Optimising conditions for in vitro fertilization success of Acropora tenuis, A. millepora and Favites colemani corals in northwestern Philippines

Abstract Fertilization is a critical life history event and important to population dynamics. Successful fertilization relies on encounters of compatible and viable sperm and eggs. Scleractinian corals that spawn their gametes directly into the water column may experience limitations from sperm dilution and delays in initial sperm-egg encounters that can impact successful fertilization. Notably, the same issues can be experienced when conducting ex situ larval culture. Therefore, experiments were completed using spawned eggs and sperm of the reef corals Acropora tenuis, A. millepora and Favites colemani to determine the optimal ranges of sperm concentrations ( 65%) and > 90% fertilization rates for F. colemani. Sperm concentrations of 105–107 mL−1 resulted in the highest observed fertilization rates for all three species (>90%). High fertilization rates (>80%) occurred when eggs and sperm were combined after 30 min and up to 2 h after spawning for F. colemani and up to 4 h for A. tenuis and A. millepora gametes. Fertilization rates were significantly reduced (