Recording Kissing Coral Reef

It is pure biology, made visible with the technique of an underwater microscope to record growing reef. As Anthonie van Leeuwenhoek first saw bacteria bring American and Israeli researchers, so the behavior of the polyps of coral in image.

Underwater movies also focused on nature. Just think of the work of Cousteau or Attenborough. It failed, however to date or to record images of the living underwater nature through a microscope, with an accuracy of a micrometer. That’s not easy: get the sharp focus of the living and moving micro-world is tricky, a microscope has usually a very narrow depth of field, while the organisms have a 3D structure, and also the exposure its specific requirements.

Recording Kissing Coral Reef
Photo: The construction of the microscope.

Researchers at the University of California San Diego and by various Israeli institutes designed an underwater microscope suitable for living and moving organisms, the coral polyps, on micrometer scale. Polyps are tiny animals that the living community of the coral shapes and build together the lime skeleton.

The microscope consists lens camera and has led lights for the recording

They use five times the lens that delivers image accuracy of 2.2 µm (1 µm = 1/1000 mm) and has a working distance of 6.5 cm, and can study the polyps that are so from a distance.

Recording Coral Reef
Photo: Combination of several different sharp asked recordings delivers complete depth of field.

To be able to quickly focus the microscope on an electrically adjustable lens. That is a flexible membrane that envelops an optical liquid, where the shape of the lens to change quickly is by using the electric tension that is on it. Can be adjusted within a 1/400 s. With this lens is it possible to always on a different plane of the polyps. Using software to reconstruct the image is then so that the polyp in its entirety in sharp focus.


On the front of the microscope are six led bulbs, which focus on the image to create a smooth light. The leds give light pulses. In this way, motion blur of the polyps, while moving with it post a continuous movie is to reconstruct. The microscope has a digital CCD camera. Lens, leds, flexible lens and camera sitting in one enclosure that when making recordings on a tripod.


Apart of it there is an underwater controller. That contains the batteries for the microscope, good for eight hours of recordings, the control unit for the flashes of light and focusing, and a hard drive to store the data of the camera.

The behavior of the coral polyps was captured during eight hour recording sessions at night in the Gulf of Eilat at a depth of 4m to 8m. Special observations were done: the polyps that are opened to each other to exchange between themselves substances. The authors call that kissing polyps. They also showed aggressive behavior towards other coral species.