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The Blues of coral Reefs

Final Activity Report Summary - BCR (The Blues of Coral Reefs)

During the three years of the Marie Curie International Outgoing Fellowship (IOF) we managed to accomplish the following objectives:

1. We have managed to describe the presences of cryptochromes (blue-light photoreceptors) genes in corals, the simplest multicellular animal phyla (Cnidaria) for the first time. In addition to revealing the evolution and the most primitive characters of these proteins in eyeless animals, we also show that they respond to moonlight and may cue for the largest spawning event on the planet (mass-spawning of the Great Barrier Reef). The results from this work are novel for several reasons. Firstly, it links the enormous understanding of the molecular mechanisms of model animal systems (particularly Drosophila, Danio and Mus) with one of the most dramatic ecological mysteries in nature, that of the highly synchronised mass spawning of reef-building corals and other marine invertebrates. This is one of the most spectacular events in nature, where thousands of species of invertebrates coordinate their spawning over a few nights of the year. Moonlight has been discovered to be a critical cue for coordinating mass spawning yet we have had no real idea on what molecular mechanism might be involved. We show that expression of Acropora millepora cryptochromes are light dependent and also synchronised with the phases of the moon (cry2) and therefore may serve as good candidates for being involved in the molecular mechanisms underpinning the coordination of light responding behaviours and mass spawning in tropical oceans.

The second reason that we believe our work has major significance is that it provides a critical piece of the puzzle to the evolution of cryptochromes in the animal kingdom. Our work shows the structure of several important cryptochromes types from the simplest multicellular animal (eumetazoan), with substantial implications for our understanding of how cryptochromes have evolved. At present, Cryptochromes are known from advanced animals such as Drosophila and Homo. Understanding the roots of the evolution of eumetazoan animal cryptochromes will be critical to understanding how eumetazoan animal cryptochromes are related to those found Arabidopsis, algae and other plants.

The results from this study were published in Science 2007, vol. 318, pp. 467-470.

2. During the spawning season of November 2006 we managed to show the link between light and light spectra to the spawning behaviour. The abstract of the results is shown below. Light and light spectra affect the mass spawning timing in the GBR The synchronised mass spawning event in the Great Barrier Reef Australia is an annual cycle in which corals release their gametes into the water column once a year following the full moon. This phenomenon is controlled by temperature, tides, rain and light. It is suggested that light can effect and desynchronise the timing of the gamete release. Here, we show that two species of corals Acropora millepora and Acropora aspera were phase shift in their spawning time when the day length was artificially extended by a period of six hours. Corals colonies which were illuminated by red light spectra did not show any delay in the spawning time, and showed similar spawning time which was recorded at their natural habitat at the reef.

However, colonies irradiated by blue, green and white (PAR) light spectra had a phase shift in their spawning time when compared to the reef and the control colonies spawning time. These findings suggest that artificial light 'contamination' in the blue and green spectra regions can mismatch and delay spawning times in those colonies tested, while red light has no effect on the spawning behaviour. The results may imply on the presence of blue light photoreceptors known as cryptochromes which mediate this circadian spawning behaviour.