Monday, December 28, 2009

Intertidal sea stars of Singapore

Being a huge sea star fanatic, I felt compelled to blog about these lovely stars in this compilation of most, if not all the known intertidal sea stars that has been sighted in Singapore. It's been a great pleasure to know that so many species of sea stars can be found on our shores: and in this post there are about 20 odd of them!

I will not go into the details of their features and every behaviour but probably just some bits of interesting facts.

The first sea star according to alphabetical order of scientific name is the Cake sea star (Anthenea aspera).

Like different cakes in a bakery, they can come in an assortment of colours and patterns. Probably the most exciting sea star species because you never know the coloration and pattern of the next one you find. Almost all of them were sighted from northern shores. The only time I saw it in the south was in Cyrene Reef.

Though named as the Common sea stars (Archaster typicus), they are no longer as common in mainland just like in the past.

What is probably the most exciting about these stars is their pseudo-copulatory act where the male stacks itself on top of the female interlocking their arms onto their counterpart. Then they will release their eggs and sperms externally. By being in proximal distance, it increases the chances of fertilisation.

The Crown sea star (Asterina coronata) is also known by its common name as the Rock star because they are usually found on the surfaces of the rock. Sometimes they can be also found among the seagrasses and seaweed. They usually come in shades of brown, beige or bright orange.

Well, the Plain sand star (Astropecten indicus) is definitely no stranger to most of us as it is probably one of the most common sea stars one can find in Singapore. Furthermore, they are the subject of my research for a year on their behaviour. I can go on and on describing about these stars but I guess you will have to wait for my papers to be published.

One of the mysteries of this sea star species is that we have not sighted them in the southern shores except for Tanah Merah/East Coast. There is one specimen record in the museum of an Astropecten species found off Semakau but till now, I've not heard any other sighting yet in our Southern waters.

Another Astropecten species that can be found will be this Painted sand star (Astropecten sp.). Their species name has yet to be confirmed as yet. I once suggested it is known as Astropecten vappa but it could be also Astropecten phragmorus.

Compared to its counterpart, this species has painted lines on its aboral upper surface. Their spines by the side of their arms are rather obvious. When handled, they can feel very prickly!

This cool-looking sea star with long tapering arms is the Bordered sea star (Craspidaster hesperus). This is a rare sea star. It's great that I get to catch a sighting of this species twice. First was at Beting Bronok. The second sighting was a total surprise, and that is Tanah Merah, a reclaimed shore!

This sea star that has mottled coloration and patterns is the Cryptic sea star (Cryptasterina sp.). Don't think I need to explain why it's named as the Cryptic star. Most of the time they are found clamping tightly to rock surfaces. An interesting fact of this star is that we have only managed to find it in Pulau Semakau and nowhere else!

Here's the Cushion star (Culcita novaeguineae): the magnificent looking sea star. Indeed being in a shape of a cushion, the ball-like structure and their thick calcified body wall can help fend of predators like fishes from grabbing its appendages or arms and biting them off. Another fact about this star is that they can also eat corals.

However, when the cushion stars are young like this individual, they still have the star shape. It is only when they mature then their shape changes to be more circular.

This sea star is known as the Biscuit sea star (Goniodiscaster scaber). Don't you also think it looks like a biscuit? These stars are also commonly found in the northern intertidal areas. Once in a blue moon, I'll also find them at Cyrene Reef. Well, I'm not surprised as Cyrene is like the Chek Jawa of the south.

The Spiny sea star (Gymnanthenea laevis) is also commonly known as the Orange-tipped sea star. Like the Biscuit sea stars, they are commonly found in the north but for the trips these years, I've seen them to be quite common at East Coast and Tanah Merah as well. Please take note that the orange arms of their arms is not a distinguishing feature of this species.

To know more about the details of identifying them, do refer to the hyperlink (at the name) that will bring you to the Wildfact sheets.

