Friday, January 16, 2009

Beautiful Tuas

The last time I went to the Tuas intertidal area was more than a year. Thanks to Schering Plough, we were able to make the visit again to check out the shore there on 13 Jan 2009.

Immediately when we walked out to the sandy shore, we saw many sand stars (Astropecten sp.) lying on the reddish sand. These sea stars feed on small seashells, and their presence suggest a good population of seashells too. To feed, they actually swallow the live seashell whole, digest the meat, then spit out the hard shells.

Getting into the shallow waters, the many colonies of soft corals appear before us, spreading out like flowering bushes in an underwater garden. Unfortunately there was a lot of sediment in the water, and thus most of them were covered with a coat of silt.

And in this underwater garden, there were lots of zoanthids too, covering several parts of the shore like floor mats. Sometimes also called colonial anemones, they are related to corals and sea anemones, and possess tentacles with stinging cells to hunt for little microscopic animals or tiny organic particles suspended in the water.

It would have been difficult for us to spot this velcro crab (Camposcia retusa) if it was among the sponges, but unfortunately it was on the sand. This crab plants all kinds of things onto it, dead or alive, such as stones, sponges, ascidians, and algae.

Also a master of camouflage was this spotted-tail frogfish (Lophiocharon trisignatus). By blending so well into its environment, it can hide effectively from its predators, and at the same time, ambush its prey.

It was certainly a pleasant surprise to find this stinging anemone (Family Aliciidae), which I have also seen at Semakau and Changi. It supposedly gives really painful stings.

Interestingly, after sliding around for a while, it started climbing onto a little rock! It stuck its oral disc onto a higher spot on the rock, and then started pulling the entire body column up the rock.

There were several solitary ascidians (Polycarpa sp.) among the coin seaweed (Halimeda sp.). It's rather hard for some to believe that this blob is actually more closely related to us vertebrates than things that can moves a lot like crabs and sea stars. Ascidian are also from the phylum Chordata like us.

Also hiding among the seaweed was this filefish, probably a Monacanthus chinensis.

Several pink thorny sea cucumber (Colochirus quadrangularis) were also spotted. Seems like they were in season at the moment, and we had also seen many them at Changi.

On many of the smooth encrusting sponges, we saw lots of little synaptid sea cucumbers.

One of the really exciting find of the day was this melibe nudibranch (Melibe viridis). Before this we have only seen it on Semakau and Cyrene Reef. This nudibranch supposedly feeds on crustaceans like little crabs and shrimps, but interestingly, we actually saw it being attacked by a hairy crab that night! The hairy crab grabbed it with both claws, like it was hugging it and dragged it into a hole. And all of a suddenly, we saw some mucus-like substances flowing out of the hole! Seems like the nudibranch had released some chemicals. The crab apparently let go, and I was able to get the nudibranch out of the hole with my chopsticks, and it started swimming away by wriggling its long body before settling down a short distance away. This was the first time I actually witness chemical warfare in nudibranchs against a predator! Really exciting!

We also saw a few other more commonly seen nudibranchs, such as this Dendrodoris denisoni.

This bumpy little creature is also a nudibranch, probably a Actinocyclus sp. It was sometimes mistaken to be a marine pulmonate slug (Family Onchididae) due to its bumpy appearance. However, you don't usually find the latter underwater, since it's a pulmonate slug that breathe air with simple lungs, though some species are known to be able to survive for short periods of time underwater by breathing through their skin or gill-like papillae.

Somehow this shore has lots of sponge crabs (Cryptodromia sp.), and we found quite a number of them.

On our way back when the tide was rising, we had another special find - an eight-armed sea star (Luidia maculata)! While this species is rather widely distributed in Singapore, and we have bascially seen it on many of our northern shores, eastern shores, and even southern shores like Pulau Semakau, this was the first time we found it on our western shore!

While Tuas is not exactly a very big area, it certainly has lots of surprises, and I'm certainly keen to visit it again, perhaps on a daytime tide the next time round!

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