Jun 20, 2008

Stars at Changi

5am and it's a moonlit night at Changi. And wow, the stars were really out. Not so much in the sky, but on the shores!

The stars were very small but you could still make a guess at their identity if you take a closer look.

The Biscuit star (Goniodiscaster scaber) is quite easy to distinguish with its neatly shaped arms in the form a typical star-shape that we all expect sea stars to be.
A closer look at the upper surface shows lots of little round bumps, some bigger ones in groups.

Here's something that looks like the Biscuit sea star at first glance. It's a juvenile Cake sea star (Anthenea aspera) whose upper surface has tiny pincer-like structures called pedicellariae. They look like tiny clams embedded in the surface and are rather oblong in shape. When this sea star grows up, its arms will get really short compared to its main body (called the central disk) so that the adult looks more like a polygon. In the adult, the central disk also tends to be slightly convex (i.e., rounded). Here's a look at an adult Cake sea star seen at Tuas.

And here's another similar-looking sea star that is probably Gymnanthenea laevis whose upperside has lots of bumps.This sea star is rather rarely seen as an adult and I haven't seen an adult for a long while. But Kok Sheng has seen them recently on Changi this month. As Kok Sheng mentions, when this star grows up, it has really large spines or bumps on the upper surface.

If we look at the shapes of the plates on the edges of the arms, we can also have some ideas on differentiating these three similar looking sea stars.The Biscuit sea star has large neat blocky plates.The Cake sea star has large plates too but they are not so neatly defined.G. laevis has large plates too and to me, these tend to result in a rather scalloped outline.

To differentiate these three sea stars, it's also helpful to have a look at the underside.The Biscuit sea star has a smooth pale underside without bars and stripes or any large pincer-like structures. Most have a typical pattern of blue and orange at the centre, though I've seen some without this pattern.The Cake sea star often has a pattern of darker bars on the arms. It has large pincer-like structures on the underside and each marginal plate (the plates on the edges of the body) also has one large pincer-like structure.G. laevis unfortunately tends to look somewhat similar to the cake sea star. It too has large pincer-like structures on the underside and each marginal plate (the plates on the edges of the body) also has one large pincer-like structure. Sometimes there are also bars on the arms. My impression is that the underside of G. laevis tends to be less smooth and neat than the Cake sea star's. But this is quite hard to judge unless you put the stars next to one another.Here's a closer look at those giant pincer-like structures. Cake sea star in the photo on the left and G. laevis in the photo on the right.

Both the Cake sea star and G. laevis can come in different colours and patterns. So we need to look at small structures to try to figure them out.

There were also other stars on Changi today which are much easier to identify!

This is Nepanthia sp., what I call the Scaly sea star.Because the upper surface does have a texture that resembles scales!The underside can be quite colourful. As you can see it looks very different from the above sea stars in shape and texture of the upper and underside.

And on a nearby rock shore, there were lots of Crown sea stars (Asterina coronata). These sea stars are more commonly seen on rocky shores rather than on seagrass meadows like the above sea stars we saw.Kok Sheng also saw lots of sand stars (Astropecten sp.) today on a more silty portion of the shore. As their common name suggests, sand stars prefer sandier places.

This short stretch of Changi has several different habitats close to one another, and that's why we can see so many different kinds of sea stars in the one hour that we spent on the shore. Kok Sheng saw 8 different sea stars on Changi this month when his team visited during a super low tide!

Alas, we have yet to encounter the Common sea star (Archaster typicus) on Changi. Although I remember the shores being covered with them during my trips as child there (that was a REALLY long time ago, before the shores were affected by reclamation).

These descriptions I've shared is just what I've observed from seeing these stars on many occasions on many of our shores. Do feel free to suggest other field characteristics that can help us distinguish these stars.

But even if we don't know exactly what kind of star it is, we can still appreciate and enjoy meeting them. And note their behaviour and distribution and other field observations. We can share these with experts when they visit. And together we can all learn more about our stars and shores.

Besides sea stars, we also saw lots of other amazing marine life. The shores of Changi are just crowded with animals. Eye-popping pink Thorny sea cucumbers (Colochirus quadrangularis) were everywhere, as well as peacock anemones (Order Ceriantharia) with their attendant black feathery Phoronid worms.
I was so focused on the little red shrimp...That I didn't see the little pipefish just under it!

And I came across this tiny little fugly nudibranch on the sponge encrusted rock. It's possibly Atagema intecta.
Kok Sheng found a Sea apple sea cucumber! Wow! He shares more about the other creatures we encountered, such as a seahorse! More on his wonderful creations blog.

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