Semakau Walk on 21 Mar 2010

The last few days had been all rainy days, and thus we were all rather worried that it would rain again today. Fortunately, the weather stayed cloudy, and we had a cool but dry intertidal walk at Semakau instead!

I was the coordinator and seeker again for this trip. Perhaps due to the wet weather for the past few days, we did not find as many things as some of our previous trips, but still, it was a great trip with in fact a rather interesting new sighting!


And the new sighting I was referring to was this huge nudibranch. It's about 20cm long, and definitely the biggest nudibranch I had seen in Singapore so far. Initially I thought it's either a Dendrodoris carbunculosa or a Dendrodoris tuberculosa, but the tubercles (bumps on top) looked simpler, and it has these ridges running by its sides, forming some kind of broken rings around it.


The underside lacks the distinctive white spots found on Dendrodoris tuberculosa, but is also somewhat different from the Dendrodoris carbunculosa I have found on the Net. It's mainly yellow, with a brownish middle and edge. Have dropped a message to the Sea Slug Forum. Hopefully will get a response soon. But even if it is Dendrodoris carbunculosa, it is still a new record for Semakau! We have seen Dendrodoris tuberculosa on a previous trip though. Update: Thanks Budak for the info, this is a Asteronotus cespitosus. Have also gotten a confirmation from Sea Slug Forum.


Another species of nudibranch we saw was the Funeral Nudibranch (Jorunna funebris). Somehow this scene reminds me of Michelangelo's The Creation of Adam.


There were quite a few Dragonfish Sea Cucumbers (Stichopus horrens). This ID is still a tentatively one. Hopefully SY can help confirm the ID soon :P


We saw a few Noble Volutes (Cymbiola nobilis) too, though they were mostly juvenile ones. One of the guides even saw one which was just a few cm long!


At our usual Giant Sea Anemone (Stichodactyla gigantea), we saw a pair of Anemone Shrimps (Periclimenes brevicarpalis). The bigger one is the female, while the smaller one is the male.


We found a few of these little flatworms (Pseudoceros sp.) too.


As usual, the star of the day was the Knobbly Sea Star (Protoreaster nodosus). This huge sea star can still be commonly found on Semakau.


I have lost count of the number of photos I have taken of this Fluted Giant Clam (Tridacna squamosa). It was really huge now, probably close to 40cm across. When we first saw it more than 4 years ago, it was only like about 20cm across.


Compared to the Fluted Giant Clam that was sessile, this other clam, the Heart Cockle (Corculum cardissa), was free-living. Not sure if they were in season, but we had been finding a number of them recently.


One of the groups spotted this Black Long-spined Sea Urchin (Diadema setosum). Have not seen one during a guided walk for quite a while.


This Spider Conch (Lambis lambis) was spotted by another guide while crossing the seagrass meadow. I was looking high and low for it earlier among the seagrass, but couldn't find it. We had been seeing it around the same area recently.

Another thing we noticed recently was the large number of jellyfish. Which can be both rather exciting but scary to look at.


There were quite a number of these Upside-down Jellyfish (Cassiopea sp.). This jellyfish can release stingers into the surrounding water.


There were lots of these hydromedusae, Aequorea sp. This is actually a hydrozoan in the medusa form. Read from the Net that while they do sting, they do not usually cause much discomfort and may even be unnoticeable, except perhaps to those with sensitive skin. However, they were transparent and were almost invisible underwater, and I was a little worried that some students may be stung by it, and basically you won't know who might be allergic to the stings. Fortunately, the guides managed the students rather well, and none of the students waded into deeper water where lots of these jellyfish were floating around.


This other jellyfish, the Stinging Sea Nettle (Chrysaora sp.), was also really abundant today. The smaller ones blended in rather nicely with the seaweed in the surrounding, and this jellyfish supposedly can sting rather painfully.

I was really glad that the guides did a good job today and the students and teachers did not misbehave. Phew.