Abstract
Coral reefs are one of the most biodiverse and important marine ecosystems on Earth; however, they are currently in extreme decline around the world due to warming sea temperatures caused by anthropogenic climate change. A healthy coral consists of a cnidarian host living in harmony with endosymbiotic dinoflagellate algae (Symbiodiniaceae) as well as a large diversity of endosymbiotic bacteria, viruses, and micro-eukaryotes, which are altogether termed the “coral holobiont”. Most research to date has focused on the coral- algae symbiosis; however, there is mounting evidence that coral-associated bacteria have key functional roles within the coral holobiont that affect holobiont physiology, environmental resilience, and evolution.The genome of Pocillopora damicornis, a cosmopolitan Indo-Pacific coral species, found enrichment for genes involved in innate immunity, including microbial recognition, signaling pathways, and cellular defense mechanisms. It is hypothesized that this immune gene family expansion and diversification is linked to the maintenance of specific beneficial coral-bacteria symbioses. This Ph.D. dissertation investigates the complex interactions between Pocilliopora spp. corals’ innate immune systems and endosymbiotic Symbiodiniaceae and bacteria communities using controlled aquarium experiments and high-throughput sequencing analyses. Collectively, this research 1) characterizes the extent and diversity of the Pocillopora innate immunity gene repertoire 2) determines how bacterial lipopolysaccharide (LPS) exposure stimulates P. damicornis and P. acuta innate immunity gene expression and affects the endosymbiotic bacteria community composition, 3) characterizes the effects of antibiotics treatments on P. verrucosa and P. meandrina bacteria community composition and coral host physiology, and 4) investigates how Pocillopora spp. coral holobionts respond differently to heat stress with and without prior antibiotic treatments that disrupt the coral-associated bacteria community.