Now over to the three species of the Luidia genus, this one is the Five-armed sea star (Luidia hardwicki). It is rather rare. According to Dr Lane's A guide to sea stars and other echinoderms of Singapore book, they were first recorded from Sultan Shoal and the Pulau Ayer Chawan islands that have since been reclaimed to form Jurong Island. My encounters with them however were all from Changi Beach. Well, Changi is truly an echinoderm heaven.

The other species will be this Eight-armed sand star (Luidia maculata). Having eight arms, they can be very active and are known to hunt for smaller sea stars as part of their diet. They can grow to a giant size and my accidental encounter of a bycatch disposal on the shore revealed that they can probably and easily be the largest sea star in Singapore!

According to the number of Luidia sightings, the Six armed sea star (Luidia penangensis) is the most rare for me. My only time seeing this special star was at Chek Jawa! Ron has seen this species a couple of times at Changi Beach. Though its greyish or beige upper surface is bit boring, you will be stunned by its bright orange tube feets!

Moving on, this pretty little sea star in red is the Scaly sea star (Nepanthia belcheri). Though this one found at Cyrene Reef is six-armed, they are usually five-armed. Most of their sightings are found at seagrasses of northern shores and also Cyrene.

Their upper side is covered with 'scales'. When submerged tiny transparent finger-like structures might be seen on the upperside.

This sea star, the Pentaceraster sea star (Pentaceraster mammilatus), has made it to The Straits Times. First discovered at Cyrene Reef, it was later also nicknamed as the dark evil side of the Knobbly sea star.

This sea star species was previously known to exist only in the western Indian Ocean and the Red Sea, so its presence in Singapore waters represents a considerable range increase. It could be due to Cyrene Reef's location of being in the middle of shipping lane where all sorts of marine larvae could be brought in.

While we all thought that this star was all exclusive to be only found at Cyrene Reef, Ron reported a find of similar looking Pentaceraster sea star at Semakau! Not too sure if it's also the mammilatus species, it is quite clear that it belongs to the Pentaceraster genus.

Well, except for the Icon sea star (Iconaster longimanus) that is found subtidally in our local waters, the intertidal iconic star will be the Knobbly sea stars (Protoreaster nodosus)! They are usually the stars of every guided walk to places like Semakau and Chek Jawa. Nevertheless, they are most abundantly found at Cyrene Reef!

Though prominent and attention seeking, the biology of Knobbly sea stars are not well studied thus far except for Chee Kong's current project that will look further into them. We do not know how they look like when they are very young and this green sea star found at Changi is still a mystery on whether it is a juvenile of the Knobbly sea star or a new species altogether.

To make things more confusing, sometimes we find unknown sea stars that look like a hybrid of the Knobbly sea star with the Pentaceraster sea star. This was sighted at Cyrene Reef.

And this unknown sea star at Semakau looks yet like a hybrid between a Knobbly sea star and a Cushion star. Hahaha.

Well, that's about all my own personal sea star sightings on the intertidal shores of Singapore! Still, there are three more sightings of other species that I've yet to witness with my own eyes.

The first is the Pale scaly sea star (Nepanthia maculata). This sea star was spotted by Ria only once at Beting Bronok. And of course the photo credit goes to her. This is extremely rare and I wish I will be able to have a look in the near future.

Another sea star that I have not seen before is this very recent discovery of the Galloping sand star (Stellaster equestris) by July! (Photo credit to him). It was also probably the first time anyone in Singapore has seen it in the intertidal shores as previous specimens has been only found through dredging.

Unlike most other sea stars which move by gliding across the substrate, this sea star is able to move by jerking or leaping. I can't wait to see this sea star in action before my own eyes. Now to keep my eyes more open whenever I am at Semakau.

Last but not least, the last sea star that I've not seen before will be this orange-looking sea star found at Palau Satumu where the Raffles Lighthouse is. The sighting was reported by Ron at his blog and this photo credit goes back to him as well. We guess it could be rather related to the Crown sea star but till now its identity is still a mystery.

Wow, it has been exciting to have a recap of all the sea stars we have seen on the shores. More photos of my gallery can be found in my flickr set:

May your new 2010 be as starry as the ones we find in Singapore!

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