Semakau Over 2 Days in Mar 2011

It always feels good to be back on Semakau :)

We had a guided walk on Friday, followed by a Project Semakau survey on Saturday. The weather was great on Friday, but unfortunately, it rained on Saturday! Luckily, the rain was not heavy, and soon stopped. Hence, we still managed to complete the survey successfully.

Here are some of the organisms we saw on both days:


We had a really lucky trip for the guided walk, as we spotted a number of interesting stuff on our own! The first animal we spotted was this little Mangrove Horseshoe Crab (Carcinoscorpius rotundicauda). Horseshoe crabs are very ancient animals, and are said to have been around for more than 400 million years! They have an interesting way of dealing of bacteria infection - their blood will the bacteria and become gel like. Scientists these days use a substance extracted from the blood to test for bacteria on surgical instruments and also some drugs. And scientists from NUS have developed a way to clone this substance, so that we do not have to harvest from the wild as much.


The second animal we spotted was this Cryptic Rock Star (Cryptasterina sp.). This sea star usually hides under rocks in the day time to escape the heat. So far we have only seen this animals at the few rocky areas on Semakau. This is also the first time that I found this sea star along the guided walk route!


Another sea star we saw during the guided walk, this time round not spotted by us but by an earlier group, was the ever charismatic Knobbly Sea Star (Protoreaster nodosus)! This was just a juvenile, and probably about 10 cm wide. Semakau is one of the few places in Singapore that juvenile Knobbly Sea Stars can be found! And recently, we are seeing quite a number of them! This sea star has a hard calcified body to deter predators from feeding on them.


We did not see the Cushion Star (Culcita novaeguineae) during the guided walk, but saw two of them during the survey!


This is the other Cushion Star we saw. Both are still quite small, about 10 cm wide. This sea star feeds on corals, especially Pocillopora sp. according to studies. They are usually found in coral reefs, but it appears that the juveniles start off in seagrass meadows. Somehow this appears to be the case with the Knobbly Sea Stars as well.


Among the seagrass, we also found many Dragonfish Sea Cucumber (Stichopus horrens). During the survey, I easily saw more than 15 of them! Many of them appeared to be rather short - and it is possible that they have been reproducing by fission. To split into two, each end of a sea cucumber will twist in opposite directions, and the sea cucumber will break into two from the twisting. The lost parts will be regenerated.


There were a few Sandfish Sea Cucumbers (Holothuria scabra) too. This is the species that is usually served in local restaurants. They got their common name from the fact that they are found in sandy habitats, and are able to burrow into the sand.


Also in the seagrass meadow are many Synaptid Sea Cucumbers. This one is probably a Opheodesoma sp. It feeds on tiny decaying particles by picking them up with their lashing tentacles. This sea cucumber is really long, and this one here is definitely more than a metre long.


There were a few Stonefish Sea Cucumbers (Actinopyga lecanora). I usually find them in the coral rubble areas though. They are usually rather smooth and somewhat hard - like a well eroded, smooth rock, which gave it its common name.


The Noble Volute (Cymbiola nobilis) is another commonly seen resident of Semakau's shores. This snail feeds on other snails and clams by wrapping its big foot around them to suffocate them, forcing them to open up so that it can feed on them. We can usually see Noble Volutes of various sizes on Semakau, and sometimes, even those in the process of laying eggs! This is a good indication that they are reproducing well on the island!


A close relative of the snails are the slugs, including the Funeral Nudibranch (Jorunna funebris). "Nudibranch" means "naked gills", refering to the flower-like gills on the back of most species. This nudibranch feeds on sponges.


And one of the favourite food of the Funeral Nudibranch will be this Blue Sponge (Neopetrosia sp.). Sponges are very simple animals with lots of little pores on them. Water is sucked into the animal via these pores, and the sponge will feed on the plankton or other organic particles in the water.


There are many different types of sponges on Semakau, and here's another species - a Spongia sp. Embedded within is sponge are many little clams - Vulsella sp. The openings of these clams form the little slits on the surface of the sponge.


Other clams here are not so well camouflaged though, especially the huge Fluted Giant Clam (Tridacna squamosa). There are myths about divers trapped by the closing valves of giant clams, but they are certainly not true, as the clam closes its valves very slowly, and for many of the bigger ones, they can't even close their shells completely. This giant clam was first spotted about 5 years ago, when it was probably less than 20 cm wide. But now, it is close to 40cm wide!


Not too far away from the giant clam, I spotted this little One-horned Spider Crab (Menaethius monoceros). Just see how well-camouflaged it is. unless it moves, it's really quite difficult to spot this animal.


During the guided walk, we also saw the Gigantic Carpet Anemone (Stichodactyla gigantea), with a pair of Anemone Shrimps (Periclimenes brevicarpalis) on it. The shrimps have a layer of mucous which prevents the sea anemone from stinging them.


Another stinging animal we saw, but during the survey, was this Stinging Nettle (Chrysaora sp.). Seems like they are in season again! The last time I saw them was in May last year.


The surprise find of the survey was this little pipefish, which I have no idea what species it is.


It has lots of little spots on its body. We rarely see pipefishes on Semakau, possible because the seagrass meadows were rather dense and tall.


We also saw another pipefish - the Alligator Pipefish (Syngnathoides biaculeatus). This is a regular find during our fish surveys.


Look at the bits and pieces of little structures on its body - it's no wonder why we seldom see it during our guided walks and other types of surveys. It looks just like the leaf of a tape seagrass with epiphytes growing on it!

I am still taking photos of my old faithful Pentax waterproof camera for my intertidal trips - guess perhaps I should start using my new Nikon 7000 soon :P