Ascidian Field Trip on Sisters Island

On Tuesday, 18 May 2010, I went to Sisters Island with world ascidian expert, Dr Gretchen Lambert, for a field trip to collect ascidians for the ascidian workshop.


We started off at the mouth of the bigger lagoon, which has several huge colonies of hard corals.


Here's Dr Gretchen Lambert (second from left) showing us the ascidian she found under a dead coral near the reef edge. And of course, all dead corals and rocks that we turned over to look for ascidians were turned back to their original position after we were done with them.


There were certainly lots of ascidians every where under the dead corals and rocks. These chordates start off as free-swimming juveniles which possess a notochord. As the juveniles do not feed, they have to quickly find a suitable spot to settle down to develop into spineless adults. The above is a colonial ascidian.


There were many solitary ascidians too! This one was certainly very well-camouflaged!

Ascidians are found all over the world. They are filter feeders that feed on the plankton in the water that they sucked in using an oral siphon.


Some rocks were practically covered with various species of ascidians!

But as we flipped over rocks to look for ascidians, we also found other interesting stuff.


This tiny sea star not more than 1cm wide was found by Serena under a dead coral near the reef edge.


It looked like an Asterina sp., but the ones (such as Asterina coronata) I had previously seen were never of this colour, and are usually found on rocky shores or seagrass meadows nearer to shore, but never have I found one at the reef edge! It appeared much flatter too.


We also found a few Ovum Cowries (Cypraea ovum) and Dove Snails (will need to confirm the species later).


We found lots of Porcelain Crabs (Petrolisthes sp.) under the rocks and dead corals too.


And once in a while, we get a few brittle stars.


In the shallow pools under the rocks, we found shrimps such as the one above sometimes.


While we spent most of the time looking under rocks and dead corals, we also took note of the animals in the surrounding areas too, such as this Bornella stellifer.


There was this little Funeral Nudibranch (Jorunna funebris) stranded on a little rock too. I quicky place the little rock into a shallow pool next to it, and the nudibranch quickly slid away.


I only saw one flatworm during this trip, which was this Pseudoceros sp.


In the lagoon, I found several small colonies of branching corals (Acropora sp.)


There were a few Giant Carpet Anemones (Stichodactyla gigantea), and I saw clownfishes in some of them. Did not have the time to stop and wait for them to reappear for some photo-taking though.


Out of the lagoons was one of my favourite patch of coral reefs in Singapore! There were so many huge colonies of hard corals and blue corals!


At the rocky shore area, I found a Dolphin Snail (Angaria delphinus).


On the rocky cliff, I spotted a wild Rapanea porteriana! This was my first time seeing such a huge and healthy naturally occuring one!


There were a few Sea Teak (Podocarpus polystachyus) trees too.

All too soon, the tide was rising and we had to go. It was really nice to be back on this island. I certainly look forward to visiting it again later this month for our first public intertidal walk here!