Sunday, June 7, 2009

Burrowing giant clam at Hantu

I was out with the RMBR guides at Pulau Hantu at a super early 2.45am trip and one of my personal objectives is to find the giant clam(s) which I failed to find in all my previous Hantu trips.

And when I was already giving up (probably given up hope) towards the end, Eunice called out to me of her clammy find!

Wow, this is a Burrowing Giant Clam (Tridacna crocea)! Tridacna crocea also has many other common names, including the boring clam, crocus clam, crocea clam or saffron-coloured clam.

This species can burrow into rocks or corals by using their ridges of its thick shell to dig into the substrate by opening and closing quickly through the use of its byssal muscles. At 10-15cm, it is the smallest of the giant clams. Therefore, their burrowing behavior can help this small giant clam species to protect itself from predators such as sea stars and butterflyfishes.

The Burrowing Giant Clam relies heavily on the photosynthesis of the algae growing in its mantle which is brown in colour. They seem to have wavy 'lips' at the opening edge of the bivalve shell where the mantle lies.

Giant clams are known to have eye-spots at the edge of its mantle but I am not too sure if the brown dots here are the eye-spots. Maybe Mei Lin can help me clarify this.

Giant clams have often been overfished and the burrowing giant clam is listed among the threatened animals of Singapore, due to over-collection. This partly explains why we do not see them often in our shores on top of probably they are well camouflaged out of water. This is only my second time seeing this species in the wild. My first was at Raffles Lighthouse last year.

More Hantu-ey finds of the day to be posted soon when I catch up with my lost sleeps and time. Watch out for this space!


Anonymous said...

Yes the black dots are their eyes. They can have them throughout their mantle but they are most common at the outer edge.

Crocea and maxima clams borough into the rock actually by dissolving the rock, not grinding it away. They have a flap of tissue they extend from the byssal opening called the pedal mantle. The pedal mantle can extend all the way up to the top of their shell, and the clam secretes a weak acid that dissolves calcium carbonate material. These same acids can come from the upper mantle also as you can see in this photo where the upper mantle has dissolved the surrounding rock.


Unknown said...

Thanks Chris for sharing so much about the clams!! :)

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