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Bibliographies | Behaviour: clams are watching you !
The small giant clam has a quite simple behaviour as it is a sessile organism. However, it exhibits a complex system of eyes all along the mantle edges (Wilkens 1986). Those eyes are clearly seeing changing light intensity, as when you are snorkelling above a clam, it systematically retracts. However, Land (2002) is explaining in his study that clams can see way better than we thought. They are not only sensitive to modifications of light intensity, they can discriminate the black from the white. It is not our shadow that makes them retracting when you go above, it is because you are black compared to the surroundings.
The eye sight of the clam is orientated towards the top as well, and eyes can only see at a certain degree to the left and to the right. Tridacna maxima does not only have a large number of eyes but also it can see at 3 different wavelengths, in the blue, the green and the UV (ultraviolet).
Those eyes are responsible for a complex behaviour of avoiding predation. While exposing the mantle to the sun to make the zooxanthellae of the tubular system harvesting the light, it also exposes itself to the bites of the multiples reef fishes around. And there is the sight coming. When the clams see something coming too close, it just closes a bit its shell, waiting for the danger to move away (Todd 2009).
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