Dissertation

Influence of Environment and Climate Change on Coral-Associated Microbial Communities and Trophic Strategies

Price, James T

2020

Overview

Global increases in atmospheric CO2 are leading to ocean warming and acidification, causing more frequent occurrences of coral bleaching, outbreaks of disease, and as a result, widespread coral mortality. Yet, some corals appear to be more tolerant of the effects of a changing climate than others. This has been attributed to several parameters of coral physiology, including greater levels of energy reserves and the ability to incorporate more heterotrophic resources, or hosting more thermally tolerant lineages of endosymbiotic algae (i.e., Symbiodiniaceae). The bacteria and archaea associated with a coral, hereafter referred to as microbial communities, are also thought to support corals by changing in response to environmental conditions, potentially providing a first line of defense as corals attempt to acclimatize. However, it is unclear whether most corals will be able to adapt or acclimatize to ocean warming and acidification expected by the end of this century. Further, little is known about potential connections between parameters of coral physiology and their associated microbial communities, and how they may affect the ability of a coral to persist in the face of global climate change. To explore this, a two-pronged approach was used: (1) a natural survey of corals around the island of O`ahu, Hawai`i, with corals collected from several sites across a gradient of ocean conditions to assess natural variability in the coral-associated microbial community composition and coral trophic strategies, and (2) a 22-month mesocosm experiment, where corals were exposed to chronic temperature and pH stress to explore potential relationships between coral-associated microbial communities and the ability of corals to persist in end-of-century ocean conditions. The natural survey revealed a diversity of microbial associates and trophic strategies among the Hawaiian corals, with the greatest differences often occurring among species rather than among locations. For the first time, the microbial community diversity was also found to correlate with the relative contribution of heterotrophy among corals, suggesting that resource use by Hawaiian corals and the structure of their microbial communities are intertwined. The 22-month mesocosm experiment revealed connections between coral-associated microbial community composition and coral mortality under predicted end-of-century ocean conditions. Specifically, two patterns were found, where Porites compressa and Porites lobata had lower mortality and their microbial communities changed in response to experimental heat and acidity stress, while Montipora capitata and Pocillopora acuta had greater mortality and their microbial communities appeared generally inflexible.Overall, the findings of this dissertation research suggest that Hawaiian corals host a diverse range of microbial communities and employ a variety of trophic strategies, such that Porites compressa and Porites lobata corals are likely to be more tolerant of stress than others and more likely to persist through this century. The coral trophic strategies were also related to the composition of the microbial communities, supporting past hypotheses of close connections between coral health and the microbiome. This was confirmed in the mesocosm experiment, as Porites compressa and Porites lobata hosted flexible microbial communities and had lower mortality in predicted end-of-century conditions than Montipora capitata and Pocillopora acuta, suggesting that those corals which are more plastic in their response will likely be more tolerant of changing ocean conditions. However, some species and populations of coral remain susceptible to the stresses expected with global climate change by the end of this century and are less likely to persist.

• Publisher: ProQuest Dissertations & Theses
• Subject: Biology / Climate Change / Microbiology
• ISBN: 9798780609292