Experimental evaluation of nutrient and disease treatment effects on Acropora cervicornis (NCEI Accession 0299892)

Acropora cervicornis fragments of each genotype were evenly and haphazardly assigned to two nutrient treatments: ambient nutrients (Ambient) or elevated ammonium (NH4). Each nutrient treatment was replicated in four independent tanks (n = 3 fragments per genotype per tank). For ~1.5 months (47 d), Ambient tanks were maintained under nutrient levels consistent with the values in Virginia Key, FL, while elevated NH4 tanks were dosed with NH4Cl [3 mM] every 15 minutes using peristaltic pumps. The initial NH4 dose volume was 10 mL of the stock solution, targeting a ~10 μM increase in NH4 concentration. These values were calculated to account for the dilution of the nutrients resulting from adding new ambient seawater to the tanks (200 mL/min in a total tank volume of 180 L). After detecting higher than normal NH4 concentrations in the incoming seawater from Biscayne Bay, the NH4 dose volume was lowered to 5 mL of the stock solution, targeting ~5 μM NH4 increase above ambient values. The fragments were also assigned to disease vs. placebo treatments, the disease treatments involving exposure to homogenates of corals showing signs of white band disease following the protocol found in Rosales & Palacio-Castro (2024).

Water samples (~40 mL) were collected to monitor NH4 levels in the treatments and immediately refrigerated at 4C. The elevated NH4 tanks were sampled daily, but the Ambient tanks were sampled less frequently (~2-3 days and no samples were collected during weeks 1 and 3 of the experiment). Nutrient concentrations were measured at NOAA-AOML using an AA3 nutrient analyzer (Seal Analytical, Southampton, UK). The instrument was calibrated before each run using standard solutions and procedures. Initially, only NH4 was monitored, but after high NH4 concentrations in the source seawater were detected, additional measurements of PO4 were included.