Friday, October 17, 2008

Siloso: seagrass and sea stars


After my first seagrass monitoring session over at Tanjung Rimau, I decided to stay around and explore more of Siloso Beach. The tide was still low enough, and I thought that there more marine life might be out and about after dark. I headed for the bridge that would bring me to one of the islets across the lagoon. And before I had even started to cross the bridge, I found this ghost crab (Ocypode ceratophthalmus). This is the first time I've ever found one on Siloso Beach itself. These crabs are actually quite common on our beaches and sandy shores, but are very shy and come out only at night.

I was hoping that this would be a sign of all the exciting discoveries that lay ahead.

In the shallows, I see shoals of small fish, mostly young Kops' glass perchlet (Ambassis kopsii) and crescent perch (Terapon jarbua). They're too quick for me to even contemplate taking a photograph of them.

Here among the rocks, it looks as if the nerites are out in full force; they're crawling all over the place. I think these are Nerita undata.

Here's a nerite and a sea slater (Ligia sp.) close together.

I've seen reef spiders (Desis sp.) many times on the coral rubble of Tanjung Rimau, but this is the first time I've seen one here in this lagoon. This one seems to have captured some sort of isopod.

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I think this snail is Chicoreus torrefactus, a predator that feeds on bivalves by drilling a small hole into the shell of its prey.

There's zoanthids growing beneath this rock.

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Young halfbeaks (F. Hemirhamphidae) can be seen near the surface.

It's slightly easier to sneak up on mudskippers at night. This one's probably a dusky-gilled mudskipper (Periophthalmus novemradiatus).

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Whelks (Nassarius livescens) are commonly found patrolling the sand, but I wasn't expecting to find a live pearl conch (Laevistrombus canarium).

I've been finding sand collars regularly, but have yet to find any moon snails on this shore. Sand collars are the egg masses of moon snails, and are a mixture of mucus and sand.

Close to the floating bridge, I'm shocked to stumble upon a small patch of spoon seagrass (Halophila ovalis)!

This is the most common species of seagrass found in Singapore, but I'm amazed that it manages to eke out a precarious existence in the murky waters of this lagoon.

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The bridge provides plenty of hiding places for young fish. The one on the left should be a young silver moony (Monodactylus argenteus), but I'm not so sure about the one on the right.

Every time I explore this bridge, I manage to spot purple climber crabs (Metopograpsus sp.).

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Among the rocks on one end of the islet, I discover not one, but two hard corals!

Here's a gang of tidal hermit crabs (Diogenes sp.), inhabiting an assortment of snail shells. I see creeper snails (Batillaria zonalis), three species of whelks (Nassarius livescens, N. crenoliratus and N. pullus), as well as a few drills (F. Muricidae). One way of finding out what snails live in an area is to check out what the hermit crabs are wearing.

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Swimming crabs (Thalamita sp.) and juvenile flower crabs (Portunus pelagicus) are often found in the shallows.

Not often seen though, are moon crabs. I'm not sure if this is the spotted moon crab (Ashtoret lunaris).

Here's another amazing find. A flatworm, swimming away! My expertise in flatworms is lousy, but I guess this could be a species of Pseudobiceros.

I took a short video. Isn't it graceful? These beautiful worms normally crawl around on the seabed, but as you can see, they're also capable of swimming.

Apologies for the video quality; my skills are nowhere close to those of Andy. Almost immediately after I stopped recording, a tiny squid, possibly the same species as the one I found earlier on in the afternoon, swam past. Damn.

But the most exciting discovery of the night overshadows even the flatworm. Last May, I'd found common sea stars (Archaster typicus) in the shallows of this very same islet. You can see my submission of this discovery over on STOMP.

Today, I was hoping to find them again.

The tide is rising, and the water's getting murkier. Just as I'm about to give up, I find one, half-buried in the sand.


Here's another look. It's good to know that there's still at least one common sea star surviving on this shore. I hope there's many more in the deeper parts of the lagoon.

And so, after having spent an entire afternoon and evening on Sentosa, I head for home, exhausted, but absolutely thrilled at all the amazing discoveries I've made today. Who knew that one could find seagrasses, hard corals, flatworms, and sea stars in these seemingly barren swimming lagoons? I'm really keen on exploring Siloso Beach during a really low tide, and see what other treasures I might find.

This is part 2 of a 2-part series on a trip to Siloso Beach on 17th October, 2008.

