[Edit]: Thanks to Ron, there’s more information on the hard coral, squid and the Fiddler Crab’s name is complete now :D
An impromptu invitation by Luan Keng to join the public walk on Sunday led to a great walk with lots of pictures and marine animals seen (: Here it goes!
This tour of the landfill facility on Pulau Semakau saw us sitting for a slideshow presentation and a van ride of the island, passing by the marine transfer centre, the generator building, dumpster trucks that transport waste to the tipping cells that contain the ash, and the southern most tip of the island.
Shortly after the tour, my group (Pufferfish!) was lead by June into the intertidal area, where we stopped by the Sea Lime tree for a taste of some of the riper fruits, and the group had their first encounter of mangrove trees (Rhizophora apiculata).
Right under a bunch of mangrove trees were Fiddler Crabs (Uca annulipes). Male crabs have one large claw (cheliped) that they use in aggressive territorial and courtship behaviour, by waving it up and down intermittently. The burrow seen beside the crab is actually its home.
Sponges (Phylum Porifera) are fairly common in the intertidal area, and they also come in many colours, bright and dull. And if they seem like plants to you, they are actually simple animals! Made up of a few types of cells, they do not have mouths or a digestive system! So how do they eat?
A sponge actually filters water for food, and as the canals in their branching structure narrow, microscopic organic particles, bacteria and plankton get taken up by these cells. Don’t get fooled and touch one though, some sponges can cause irritation – they’re not to be bullied!
We soon came upon the Tape Seagrass (Enhalus acoroides) that is the longest seagrass that can be found in Singapore’s shores – with leaf blades measuring up to 1.5 metres in length! A female flower and male pollen are shown here – male pollen float and raft along, looking like bits of styrofoam, and soon enough catch onto the flowers of the female. Fruits will form soon after.
Almost all sea cucumbers are detrital and/or filter feeders, which means they either feed on microscopic organic material, or plankton. Certain species, once degutted, dried and cleaned, are considered delicacies.
This Snapping shrimp has (unidentified) one enlarged pincer that it uses to create a loud bang (see here for more) that stuns or kills its prey. The actual mechanism involves a jet of water that shoots out from a socket within the pincer, generating a bubble that collapses with a bang as it stabilises, the entire process lasting all of 300 microseconds. The biggest one I’ve seen so far, this one was nearly 10cm long.
The Common Sand Star (Archaster typicus) is, as its name suggests, very common. This is less so today than in the past however, as land reclamation in Singapore has resulted in the loss of the original coastline. Often buried in the sand, a five-armed impression can usually be seen above where they are buried.
Though most seastars are found to be five-armed, it is not unusual to find a four or six-armed seastar as well. Seastars use a water vascular system instead of a blood circulatory system like ours, and hence will dry out and die if they are left out in the sun for too long.
As you can see from the index finger comparison, this is the size of a mature common sand star. Tube feet on the underside of seastars allow them to walk via the water-vascular system as well – and in addition, the common sea star also has spines that allow it to burrow quicker.
Noble Volutes (Cymbiola nobilis) have a beautifully zig-zag patterned shell and black and orange marked body, and this one we saw here is laying eggs. The eggs are translucent, and as can be seen, as big as the noble volute itself. Tiny baby snails will emerge from each egg capsule.
Due to over-collection by people as decorative shell items or even food, this animal is currently listed as ‘Vulnerable‘ in the Red List of Threatened Animals in Singapore.
Seen here from top and bottom views, is the charismatic Heart Cockle (Corculum cardissa), and is part of the family of true cockles. Contrary to popular belief, the Blood Cockle, or ‘See-Hum’ as many locals know it, is not a true cockle, but an Ark Shell (Arcidae).
The shell of this cockle is very thin and flattened out, evolving in such a way that it allows light to penetrate through – giving the zooxanthellae found inside enough sunlight to photosynthesize and produce food for itself. This symbiotic relationship (where both parties benefit) is not a very common relationship found in bivalves.
Moving along, caught and placed into plastic containers for easy viewing were some flatworms! Flatworms (Order Polycladida) are unsegmented worms and can be brilliantly coloured, sometimes seen crawling along the seabed or swimming beautifully with the edges of the flatworm fanning out like a spanish dancer’s dress.
In the top left photograph we have the Red-striped flatworm (Maritigrella virgulata) and the other is the Spotted Black flatworm (Acanthozoon spp.). Flatworms are actually very fragile, and easily tear, and if you look closely, you can see that the edge of the Spotted Black flatworm in this photo is torn off, where the white margin along the periphery of the worm is discontinued.
The Polka-dotted nudibranch (Jorunna funebris) ranges from about 1 – 6cm long, and feeds on sponges (see top) – making it a carnivore! Nudibranches are also incredibly diverse in pattern and colour, and belong to the phylum Mollusca, the same one snails, octopuses and clams are found in!
