Jun 3, 2008

Pasir Ris Bliss: Stars!

3am and I'm on Pasir Ris alone. It's my first time on this shore but have heard from Kok Sheng that there's lots of sand stars there. My job this morning is to take photos of them and their measurements. And wow! There sure were lots of sand stars!They came in all kinds of colours, in various sizes,And all kinds of patterns too.Sand stars belong to the genus Astropecten. We're not sure if the one with the pretty patterns on the arms are a different species from the plain ones. It takes close study by scientists to sort out issues of species. So I'm glad Kok Sheng is on top of this question.

The sand star has large flat spines along the sides of the arms. There are also large squarish plates on the sides of the arms.The upperside of the body is covered in tiny patches of bristle-like structures. The white spot is the madreporite; water is sucked into the sea star through this seive-like structure. The mouth is on the underside with grooves along the arms, through which emerge pointed tube feet.

Some of the sand stars had little white snails on them.Even tiny sand stars like this one. Which is why the snails looked relatively large. I believe these are parasitic snails. I'm sure Kok Sheng can tell us more later on. I've seen these snails on the sand stars at Changi as well.

While most sand stars have five arms, there are some with four arms. Elsewhere, I've seen them with six arms too. Here is a four-armed sea star in the little measuring tray that I used to take quick photos of them before returning them.Alas, today, I saw many sand stars with broken off arms. Otherwise, though, they seemed healthy. They did not have 'rotted' wounds or lesions or other signs of disease.

Sea stars can purposely drop off an arm if they feel threatened. This is how they might escape a predator that has chomped on an arm. Or if a stone happens to roll onto an arm.

For this reason, those of us studying stars should NEVER pick up a sea star by the arm. Even big ones like the Knobblies. We should gently lift them by the central disk.After taking their measurements, we should quickly put them back where we found them.

Unless there is a good reason for doing so, it is best not to touch sea stars, especially not to remove them from the water. Taking photos with them out of the water is not a good way to promote care for our shores. Those of us who love our shores should avoid doing this and avoid encouraging people from doing this.

I took measurement of nearly 40 sand stars! I stopped after heeding the protestations of my aged knees and back. So sorry Kok Sheng.

There were also other stars on the shore (which was sprinkled with large rocks), including several Crown sea stars (Asterina coronata).
And I came across one medium sized Cake sea star (Anthenea aspera). How nice to see this star on a rather silty shore.There were also other echinoderms. A few buried ball sea cucumbers (Phyllophorus sp.), and black sea urchins (Temnopleurus sp.). LOTS of black sea urchins!This gathering of very many sea urchins stretched all the way out into the deeper waters!We've seen this sort of gathering of black sea urchins on Changi as well. But it has been a long while since I've come across such a gathering.

The black sea urchin has short black spines. And tends to 'carry' things such as bits of shells, dead leaves, seaweeds and other debris.
Like other sea urchins, the mouth is on the underside. The black sea urchin often has a long banded worm-like thing curled around its mouth. I've seen this several times also on the black sea urchins on Changi.
Quite creepy actually! I have no idea what the worm-like thing is or what its relationship is with the host sea urchin. Yet another mystery that needs more study!

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