were doing well! This snail is a fierce predator of clams and other smaller snails. It will embrace its prey with its huge foot to attempt to suffocate it. When the prey eventually open up to breathe, the volute will feed on it.


Sometimes mistaken to be sea anemones, the Anemone Coral (Goniopora sp.) is actually a hard coral with a hard calcium carbonate skeleton.


This one is a soft coral though, which has a fleshy skeleton. Looks like a Capnella sp. to me, but can't say for sure since I am not soft coral expert. Haha.


The Funeral Nudibranch (Jorunna funebris) is a common sea slug found on Semakau. The term "nudibranch" means "naked gills", refering to the exposed flower-like gills on the back of most species.


The Green Ceratosoma Nudibranch (Ceratosoma sinuatum) is seasonally common though, and we usually see it just a few times a year.


I was rather excited to find this Granulated Flatfoot (Platypodia granulosa). This crab is believed to be the second most poisonous crab in Singapore!


And I noticed that this one was a mama that was pregnant! Looks at the eggs it was holding under its abdomen.


And again, we found another Noble Volute which had just finished laying its eggs.


The star of most Semakau guide walks must be this - the Knobbly Sea Stars (Protoreaster nodosus)! This is one of the biggest sea star in Singapore, and can grow to about 30cm wide. One interesting fact about sea stars is that they are actually brainless! Yet, they survive very well!


Here's a group shot with our stars of the day!


Heading back to the seagrass meadow, I found another Giant Carpet Anemone which had a pair of Anemone Shrimps (Periclimenes brevicarpalis). The shrimps scavenge for food among the anemone's tentacles, but when food is scarce, they may feed on the anemone’s tentacles! They protect themselves from the anemone’s stinging cells by coating their body with the mucus secreted by the anemone.


We also found a Sandfish Sea Cucumber (Holothuria scabra). This is the sea cucumber that you get in Chinese restaurants, but they must be properly treated to remove the toxins before they can be consumed. This sea cucumber got its name from the fact that they live in sandy substrate, and is able to burrow into the sand.


Another sea cucumber we saw was this Synaptid Sea Cucumber (Family Synaptidae). It feed on tiny organic particles by lashing its tentacles around to pick them up from its surrounding. This is probably the longest sea cucumber species in Singapore, and I have seen those reaching about 2m long.


Sand-sifting Sea Stars (Archaster typicus) were very common on Semakau, and on some trips we could find hundreds of them! They can burrow, and feed on tiny organic particles on the sand.


We found this Dragonfish Sea Cucumber (Stichopus horrens) near the seagrass meadow on our way back. Sea cucumbers from this group get very limp, looking like they were melting, when removed from water for too long. In fact, they may eventually disintegrate all together, unless they were return to water soon enough to reverse this process and recover.


As a we were about to head out of the intertidal area, we had a surprise visit by a cute little Soldier Crab (Dotilla myctiroides). On some of our shores, we could find hundreds of these crabs moving together, like a troop of army soldiers! Unfortunately, this crab we saw appeared to be in a one-crab-army though.

All in all, it was a good trip and I hope all the students enjoyed it! :)