Responses of oysters to turning the flashlight on and off.

<p>1, oyster filtering seawater with a slightly-opened shell prior to switch-on; 2, oyster immediately after switch-on; 3, oyster beginning to open its shells during switch-on; 4, oyster with a wider shell opening during switch-on; 5, oyster beginning to close its shell following switch-off; 6, reduction in size of shell opening following the disappearance of flashlights for several seconds. The ‘switch-on’ indicates the time when the flashlight is switched on; ‘switch-off’ indicates the time when the flashlight is switched off.