Functional and genetic diversity of symbiotic dinoflagellates (genus: Symbiodinium) in reef-building corals
Kemp, Dustin William
MetadataShow full item record
The relationship between reef-building corals and symbiotic dinoflagellates (genus Symbiodinium) enable corals to exist in oligotrophic tropical and sub-tropical oceans. Symbiodinium enhance coral calcification rates and provide greater than 90% of coral’s metabolic requirements via photosynthetically fixed carbon. In return, corals provide Symbiodinium with a nutrient-rich place to reside. Symbiodinium are highly diverse and can occur in symbiosis with mollusks, protists, and cnidarians including reef-building corals. This dissertation studies the ecology and physiology of genetically diverse Symbiodinium. A novel technique for sampling coral was developed and used throughout these works enabling hundreds of samples to be taken from a single coral whilst causing minimal damage to the coral. Using this technique, Symbiodinium community structure of the Caribbean coral Montastraea faveolata was documented and indicated geographic specificity and local irradiance driven zonation patterns. To investigate coral-Symbiodinium physiology in “high-light” and “low-light” regions of M. faveolata physiological parameters were measured examining Symbiodinium community structure, photobiology, and calcification rates. Results showed genetically different Symbiodinium displayed differential “high-light” or “low-light” photo-physiological and photoacclimation responses indicating niche specialization within M. faveolata, which ultimately influences coral physiology. Finally, corals response to two separate environmental stresses was studied. Community structure and physiology of Symbiodinium associated with M. faveolata was studied during a coral bleaching event in Puerto Morelos, Mexico. A post-bleaching shift in Symbiodinium communities was documented and thermally tolerant Symbiodinium ITS-2 types A3 and D1a were predominant. These results indicate functional differences between genetically distinct Symbiodinium populations that may facilitate competitive exclusion of thermally sensitive Symbiodinium types resulting in the abundance of tolerant opportunistic Symbiodinium. During the winter of 2010 abnormal cold temperature in the upper Florida Keys resulted in mass mortality of many inshore reef-building corals. Following this event, the physiological effects of low temperature on three common reef-building corals (Montastraea faveolata, Porites astreoides, Siderastrea siderea) were experimentally investigated. This study documented species-specific physiological responses indicating different coral and/or zooxanthellae cold tolerances. Visual surveys of inshore reefs corroborated experimental results, with S. siderea being minimally affected by the cold-water anomaly whereas M. faveolata and P. astreoides experienced approximately 100% mortality.