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The amazing capabilities of the giant clam.

There are stories from the warmer countries that can make the blood in your veins freeze. Stories about giant clams that can grab the leg of an unsuspecting pearl diver, or even a tourist, and cause death by drowning them.
In fact there are no reported occurrences of this at all, but giant clams do exist, and they have a very interesting lifestyle. This giant is the Tridacna gigas, and can be found mainly in the Pacific, although its most location is the Australian Great Barrier Reef. The size of the clams is quite imposing reaching up to 150 cm, although the largest museum exhibit measured 1368.7 mm. Large specimens can weigh up to 225 kg. The clam has quite a long life span of up to 40 years, and when in season it releases a phenomenal number of eggs – the photo depicts a clam releasing its eggs – there can be a billion in one spawn. (If only we could teach our hens to do the same!) Such egg production in relation to the relatively rare occurrence of the adult is an example of an exceptionally harsh natural selection.

The eating habits of this creature are also very interesting. It is assumed that an important, if not main source of nutrition for the clam, is the unicellular algae Zooanthella, which grows inside the clam itself. In normal conditions, the clam is open and the hinge which joins the two halves of the shell together is anchored in the seabed. Thanks to this, light penetrates to the inside of the clam and photosynthesizing algae living there utilize the light to produce carbohydrates. The  green tinge as is seen in the photograph is an evidence of happy co-operation of these two symbionts. 
This is a great example of symbiosis – the clam gives out plenty of carbon dioxide, which the algae assimilates, it then is eaten by the clam which allows the further excrection of carbon dioxide. Sort of like a snake eating its own tail. Of course the energy source powering all of this is the sun.

[QZC08::034]2,3; [TZE04::160]





© (selected from publications of 
 R. Antoszewski

Titirangi, Auckland, 
New Zeland

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