Practical applications of variability in thermal tolerance of reef-building coral in a changing climate [electronic resource]

Natural ecosystems are faced with threats of climate change and rising temperatures and are expected to exceed biological thresholds in many systems in the foreseeable future. However, ecosystems consist of individual organisms that vary in their inherent natural tolerance to changes in climate, in particular to thermal resilience. A better understanding of this variation in resilience is critical to ensure that the services from natural ecosystems persist into future. In this thesis, I focus on thermal tolerance in coral reef ecosystems to explore variability across space (at individual and species levels at small and large geographic scales) and time (through seasonal acclimatization) to better understand how to build resilience in coral reef ecosystems. First, I demonstrate the important role of individual variation of coral colony hosts in reef restoration processes and assess the maintenance of thermal tolerance through two consecutive natural bleaching events in American Samoa. From this work, I characterize simple proxies of thermal tolerance that allowed the identification of resilient individuals before bleaching occurred. I then take a closer look at the gene expression response to acute bleaching stress after two distinct periods of natural seasonal acclimatization in two coral species in American Samoa. I show that a surprisingly small portion of the transcriptome reacts significantly to heat stress in both seasons. After characterizing orthologous regions across the two tested species, I also show that their response to heat stress is similar to each other only after a period of acclimatization to more variable temperatures. I then expand our understanding of the shared transcriptomic response to heat stress to five species of reef-building coral. Using orthologous regions across species, I characterize sets of orthologs that respond across species that bleach, sets of orthologs that respond across species of the same genera, and sets of orthologs that respond in a species-specific fashion. I then test biomarkers characterized in other studies of coral response to heat stress and map them to orthologous regions across species. Using these orthologous regions, I validate sets of biomarkers that detect thermal stress across all five species of coral. Finally, in the coral reefs of Palau, I search for more populations of resilient coral across a broader geographic scale. I show that patch reef environments in Palau have both high and low variability thermal environments similar to those characterized in American Samoa. However, after testing the thermal tolerance of coral from these distinct thermal environments, I show that they do not differ as expected but rather exhibit exceptionally high overall thermal tolerance. Taken together, the dissertation demonstrates the critical role of individual variation in thermal tolerance in understanding and ultimately managing coral response to climate change.

Keywords: Biology.
Advisor: Palumbi Stephen R.
Crowder Larry B.
Hadly Elizabeth Anne
Sherlock Gavin advisor. Thesis advisor