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Corals Play Role in Bleaching, Study Says

Scientists use cancer detection device to determine how coral reefs scatter light.

April 30, 2013

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Certain corals play a role in their susceptibility to bleaching by scattering light differently than others, according to a paper published in the journal PLoS One.

Northwestern University molecular biologist Luisa A. Marcelino, Vadim Backman, a physicist and professor of biomedical engineering at Northwestern, and Mark W. Westneat, a coral reef biologist and curator of zoology at the Field Museum in Chicago used optical technology designed to detect cancer and discovered that some reef-building corals and more importantly, their skeletons, scatter light in different patterns to the algae that feed the corals.

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Coral reef

           

Figure 1. Light transport in coral skeletons.

A – Visual demonstration of differences in light transport shown for three taxa as described in [10] by focusing a laser on (a) highly-absorbing black surface and on skeletons of (b) Leptastrea transversa, (c) Leptoria phrygia, and (d) Seriatopora caliendrum. Microscopic light-scattering properties of skeletons were measured using LEBS with a white light source. B – Schematic representation of the redistribution of light between sun-exposed versus shaded areas. Differences in light transport are shown for corals with (a) very high skeleton and a (b) low skeleton. Skeletons capable of longer light transport (i.e. longer or low ) are able to illuminate otherwise shaded areas in the colony and this increased redistribution between sun-exposed versus shaded areas of a colony may further amplify the light available to the algae: (I) downwelling light, (II) diffuse reflectance, (III) photon path (arrows) and sub-micron scatters (black dots), (IV) diffuse reflectance illuminating a shaded algal cell in the coral tissue: the skeleton serves as a secondary light source [9].

 Source: PLoS One Journal

This research led to the determination that corals more efficient in scattering light suffer more damage when stressed than those corals that are not as efficient at scattering light. They also found that these less efficient light scatterers have the capability to retain algae better under stressful conditions and are more likely to survive a bleaching incident.


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The research is interesting due to the method that was employed to reach their conclusions as it involved marine biology, the physics of light transport, biophysics of how corals respond to light, and the optical technology used for early cancer detection. They used a technique called low-coherence enhanced backscattering (LEBS) to measure light transport and amplification on the skeletons of 96 different coral species. According to the paper, they found that the speed in which light amplification increases with the loss of algae is dependent on light transport at the microscale. This was determined using the LEBS technique. Those corals that lost more algae were more prone to bleaching. The specimens that were used in the study came from the Field Museum collection, of which many of the corals were displayed at the Chicago Columbian Exposition and World's Fair of 1893. The determined that bleaching and light scattering occurs across the history of coral reefs and occurs in all major coral groups.

 

The complete paper can be found here.

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