Scleractinian (reef-building) corals are among the most efficient biomineralizing organisms in nature. They have formed vast coral reefs in the shallow waters of the tropics and sub-tropical oceans since the Permian mass-extinction. Thus, the importance of scleractinian corals to global ocean chemistry, nutrient cycles, and the continental shelf-environment in particular, cannot be underestimated. Reef-building corals are generally restricted to depths of up to 100 m due to their symbiotic relations with the photosynthetic dinoflagellate algae (called zooxanthellae), which provide much of the energy needed by the coral holobiont by means of photosynthesis. Many animals and plants have formed symbioses over evolutionary time. These symbioses are typified by tightly coupled mutualistic interactions, and the unique circumstance of one type of organism living within the other (endosymbiosis). The net result is a highly co-evolved and efficient system that has the potential to thrive in places where comparatively less coupled associations do not. Paradoxically, although there are some indications for rhythmic behavior, very little is known about the circadian clocks that control the biology of these symbiotic organisms. There is no clear evidence from molecular or physiological perspectives for circadian mechanism controlling the metabolism, photosynthesis, or calcification process involved in the formation of these calcium carbonate skeletons (polymorph aragonite). The scientific objectives of our research are to reveal the fundamental molecular and physiological circadian clock apparatus in symbiotic corals and their interaction with light and temperature variations, two key clock synchronization signals. The aims are:
I. To investigate the circadian clock mechanism of the coral host in relation to the environmental cues of light and temperature.
II. To explore the endosymbiotic symbiodinium circadian machinery in relation to light and temperature cues.
III. To study whether skeleton calcification, skeletongenesis, is regulated by the coral circadian rhythm.
Our research will center on the circadian clock of one symbiotic coral, and its associated zooxanthellae (the system). This system will be investigated in terms of three of its components, the coral (animal), the symbiotic algae, and the skeleton. Studying symbiotic scleractinian corals as a model organism can serve as an excellent system for understanding the molecular, genetic, and developmental complexity of the metazoan circadian clock; corals are likely to be critically important from an evolutionary point as this phylum is regarded as the sister group to the Bilateria, and known to be the simplest eumetazoan marine organism.
To achieve this objective, a combination of techniques from different areas will be integrated to study the coral circadian clock biology process, molecular and cellular biology, physiology, high-precision stable isotope mass-spectrometry, and quantitative nano-scale ion-microprobe technology, and will leverage our vast experience with coral growth and maintenance in both natural and controlled laboratory environments. This is a unique and novel mix of scientific methods applied to a problem of fundamental importance to coral reef chronobiology, ecology, and physiology.