Coral tissue traps light for algal partners

Although the interaction between coral tissue and light is central to a basic understanding of coral physiology coral tissue optics has received relatively litle attention. Now new research, using fibre optic and electrochemical microsensors along with chlorophyll fluorescence imaging, has revealed a new mechanism by which light is transferred over a coral colony.  This important study reveals the dynamic nature of coral tissue and paves the way for a more detailed understanding of coral photobiology including coral bleaching mechanisms.

The research team from UTS C3 and the University of Copenhagen demonstrated for the first time that light is trapped and transferred laterally in coral tissue. The results, published in The Journal of Experimental Biology, showed that this captured light improved the  photosynthetic efficiency of the algal symbionts in the coral tissue.

Lead author, C3 PhD student Daniel Wangpraseurt said that knowing that terrestrial plant leaves actively trap and redistribute light to improve photosynthesis led his supervisor Professor Michael Kuhl to consider if corals do the same for their algae.

"It was assumed that the coral skeleton was mostly responsible for scattering light in coral polyps. Our research shows definitively that coral tissue plays a major part in trapping and redistributing light. The coral animal actively helps transfer light horizontally through the coral tissue to help its algal symbionts photosynthesise more efficiently," he said.

Corals were collected from Heron Island on the Great Barrier Reef and transported back to UTS C3 coral tank facilities where Daniel performed intricate measurements, using microsensors, to measure the amount of light transmitted through the animal to different depths and the impact on oxygen production in the algae.

The team concludes that since skeleton and tissue optics vary considerably between corals a more detailed understanding of the optical mechanisms underlying lateral light transfer should be a core component of future photobiology research.

The image above, taken by Daniel, was chosen for the front cover of the February edition of the The Journal of Environmental Biology. This image shows a microelectrode mapping the spatial heterogeneity in Oxygen  concentration and symbiont photosynthesis at the level of individual coral polyps.

Links:

• Daniel Wangpraseurt, Anthony W. D. Larkum, Jim Franklin, Milán Szabó, Peter J. Ralph and Michael Kühl, Lateral light transfer ensures efficient resource distribution in symbiont-bearing corals doi: 10.1242/jeb.091116 February 15, 2014 J Exp Biol 217, 489-498.
• Live Science interview with Daniel gives further insight to this research.