First St John's Island Intertidal Walk of the Year

Yesterday, we were off to St John's Island for a guided walk. Kim was my assistant, and our group name was Fiddler Crab.


We started with the sandy lagoon, and almost immediately when we stepped onto the shore, we saw the cast of an Acorn Worm (Class Enteropneusta). This worm feeds by swallowing the sand and process any tiny organic particles from it. The processed sand is push out of its backend, forming the coil of sand.


This was my first time seeing a Pebble Crab (Family Leucosiidae) on St John's Island. This crab burrows very well, and the smooth carapace makes it look just like a polished pebble!


St John's Island is one of those few places left in Singapore that you can still see huge troops of soldier crabs (Dotilla myctiroides).


The biggest surprise of the day must be this Clear Sundial Snail (Architectonica perspectiva) - my first time seeing it! Some more, it's laying eggs!


The sandy lagoon also has several large Haddon's Carpet Anemone (Stichodactyla haddoni). Like other sea anemones, this animal has lots of stinging tentacles which it uses to sting small anemones that got too close to it. The tentacles will then work like a conveyor belt system to bring the prey to the mouth in the middle for it to feed on.


There were lots of Sand-sifting Sea Stars (Archaster typicus) in the lagoon. We were quite lucky to see one with 4 arms, and another with 6 arms. But of course, the most common ones were still the usual ones with 5 arms.


Several Moon Snails (Polinices mammatus) were also spotted in the sandy lagoon. This pretty snail is a fierce predator of small snails and clams! 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 it to feed on the soft body inside.


After exploring the sandy lagoon, we headed towards the rocky shore. Along the way, we saw a Sea Poison Tree (Barringtonia asiatica) with its pretty flower. In the olden days, the seeds of this tree were ground to a powder to stun or kill fish for easy capture. The poison can be destoryed by cooking. Being usually pollinated by moths, it blooms at night, and so we were really lucky that this flower still had not drop off yet.


As we got down onto the rocky shore, we saw a few Land Hermit Crabs (Coenobita cavipes). These hermit crabs are so adapted to life out of water, that they will in fact drown if kept underwater.


The rocky shore usually has lots of animals hidden under the rocks, and we saw a few little purple sea cucumber under one of them.


As we head towards the coral rubble area, we saw this Marine Spider (Desis martensi) scampering over the dead corals. This spider cannot survive underwater too. During high tide, it will trap air with its hairy body, and hide in little crevices. During low tide, it will emerge to hunt for small animals.


There were several huge colonies of Porites Corals (Porites sp.) in sandy areas among the rocky. Most corals look brownish in colour as they harbour a golden-brown algae which can photosynthesizes. Some of the nutrients will be passed to the coral, and in return, metabolic waste from the coral will be passed on to the algae as nutritional supplements.


This pretty snail with intricate patterns is a Spider Conch (Lambis lambis). In some places, they were collected for food and for their pretty shells.


Leaf Slugs (Elysia ornata) are sap-suckers which feed on the Green Hairy Seaweed (Bryopsis sp.). They are able to retain the chloroplast from the sap and use them for photosynthesis!


This is a flatworm, and like its name implies, it is very flat. We usually call this a Persian Carpet Flatworm (Pseudobiceros bedfordi) due to its beautiful patterns on its back.


Huge colonies of Toadstool Leather Coral (Sarcophyton sp.) can be found in tidal pools.


Fan Worms (probably Sabellastarte indica) has lots of tentacles on its head to capture tiny organic particles. The live in a tube, usually made from sand and mucus.


Our hunter-seekers found us a pair of Black Margined glossodoris Nudibranch (Glossodoris atromarginata). The term "nudibranch" means "naked gills", refering to the flower-like gills on the back of most species.


St John's Island has one of my favourite sponge - a Red Maiden's Fan (Oceanapia sagittaria). While this looks like a little flower, it is actually an animal, and feed on plankton and other tiny organic particles.


And here's a group shot of the Fiddler Crabs!

I was really glad that this was, once again, a very successful walk with lots of great finds!