Project Summary for 2006-13: Evaluating the impact of zooxanthellae physiology and diversity on the loss and recovery of coral-algal symbioses: developing a predictive physiological model for coral bleaching.
The success of modern coral reefs is due in large part to the tightly coupled symbiotic relationship between reef-building corals and endosymbiotic dinoflagellates in the genus Symbiodinium, often referred to as zooxanthellae. Episodes of mass coral bleaching and mortality are among some of the most severe ecological pertubations in coral communities, wherein large numbers of zooxanthellae are expelled from corals in response to when sea surface tempereatures become elevated above summer maximum values, or persist long into the fall season. The global impacts of bleaching have garnered wide scale attention in the scientific community and general public, and some have predicted that such events will increase in frequency due to continued global warming. Current research has pointed to the photosynthetic symbiont as a primary target of cellular damage during bleaching. However, the genetic diversity of these symbionts, coupled with the ability of some corals to harbor multiple symbiont types, has led to the idea that such plasticity could provide and axis for acclimatization or adaptation to climate change if corals can retain and/or acquire thermally tolerant algae, yet our knowledge of the ecological distribution and physiological detail of zooxanthellae is largely incomplete. Current methodologies, such as chlorophyll fluorometry, have proven useful in monitoring coral photosynthetic activity, but several fundamental questions regarding interpretation of data gathered by these methods in light of a detailed understanding of algal photobiology still remain today.
The main objectives of this proposal are 1) further elucidate the cascade and pathways of physiological stress in zooxanthellae at the biophysical and cellular level by using several methods to investigate genetically unique zooxanthellae within experimentally bleached corals, 2) follow the recovery of selected coral species after experimental bleaching in order to discern if different algal populations may influence the stability and resilience of coral-algal symbioses and 3) clarify how results gleaned from experimental bleaching may be compared to rapid in situ point measurement of chlorophyll fluorescence in order to design a more robust predictive model of how such methods may be incorporated into remote monitoring stations to help predict the outcome of future bleaching events. Corals will be sampled from two different depths to account for different patters of photoacclimation as well as symbiont complement both of which may directly influence the photosynthetic thermal response. Algal distribution surveys will be undertaken at multiple spatial and temporal scales and utilize newly developed methods of fluorescence in situ hybridization in order to characterize the full genetic complement of zooxanthellae within marked coral colonies. The outcome of this proposal will have significant broader impacts, as it should provide much needed knowledge toward the question of how (or if) particular species of Caribbean corals can survive future environmental threats such as coral bleaching through symbiont change and/or acclimatization. Likewise this work will develop a better foundation for some potential biochemical differences among zooxanthellae and how they may influence optical signatures of photosynthetic capacity.
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