08 February 2009

Stars and hearts on Pulau Semakau

What a fantastic day out with TeamSeagrass yesterday! After completing the monitoring, the team had a quick look around and came back with stories of many interesting encounters.
I seemed to have stumbled on the 'hot spot' of Knobbly sea stars (Protoreaster nodosus) on Pulau Semakau! These stars are not as commonly seen as on Cyrene Reef, but yesterday, I came across six of them in a small area. This large one in the photo above was curled up as they usually do when exposed out of water. I'm still not sure why they do this.

It was particularly nice to see lots of smaller ones too!
Like this pale one with small knobs.
Another pale one with larger knobs.
A brownish one.A more typical reddish one.Alas, one with an arm that seems to have got chomped off. Sea stars do grow back their arms, so I'm sure this little one will be alright after a while.

Sam also spotted the special sea star that was seen by other shore visitors.

Always a special find is the Heart cockle (Corculum cardissa).
This heart-shaped clam with the opening of the valves down the centre of the 'heart'. One half of the valve is flat (photo above) while the other is convex (photo below).Pulau Semakau is one of the few shores where this special clam is seen relatively regularly.I also came across this odd bivalve with fine beads on the ridges of its shell. I have no idea what it is.

Having learnt about the Hammer oyster (Malleus sp.) on Cyrene Reef, I was on the look out for this strange clam on Pulau Semakau as well.There were these odd shaped thin shelled animals that look like tongue depressors attached to small stones near the reefs.Here's what they look like on the underside. Could they be Hammer oysters too? Still so much to find out about our shores!I didn't see any nudibranchs except this really small little Ceratosoma nudibranch (Ceratosoma sp.). But after the walk, Timothy showed us photos of a huge Platydoris scabra that he saw.

I finally spotted the little heart urchin that was encountered by many other visitors to this shore. The second 'heart' creature after the Heart cockle! It's really cute and small with a very obvious petalloid. It looks a lot like the Maretia planulata in Dr David Lane's "Guide to Sea Stars and Other Echinoderms of Singapore". The photo of the living animal in the guidebook is from Pulau Bintan. But according to the guidebook, the animal has been collected subtidally at Pulau Semakau by dredging. The mouth is on the underside, and it has long sparse spines. This animal burrows in the sand, and this is what it looked like when I first saw it.There's a depression in the little mound of sand that is the same shape as the heart urchin. Perhaps the poor little creature unexpectedly popped out of the sand mound when it was burrowing! It seemed much happier in the pool of water that I placed it in.

Marcus found another heart urchin that was pink! See his photo on his flickr.

Pulau Semakau also has other interesting echinoderms.I saw several humungous and active bobbly big synaptid sea cucumbers.There was also this small Grey thorny long sea cucumber tucked near a rock. Siti and the other TeamSeagrass folks saw the HUMUNGOUS Eye-spotted sea cucumber (Stichopus ocellatus) that we saw during an earlier trip to Semakau. This encounter caused quite a ruckus!

While waiting for the others to gather at the end of the day, I looked closely at the seagrasss and saw these things.I'm not sure if they are sea anemones or something else altogether. I also saw Giant carpet anemones (Stichodactyla gigantea) but no 'Nemos'. But some others from the Team saw these fishes.

The rest, however, saw more interesting cnidarians. Alvin saw an Upside down jellyfish (Cassiopea sp.), while Ivan saw what seems to be yet another Heteractis crispa, a large but rarely seen sea anemone. Marcus found one during an earlier visit.

The most amazing encounter of the day must be the 90cm-long mackerel that Andy and Alvin saw in their seagrass monitoring site! Alvin has photos to prove its size as they used the transect tape in the photograph! It was very much alive and was in a deep pool of water, probably prevented from leaving the shore at low tide by the driftnet stretched over the shores. Andy later released it into deeper water. [Afternote: Eric Leong, after viewing the photo of the fish, says its a Queenfish and not a mackerel.]

I'm sure we'll hear more about these encounters in upcoming blog entries.

More about this trip

1 comment:

  1. Probably the knobblies curl up out of water to reduce surface area in order to minimize dessication? :-)



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