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Experimental set-up with a cut coral porites placed on top of a transparent planar oxygen optode, which was fixed at the bottom of a glass container, filled with lagoon sea water. The blue light is the excitation light, coming from blue LEDs arranged in a frame below the glass. While the orange-red light corresponds to the excited luminescence of the optode. The fixed white tube (upper right part) served for flushing the water surface with a constant air stream to aerate the water.

The optical measurement of oxygen is based on the ability of certain dyes or luminophores to change their optical properties corresponding to a change of concentration of the analyte – oxygen. These indicators can be incorporated in polymers and easily spread on transparent support foils allowing the 2D measurement of oxygen and the "look through". With a special measuring system, called modular luminescence lifetime imaging system (MOLLI) it is possible to use the "delayed" luminescence for the oxygen measurement and white light illumination for structural images. The use of the decaying luminescence (light emitted when the excitation light source is switched off) is possible with a special CCD camera with a fast electronical shutter and additional modulation input (sensicam sensimod), if the luminescence decay times are in the range of µs or larger.

Measured 2D oxygen distribution (view to cut coral surface) given in % air saturation. The oxygen image is blended into a black&white image from the coral structure. The high oxygen values were generated by endolothic cells, which live within the coral skeleton. The production was triggered, by a weak illumination through the oxygen sensor, which simulated the normal light situation of these cells at daylight in the reef.

In the presented application, the light dependent metabolism of endolithic cells, which live within the skeleton of massive corals, was investigated. These cells usually see only minimum amounts of light, since most of the light is absorbed in the surface layer of the coral by the coral symbionts. Therefore the oxygen production within the skeleton was measured in relation to various illumination intensities. One result is shown in the 2nd image. Cleary the oxygen production by the ring of endolithic cells can be seen (after an illumination of 37.23µEm-2s-1). The coral was sampled in the lagoon of Heron Island (Capricorn Islands, Great Barrier Reef, Australia) and the experiments were made at Heron Island Research Station.

Larger view on the set-up with the coral in the glass container placed on top of the LED frame while the measuring camera was looking at the cut coral surface from below (pointed upward, sensicam sensimod).

Sample place for the coral, the lagoon of Heron Island, Capricorn Islands, Great Barrier Reef, Australia. Measurements were performed at Heron Island Research Station (HIRS) belonging to the university of Queensland, Brisbane, Australia.

SOURCE: The Cooke Corporation

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