The giant clam

Scoica gigant — Giant Clam
Tridacna gigas (L., 1758)

Spread
The giant clam lives in less deep waters of the coral reefs in the south of the Pacific Ocean and the Indian Ocean.

Safeguarding statute: The giant clam is also the most endangered with disappearance from among the marine clams. It figures in IUCN lists with the statute of vulnerable species.

Biology

It is considerably sized, while the adult specimens being able to reach 200 kg and measure around 120 cm in height, their life duration in a natural environment being of 100 years or even longer. In the coral reefs, the clam lives buried in the sand or attached among the calcified corals, at depths of maximum 20 m. Although a widely spread species in the Indian and Pacific area, the populations of Tridacna gigas entered a considerable decline, being disappeared in many areas where it used to be common in the past.

The larva stages of this clam are planktonic, while becoming sesila in the adult stage. The mantle of this clam represents a life friendly environment for algae, with which it lives in symbiosis but which also provides food for it. In day time, the clam opens its valves and exposes its mantle to the sun light, to make possible for the algae to make photosynthesis.

For a very long period of time the clam was considered and named a man-eating clam or the killer clam.

Importance:
It was considered a real danger for divers, while in the diving manuals special techniques to get free are described when the diver could become captive between the clam valves. The giant clam is not considered a danger today, although it is perfectly capable to catch a diver between its valves. The action of valve closing is a purely defensive action and not an aggressive action which takes place very slowly, and for this reason it does not represent a danger. Moreover, there are very many adult individuals that cannot fully close their valves.

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