Award: OCE-1923926

Our collaborative project between Oregon State University and Mote Marine Laboratory studied the interactions among the coral animal, its resident bacteria, and the environment to understand how these factors work together to ultimately affect coral health. Our preliminary data showed that the high abundance of an obligate parasite of Caribbean staghorn corals (Acropora cervicornis), called Aquarickettsia rohweri, is not only associated with reduced growth rates, but also a high susceptibility to disease in some corals. Using nutrient exposure experiments designed to alter the interactions of the bacterium Aquarickettsia within disease-susceptible genotypes (i.e., individuals with distinct genetic makeup) of Caribbean staghorn corals, this project tested several hypotheses regarding marine host-microbe-environmental interactions and disease susceptibility. Initially, to better understand the microbe of interest we studied the life history of the bacterial-coral interaction and showed that Aquarickettsia is likely transmitted horizontally from one individual coral host to another, perhaps from other adult staghorn corals located within the same reef sites, and not directly from parent to offspring. Meanwhile, Aquarickettsia appears to be evolving independently of its coral host, indicating that it can rapidly adapt to new climates and hosts a cosmopolitan parasite. Additionally, microbial signatures of staghorn genotypes from different regions within the Florida Keys were retained even after translocation to novel regions for years, suggesting that the coral host may be mediating its own microbiome. Finally, coral genotypes with a high abundance of Aquarickettsia were indeed more susceptible to white band disease compared with genotypes that had a more diverse microbiome with low abundance of Aquarickettsia. Our nutrient enrichment studies showed that phosphates in particular caused an increase in the abundance of Aquarickettsia within disease-resistant staghorn corals and a subsequent reduction in coral growth rates, while corals exposed to nitrates showed no difference from control treatments. Furthermore, while three weeks of nutrient enrichment did not alter disease-resistant genotype microbiomes, six weeks of nutrient enrichment reduced growth rates and disrupted the coral microbiome, suggesting that even robust genotypes may succumb to alterations after more sustained environmental pressures. Analysis of Aquarickettsia gene expression in host corals exposed to nutrient enrichment showed increased activity in Aquarickettsia nutrient importation genes and genes involved in infectivity, suggesting that nutrient enrichment may exacerbate infection by the parasite Aquarickettsia. Our final set of experiments confirmed data from previous studies showing that genotypes of A. cervicornis dominated by the coral parasite Aquarickettsia were more susceptible to disease than genotypes with diverse microbiomes and low Aquarickettsia. However, when comparing nutrient enrichments with previous exposure to high water temperatures, we found that the strongest predictor of disease development for each genotype tested was prior exposure to increased thermal stress rather than nutrient enrichment. Here, disease-resistant genotypes remained more robust with less disease-associated mortality compared with disease-susceptible genotypes, but those that were heat-stressed were no longer completely disease resistant. Initial analysis suggests that production of immune proteins in corals with diverse microbiomes and low Aquarickettsia was higher than immune protein activity in corals with high abundances of Aquarickettsia. Ultimately, these series of studies have highlighted the importance of the host-microbiome-environment interaction on coral physiology and health. Further understanding and potentially manipulating this tripartite to encourage more robust coral health will be essential to recover critically endangered species such as the Caribbean staghorn coral. In addition to the targeted research outlined above, Mote education staff coordinated several presentation opportunities from women in science that study microbial and molecular aspects of corals. Female scientists delivered lectures to high school students, discussed their passion for microbes, and provided insight into juggling life demands as well as career expectations. In addition, education staff designed a residential program titled Investigate Environmental Health. School groups of various ages (middle school to college) were invited to stay overnight at Motes Elizabeth Moore International Center for Coral Reef Research and Restoration laboratory in Summerland Key, FL. Mote hosted 442 students who participated in a multi-day hands-on investigative research project culturing bacteria and assessing reef health in restoration outplant locations. Activities included water quality monitoring, water sample collection, culture-based bacterial assays, underwater survey methodology, visual health assessments of both our ex-situ nursery system and in the field at Looe Key Reef, and hands-on lab experiments investigating the spread of coral disease and mitigation techniques. Additionally, Mote education staff developed several classroom-based lessons and corresponding activities to help students develop skills related to coral reefs and microbiology. A total of 1,587 participants engaged in 89 total programs focused on coral and microbial research associated with this NSF award. Last Modified: 11/29/2023 Submitted by: ErinnMMuller