The name noo-dee-brank means ‘naked gills’, and the gills of this nudibranch have been pointed out here. The rhinophores seen in the picture are used as chemical detectors as they move along in the water – and you can see from the six photos by the side as it moves along.
The Knobbly Seastar (Protoreaster nodosus) is massive for a seastar, and like the Common Seastar featured earlier, uses a water vascular system. This seastar however, is extremely robust due to its heavily calcified body, and this deters predatory fish from eating it.
A popular icon used by Semakau guides, this pretty seastar was also intensely targetted by the marine curio trade for sale and use as a decorative item. Young juvenile knobblies are seldom found, and it is not certain if this is because they mature or reproduce slowly.
And its time or corals! In order of left to right, top then bottom, we have: Dead man’s fingers coral (Soft coral), Sunflower mushroom coral (Heliofungia actiniformis), Omelette coral, Hard coral (Goniopora spp.), Mushroom coral, Zebra coral (Oulastrea crispata).
Soft coral examples are the Dead man’s fingers and Omelette coral, and hard coral examples are the Zebra coral and Mushroom coral.
Corals are usually colonies of animals staying together, and are often explained as a HDB flat housing many animals called polyps, and each polyp creates its own little ‘house’ called a corallite, made of calcium carbonate, beside the other polyps. Above water, they retract back into their corallites for protection and to keep from drying out, but underwater, they come out to feed.
The polyps feed on plankton and microscopic organic material – but some polyps also contain zooxanthellae, single-celled green algae that photosynthesize and share this food with the polyp, that provides it shelter in return.
Free-living corals (not stuck or anchored onto the substrate [rock surface or seabed]) examples are the sunflower mushroom coral and the mushroom coral. This coral is also a solitary polyp, and not a colony of polyps (like the Zebra coral is).
The polyps of this species are considered the largest of all hard corals, and can be mistaken for a sea anemone.
Do take note: It is not recommended that you touch any marine life or corals, as some of them might have stinging cells or may spray out liquid that can irritate the skin. Corals also have a calcerous skeleton that may have spikes or spicules that can be embedded in your skin, causing inflammation or irritation.
The Fluted Giant Clam (Tridacnidae squamosa), is listed as ‘Endangered‘ on the Red List due to extensive over-collection and a rare sight. The wavy flutes, or scutes, that clam creates are used as a ‘platform’ for the clam to extend its fleshy body to face sunlight so the zooxanthellae it harbours can photosynthesize for food.
The Heart Cockle and the Giant Clam are one of the few bivalves that harbour zooxanthellae and receive food from it in this way.
This Tiger tail seahorse (Hippocampus comes) is listed in CITES II, which means its international trade is monitored. Unlike its appearance, the seahorse is a fish, and has bones on the outside as well as the inside. The outside skeleton is inflexible, and acts like armour.
Using fins on its cheek (pectoral) and back (dorsal), it maneuvers around and uses its tail to anchor itself. It does not have a tail or pelvic fin, unlike fishes – thus, they are slow moving creatures, and vulnerable to collectors. Seahorses around the world are endangered.
Spider conches (Lambis lambis) are large snails, and have fantastic camouflage despite their relatively large size and weight. These snails are listed as ‘Vulnerable‘ on the Red List, as local populations dwindle due to over-collection and careless trampling by visitors to the shores.
Conches use their muscular, narrow foot to right themselves if the tides overturn them, and can actually move quite fast. It is also suspected they have eyes that can produce an image (unlike other snails that just differentiate between light and dark)!
Common Hairy Crab (Pilumnus vespertilio) seen here has prickly pointed legs that are used to clutch tightly to rock or coral rubble, and can hurt if picked up like this. This is a male crab, as visible by the pointed (triangular) underside.
A distressed Squid (Sepioteuthis spp.) here has squirted black ink and the black ink cloud is floating beside it.
Sea Hare has cute wings on its back, and have rhinophores like nudibranches. They are, however, very different from them. Sea hares squirt out purple ink if stressed.
The Marine Spider (Desis martensi) is about 1cm in body length, and hides in air pockets among crevices of rocks during high tide, and uses its hairy legs to ‘walk’ on water and hunt for prey.
I could do the mixed photographs either way like this one (numbered) or the previous one (un-numbered). Do feedback on which is better!
June was guiding this group of 11 adults – some other groups had children that looked as young as 7 years old. At the end of the walk, feedback forms were given out and the participants, happy and tired after a long day, started to fall asleep on the ferry back to mainland Singapore.
A good day today! Bright, sunny, and lots of finds today (: My first OJT trip too, excited to start learning even more about these intertidal animals as I can. (: