Monday, October 20, 2008

Seeing Stars on Sisters

For the past few times I went to Sisters Island, I had been hoping to find sea stars there. There was a fairly big and nice patch of spoon seagrass (Halophila ovalis), and the conditions and substrate were very much similar to the sandy lagoons of St John's Island and Pulau Hantu, which both harbour the sand-sifting sea star.

So every time I went to Sisters Island, I faithfully search around the area for any star signs, but in vain. However, this time round, my dreams were fulfilled!

Starfish, Sand-sifting sea star, Archaster typicus
We finally found sand-sifting sea stars (Archaster typicus) on the sandy shore!

It's really hard to describe my joy on seeing the sea stars :)

There were so many of them! And most of them were getting ready for procreation! The one on top is the male. Their reproductive organs do not meet, and they just spray their eggs and sperm into the surrounding water. This interesting reproduction behaviour is known as pseudocopulation, or what I sometimes joke with my fellow volunteers - Fake Sex, But Real Orgasm. Haha... a little R-rated here. Still feeling a bit high after seeing stars on Sisters Island for the first time! :P

moon snail
At the sandy shore, we also encounter a few moon snails, including this pretty little one here. Have no idea what's its ID, but guess SY will probably find out from our mollusc experts soon.

Land hermit crab, Coenobita sp.
JL found several land hermit crabs under a tree. At first glance, I had thought that they were Coenobita cavipes, as I couldn't find some distinctive markings of Coenobita rugosus on their claws. However, on examining my photos again back home, I noticed that it has some other features of Coenobita rugosus. Not sure if I missed the markings while trying to avoid being pinched by the hermit crabs. Guess I'll have to wait for my next trip there to check properly.

Nerites, Nerita sp.
At the rocky shore, we found lots of nerites (Nerita spp.) sliding over the rocks, probably grazing on the algae.

Topshell, Trochus sp.
And nearby on the rocks still cover by water, little top shells (Trochus spp.) wandered.

Turban snail, Turbo sp.
Turban snails (Turbo spp.) were rather abundant too. It's probably easy to guess where their common name comes from by looking at the shape of their shells.

 Marine spider, Desis sp.
There was an algal bloom, and sargassum (a brown seaweed) and bryopsis (a green seaweed) were every where. Among the seaweeds, several little animals were spotted, including the marine spider (Desis sp.) above.

Bigfin reef squid, Sepioteuthis sp.
The squid above was spotted among some sargassum. Previously, I had thought that this could be a cuttelfish as its fins lined the entire length of both sides of its body. However, on checking up on some cephelapod guide, I realised that they were bigfin reef squids (Sepioteuthis sp., probably S. lessoniana) from the family Loliginidae.

Hard coral, Porites sp.
In the big lagoon, lots of hard corals can be found. Some of the colonies, such as the Porites above, can grow really huge.

Anemone coral, Goniopora sp.
Anemone corals (Goniopora spp.) were found in the lagoon too. The long, pretty polyps were swaying with the currents, like they were dancing. If you count carefully, you will realise that the polyps always have 24 tentacles each!

Mushroom coral, Fungia sp.
Several species of mushroom corals are found here, the most common being the free-living, solitary mushroom corals (Fungia spp.).

Gigantic carpet anemone, Stichodactyla gigantea
We spotted this pretty gigantic carpet anemone (Stichodactyla gigantea) near the middle of the lagoon. Update: This is actually a Merten's Carpet Sea Anemone (Stichodactyla mertensii). Thanks to Greg for the correction. Have always thought that this anemone looks different from the usual S. gigantea and thought it could S. mertensii, but had previously thought that the verrucae of the latter would feel sticky. Guess that's not the case. This is what Greg P says: "Verrucae can be adhesive or not, but I don't know that they are ever "sticky" to the touch. I believe that when people refer to adhesive verrucae they are referring to the ability of the verrucae to adhere to the substrate to hold the oral disk open. At any rate, the verrucae on S. mertensii are often very vibrantly colored, and can be the most brightly colored verrucae on any clown anemone. They appear sparse just below the rim of the oral disk, but increase in frequency down the entirety of the column - so that the base of the column is almost entirely covered. S. gigantea, on the other hand, will have verrucae that look almost exactly opposite; they are most frequent just below the rim of the oral disk, and decrease in frequency as you move down the column. There are no verrucae on S. gigantea on the lower half of the column. Additionally, in this photo you can see the checkered pattern of coloration in the tentacles. Only S. haddoni and S. mertensii exhibit this checkered pattern (and only on certain color morphs). You will never see S. gigantea with a checkered pattern."

Ocellaris Clownfish, Amphiprion ocellaris
And swimming among the tentacles were 2 little ocellaris clownfish (Amphiprion ocellaris). The clownfish coat themselves with a layer of mucus produced by the anemone to protect themselves from the stinging tentacles.

Corallimorphs
Several colonies of corallimorphs also made their homes in the big lagoon. They are also call mushroom anemones as they often have a big oral disc with a thin stalk attaching them to the substratum, making them look like little mushrooms. However, these are not true sea anemones, though they are closely related.

Dead man's finger soft coral, Sinularia sp.
Just outside the lagoon, the sargassum cover most things, and most of the time we could only see the bigger animals, such as this dead man's finger soft coral (Sinularia sp.). Imagine if this was submerged in water, the finger-like structures would be swaying in the water, appearing like fingers waving to anyone looking at them. Kind of eerie huh?

Sponges
Sponges were quite abundant just outside the lagoon, but somehow I couldn't find any nudibranchs which feed on them. I guess the sargassum probably hid everything under their long fronds.

Red egg crab, Atergatis integerrimus
While walking back into the lagoon, I came across this red egg crab (Atergatis integerrimus). Note that although it may appear cooked and yummy, this crab is in fact poisonous.

Fish
While searching among the sargassum, I found this pretty fish which I do not know the ID.

Striped eeltail catfish, Plotosus lineatus
Near the mouth of the lagoon, I suddenly saw a "ball" of little critters - juvenile striped eeltail catfish (Plotosus lineatus) - forming interesting shapes as they swam around.

Synaptid sea cucumber
Further back into the lagoon, a synaptid sea cucumber was spotted.

Ribbonworm
And not far from the sea cucumber, a ribbonworm was quietly sliding along on the sandy bed.

Ovum cowrie, Cypraea ovum
We spotted a few ovum cowries (Cypraea ovum) too.

Soon, it was time to go, and I realised that the tide was still quite low. Seemed like the tide table wasn't very accurate this time round, but we had made arrangements with the boatman and the boat was waiting for us.

Wonder when will be the next time I revisit this little island?

6 comments:

neil said...

Ive just looked through your last few posts, some amazing critters youve been finding. A bit more diverse than found here on UK coasts, but then it is a 'little' cold for mangroves here!
Im intrigued by this marine spider. Does it run across the surface capyuring thing that fall into the water or does it actually catch things that come up tot he surface?

tHE tiDE cHAsER said...

Hi Neil, most of the time marine spiders catch things that come up to the surface (like little shrimps, isopods or amphipods), or other little animals that come out to feed when the tide is out, or those stranded on surfaces exposed to the air by the low tide.

When the tide is high, the marine spider will hide in pockets of air in little holes and crevices. It is able to trap some air bubbles with its hairy body too.

Unknown said...

The anemone you have pictured (with the two clowns) is not a S. gigantea, but a S. mertensii. It is unusual to see one in such shallow water - it is normally a deeper water species. The veruccae (spots on the column) are unmistakable and look very different from those of S. gigantea.

tHE tiDE cHAsER said...

Hi, thanks for your comments. Is it possible for you to explain the differences in the verrucae for the 2 species? I remember S. mertensii's supposed to be adhesive, but I remember touching the ones on this particular sea anemone, but they were not. Thanks again.

Greg P said...

Verrucae can be adhesive or not, but I don't know that they are ever "sticky" to the touch. I believe that when people refer to adhesive verrucae they are referring to the ability of the verrucae to adhere to the substrate to hold the oral disk open. At any rate, the verrucae on S. mertensii are often very vibrantly colored, and can be the most brightly colored verrucae on any clown anemone. They appear sparse just below the rim of the oral disk, but increase in frequency down the entirety of the column - so that the base of the column is almost entirely covered. S. gigantea, on the other hand, will have verrucae that look almost exactly opposite; they are most frequent just below the rim of the oral disk, and decrease in frequency as you move down the column. There are no verrucae on S. gigantea on the lower half of the column. Additionally, in this photo you can see the checkered pattern of coloration in the tentacles. Only S. haddoni and S. mertensii exhibit this checkered pattern (and only on certain color morphs). You will never see S. gigantea with a checkered pattern.

I wish I could post photos :) You have an amazing site, by the way!!

tHE tiDE cHAsER said...

Thanks so much for the information! Perhaps you can email me sample photos at ronyeo@gmail.com. Thanks again!