Part 1: Siloso suntan
Part 2: Siloso: seagrass and sea stars (this post)

Siloso suntan


Today, I returned to Siloso Beach, intent on getting properly tanned after the most recent session was ruined due to rain.

It's quite a soothing experience, chilling out by the beach and napping in the afternoon sun, and admiring beautiful girls walking past. But of course, it gets a little dull after a while, so I also spent some time exploring and looking out for marine life.

The beach is patrolled by numerous birds, among them common mynahs (Acridotheres tristis), Javan mynahs (Acridotheres javanicus) and spotted doves (Streptopelia chinensis), looking for tasty tidbits on the sand.

I noticed something odd about this particular spotted dove. Then I realised that it had no feet! The bird was shuffling around on stumps, but appeared to be in good shape. It didn't have any problems flying. I wonder what sort of unfortunate incident led to it losing its feet.

The sargassum (Sargassum sp.) that choked the beach on the previous visit had largely cleared up, although there were still clumps floating here and there. While I was swimming in the shallows, I came upon a juvenile halfbeak (F. Hemirhamphidae). Naturally, I didn't take any photographs, since I didn't have my camera at hand.

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I found this pretty nerite shell on the beach. I have no idea which species it is; the common nerite species are highly variable, and I still have problems telling the various species apart.

At the end of Siloso Beach, close to where the Naked Hermit Crabs conduct their shore walks, there are these large rocks which form part of a breakwater. These rocks form a hiding place for plenty of marine creatures.

Such as small mudskippers. These are probably dusky-gilled mudskippers (Periophthalmus novemradiatus).

The beach here is also inhabited by sand bubbler crabs (Scopimera sp.).

They're not present in huge numbers, unlike on the islets across the lagoon, but there's still a pretty sizeaable colony.

There are plenty of drills on the rocks. This should be Thais bitubercularis, which is distinguished from its relatives by the presence of spines on its shell. Unfortunately, this species is highly variable, and there are individuals which lack the tubercles on their shells. In such a situation, according to A Guide to Common Seashells of Singapore, the species can 'be distinguished by the shape of the penes'. Well thanks a lot, that was certainly very helpful for identification in the field.

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Tidal hermit crabs (Diogenes sp.) can be found here. The one on the left is wearing the shell of a lightning dove snail (Pictocolumbella ocellata), while the two in the other photo are wearing the shells of a drill (F. Muricidae), and an uncommon member of the top shell family called Euchelus atratus.

Here's a small group of live lightning dove snails.

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This snail is a perfect match for the photos of Drupella concatenata in A Guide to Common Seashells of Singapore. The book states that it's a specialised predator of coral polyps, and that it's often found on Acropora or staghorn coral. Is this a sign that we've got corals growing amongst these rocks? Or maybe there's coral on the outside of the breakwater...

A juvenile halfbeak, the same species as the one I saw while swimming. It's easy to see why they're sometimes mistaken for floating rubbish.

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Some sort of sea aquirt on the left, and the tube of some sort of worm on the right. Switching on the flash and taking photos inside these dark crevices reveals a lot of hidden life.

A tiny squid, just like the one I saw on the previous visit, swims into view, but proves too alert and too skittish to pose for decent photos.

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I realise that the turban snails that I've been finding in these murky swimming lagoons are Turbo intercostalis. This species is also present on the rocky shore and coral rubble at Tanjung Rimau, along with its close relative Turbo bruneus.

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I nearly miss this spotted top shell (Trochus maculatus), with its well-camouflaged shell, but I think my skills at finding these snails have been honed by practice on Tanjung Rimau.

Is this a sponge or a sea squirt?

I think this one's a sponge. I need to brush up on my sessile organisms.

Oh look, a small colony of zoanthids.

I find a mudskipper that's larger than the small ones I saw earlier on. I think it's a gold-spotted mudskipper (Periophthalmus chrysospilos).

High up on the rocks, clustered amongst the acorn barnacles (Balanus sp.), are countless tiny periwinkles (F. Littorinidae).

I had to go wash up and prepare for my first monitoring session with TeamSeagrass. But I knew that if the tide was still low enough after that, I would be back to check out more of Siloso Beach after dark.

Coming up: I explore one of the islets off Siloso Beach at night. What will I discover?

This is part 2 of a 2-part series on a trip to Siloso Beach on 17th October, 2008.

Part 1: Siloso suntan (this post)
Part 2: Siloso: seagrass and sea stars