Effects of photoacclimation on the light niche of corals: a process-based approach |
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Authors: | Mia O Hoogenboom Sean R Connolly Kenneth R N Anthony |
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Institution: | (1) ARC Centre of Excellence for Coral Reef Studies and School of Marine and Tropical Biology, James Cook University, Townsville, QLD, 4811, Australia;(2) ARC Centre of Excellence for Coral Reef Studies and Centre of Marine Studies, University of Queensland, Brisbane, QLD, 4067, Australia;(3) Present address: Division of Ecology and Evolutionary Biology, University of Glasgow, Glasgow, G12 8QQ, Scotland, UK |
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Abstract: | The ecology of photosynthetic organisms is influenced by the need to adjust the photosynthetic apparatus to variable light
environments (photoacclimation). In this study, we quantified different components of the photoacclimation process for a reef-building
coral (Turbinaria mesenterina, Lamarck, 1816): including, variation in absorption cross-section, size of photosynthetic units, turnover time, chlorophyll
content, and colony respiration. We used these calibrations to characterize this species’ light niche, and to determine the
sensitivity of the niche boundaries to different processes of photoacclimation. Results showed that the breadth of the light
niche was most sensitive to the size of the photosynthetic unit, absorption cross-section, and rates of respiration. Habitats
with the highest light availability did not lead to maximal energy acquisition. This was because, although corals acclimated
to high light have high rates of photosynthesis per unit chlorophyll, their chlorophyll content was strongly reduced. This
suggests that potential energetic benefits that could be achieved through increased light harvesting (i.e., increased chlorophyll
content) in high-light habitats are outweighed by costs associated with photoprotection. Such costs appear to place an upper
bound on the habitat distributions of coral species. Our approach reveals how the photophysiological processes involved in
photoacclimation interact to determine the light niche. |
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