High levels of inorganic nutrients affect fertilization kinetics, early development and settlement of the scleractinian coral Platygyra acuta

Abstract

Dose–response experiments were conducted to investigate the effects of ammonia nitrogen (NH3/NH4+) and orthophosphate (PO43−) on four stages of larval development in Platygyra acuta, including fertilization, embryonic development and the survival, motility, and settlement of planula larvae. Fertilization success was reduced significantly under 200 μM NH3/NH4+ or PO43−. These high doses of NH3/NH4+ and PO4− affected egg viability (or sperm viability and polyspermic block simultaneously) and polyspermic block, respectively. These results provide the first evidence to indicate the mechanisms of how inorganic nutrients might affect coral fertilization processes. For embryonic development, NH3/NH4+ at 25–200 μM caused delay in cell division after 2-h exposure and NH3/NH4+ at 100–200 μM resulted in larval death after 72 h. However, no significant differences were observed in the mobility and survivorship of either planula or competent larvae under different levels of NH3/NH4+ or PO43−. There was a significant (~30 %) drop in the settlement of competent larvae under the combined effect of 100 μM NH3/NH4+ and PO43−. The effects of elevated nutrients appeared to become more significant only on gametes or larvae undergoing active cellular activities at fertilization, early development, and settlement.