Determining Protective Nutrient Thresholds for the Early Life Stages of Corals

Multiple concentration-response experiments were conducted to determine the impact of the phosphate, nitrate, ammonium and urea on the fertilization and larval survival/settlement of six critical coral species (Colpophyllia natans, Diploria labyrinthiformis, Montastraea cavernosa, Orbicella faveolata, Orbicella franksi and Pseudodiploria strigosa). The results of these experiments revealed that two species were susceptible to elevated nutrients. First, cell division during fertilization of Diploria labyrinthiformis was found to be impacted by increased levels of phosphate. The Half Maximal Effective Concentration (EC50), or the phosphate concentration at which the number Diploria labyrinthiformis eggs achieving a 4-cell state (i.e. undergoing 2 cell divisions) had fallen to 50% of the initial numbers was determined to be 0.33 μmol L-1. Second, larval survivorship during settlement for Montastraea cavernosa was found to be impacted by increased levels of nitrate. The EC50, or the nitrate concentration at which the number of surviving Montastraea cavernosa larvae (either swimming or settled) had fallen to 50% of the initial numbers was determined to be 11.5 μmol L-1. The EC50 values determined by this study provide a benchmark for the mitigation of phosphate and nitrate levels along Florida’s Coral Reef Tract.