Abstract
Tropical scleractinian coral reefs are one of the most biodiverse ecosystems on planet Earth. In the Anthropocene, these ancient coral lineages are declining due to a wide variety of stressors, including disease. In the Caribbean, coral disease is a massive crisis in need of immediate remedies. This study aimed to explore the relationships between ammonium over-enrichment, symbiont abundance, and disease susceptibility in the threatened Caribbean Staghorn coral Acropora cervicornis. Contrary to expectations, we found no significant difference in symbiont abundance in ammonium-enriched corals compared to controls, even when comparing within the same coral genotype. This could be due to the naturally high ammonium concentrations in our relatively open flow-through systems, and/or due to the intracellular dynamics of nutrients in corals. Nutrients and disease exposure both significantly influenced coral mortality over the course of the entire experiment, but there was no interaction between the two factors. Similarly, there were strong genotypic effects: of the 10 genotypes included in the experiment, seven were unaffected by nutrients alone, one was unaffected by disease alone, but none were resistant to nutrients and disease together, suggesting that improvements in water quality may be needed in order to maximize survivorship during disease outbreaks.