Genotypes of Acropora cervicornis in Florida show resistance to either elevated nutrients or disease, but not both in combination

Coral restoration programs are expanding to revive coral populations and ecosystem services, but local and global stressors still threaten coral survival. In the Caribbean, the ESA-listed staghorn coral Acropora cervicornis has experienced profound declines due to multiple stressors, including disease and nutrient pollution. We studied the impact of these two stressors on ten A. cervicornis genotypes for which disease susceptibility was previously ranked in a disease transmission experiment. Results showed that elevated ammonium, disease, and their combination negatively affected A. cervicornis survivorship, with variable susceptibility among genotypes. Three genotypes were susceptible to elevated ammonium alone and experienced mortality in up to 80% of their fragments. Exposure to a disease homogenate under ambient ammonium caused mortality in 100% of the fragments in four coral genotypes, intermediate mortality in five (33-66% of their fragments), and no mortality in one genotype. However, all genotypes experienced mortality (30-100% of their fragments) when exposed to both elevated ammonium and disease. Despite the detrimental effects of ammonium on coral survivorship, corals under elevated ammonium presented higher photochemical efficiency (Fv/Fm) of the algal symbionts. Disease susceptibility did not align with the genotypic ranking established in a previous study, suggesting that, while genotypes may vary in their disease resistance, rankings may change due to environmental factors or disease type. Regardless of individual susceptibility, our results suggest that water quality improvement is necessary for increasing A. cervicornis survivorship.