Saturday, May 30, 2009

My first St John's intertidal guided walk

It has been some time since I've visited the Tanjong Hakim shore of St John's Island. This time, I am visiting it with a group of new friends through my first St John's Island guiding of the intertidal area.


It was a scorching bright sunny morning and we first headed out to the sandy lagoon.


And these are the friends I was referring to. A group of friendly and interesting people who are very interested in the marine life of Singapore. Melissa (in yellow) was formerly a marine biologist!

We began the walk from the high shore to the lower shore zonation.


And within the sandy lagoon, we realized that it is home to many Common sea star (Archaster typicus)! And we witnessed stars with even four and six arms!

Interesting facts about this starfish species are that it can eject its stomach to feed and that they have the ability to regenerate their arm if there is a sublethal arm loss which can be caused by predation.


There were quite a number of small crab finds including the Pebble crab (Family Leucosiidae) on the left and the Soldier crab (Dotilla sp.). In addition, there are also several Sand bubbler crabs (Scopimera sp.) and Orange fiddler crabs (Uca vocans).


A pair of the Oval moon snails (Polinices mammatus) was also found by our hunter seekers.

Moon snails are fierce predators, feeding on bivalves and snails. A moon snail wraps its huge body around the hapless prey to suffocate it. If this fails, it has a gland at the tip of its proboscis that secretes an acid to soften the victim's shell. With some help from its radula, a hole is created.


After looking at the special find of the Sundial snail, some anemone-looking tentacles were found nearby. Could this be a juvenile Bulb-tentacled sea anemone (Entacmaea quadricolor)?


I later went on to talk about our natural oysters. Oysters are well known to be delicacies in seafood. However, people also associate them with beautiful pearls and may try to pry them open to find them in the wild. However, these pearls are generally not found in nature.

Most pearls we see in the market are cultured and produced on farms. A plastic bead is inserted under stringent conditions, into special bivalves and removed when a thin layer of mother-of-pearl is secreted by the animal. Natural pearls tend to be mishappen and worthless and only occur when a bit of dirt accidentally enters the oyster, which doesn't happen often. Therefore, please don't needlessly kill wild oysters out of curiosity.


The next part of our walk is down to the natural coral fringing reef. The tide looks low!


Before we proceeded to the lower shore, there was a Land hermit crab (Coenobita sp.) found very high up. If you are wondering why, it is because the land hermit crab is so well adapted to life out of water that it will drown if kept underwater! It has special gill chambers that act as lungs.

We went on to talk about how these land hermit crabs are being sold in shopping centres as pets at high prices. This is definitely one of the many threats including that these poor hermits have to endure. For me, I love to see animals happy living in their natural homes. Who likes to be jailed? Do you? Animals, as living creatures like humans, also have the right to live where they originally belong to.


Most people have the impression that seaweed is not in the tube shaped form but this White-stemmed seaweed (Neomeris sp.) is indeed a seaweed. Clusters of these seaweed are usually found on rocks and coral rubble.


A Fireband murex snail (Chicoreus torrefactus) was also sighted! Like the moon snail it can soften the shell of its victim with a weak acid secreted by a special gland on the underside of its foot. Elsewhere, this snail is frequently collected for food and shellcraft. In some localities, populations have been greatly reduced because of over collecting.


The spider conch (Lambis lambis) is definitely an interesting animal! Not only is its pattern being pretty, this conch has two long eye stalks that can peer at all of us. In additon, it has a long muscular foot that can flip itself back and we were marvelled at how it does this!


Of course, coral reefs of the St John's definitely has hard corals like this Pore coral (Porites sp.) that is commonly found here.

Another common coral of this shore will be the Blue coral (Heliopora coerulea). But the blue coral is more related to soft corals instead.


Soft corals of St John's include this creepy looking soft coral that we named as the Dead man's finger. Indeed, it looks like many dead men fingers are coming out from the rock. They look bizzare!


More soft corals abound at the deeper waters.

Sadly, our impression of St John's shore seems to be that the hard corals are doing poorly as compared to the past. Could it be due to the landslides? I reckon it be due to the change in hydrodynamics after the bridge that links to Lazarus has been built. Hydrodynamics of the sea is very important in both providing nutrients to the corals and also provide spawnings of new corals from reef sources elsewhere.


There were a number of flatworms to us to see thanks to the hardwork of our hunter seekers!
The Persian carpet flatworm (Pseudobiceros bedfordi) is one that can eat ascidians and other small crustaceans.


Other flatworms include the Orange-edged black flatworm (Pseudobiceros uniarborensis) on the left and the electrifying blue-in-colour yet rarely seen Red-tipped flatworm (Pseudoceros bifurcus)!

Though the rocky shore may look lifeless, most living creatures are actually hiding beneath rocks to prevent dessication and heat stress. So I overturned some rocks to show how life teems at the underside of the rock without themselves being squashed.


Aha, first we saw a Beige flatworm that sort of resembles mobile phlegm. :P


Then there were also creatures like a sponge, a sea cucumber, snails, small clams and ascidians clinging onto the underside of the rock. We later saw lots of Purple under-a-stone sea cucumbers under a particular rock! It was most fascinating.


How come there seems to be an aerial photograph of many volcanoes?

No lah, it is actually a normal photo of lots of Volcano barnacles (Tetraclita sp.) covered in green algae. But it is such a lovely piece of natural art, don't you agree with me too?


Before we left the rocky shore at the end of the walk, we took another group photo. Take nothing but photographs, leave nothing but footprints.

Thank you my group "Mangroves" for being such a nice group to share the marine life of St John's with.


Parts of St John's natural rocky shores are as charming as before. Such coastal landforms are now rare in Singapore.

However, it was sad to see huge portions of the cliff being cemented to prevent further landslides. I didn't have the heart to show you all the cemented cliff photo but landslides are usually caused by human modifications of the biophysical conditions, which is existing at St John's higher up above the cliffs.

Thus, it is crucial that development of all sorts should be done in due respect and knowledge of how nature works. If done sensitively, development and conservation of nature can coexist just like Semakau landfill. I'm not too sure if it applies to St John's as well given so many threats it is currently facing.

2 comments:

APRIL LORIER said...

I've never seen flat worms before. They are profoundly interesting! And I never knew how pearls were "manufactured", either. This was a very informative article! Isn't God's creation awesome?

April from ChristianNature Blog

koksheng said...

Hi April! Glad to hear from you that you like the article about God's wonderful creation :)

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