In April to May 2023, we conducted gamete age assays using eggs and sperm from Porites lobata corals. Porites lobata colonies (minimum diameter 15 centimeters (cm)) were collected from study sites in the Rock Islands Southern Lagoon (Chelbacheb) in the Republic of Palau. Colonies were isolated in individual plastic containers in flow-through seawater tanks at the Palau International Coral Reef Center. Sperm were collected directly from colonies using a large plastic pipette during release. Eggs were allowed to float to the surface so they could more easily be collected by pipette or by skimming the surface with a plastic tri-pour beaker or petri dish. Sperm from selected male colonies were pooled in a single container, and eggs (from n=1 female per batch cross) were gently poured into this pool, allowing fertilization to commence. A small aliquot (~10 milliliters (mL)) of concentrated sperm and ~1000 eggs were added to triplicate wells of a 6-well plate for each time-point. Cell strainers (70 micrometers (μm) mesh) were used to separate eggs from sperm ~45 minutes after fertilization began, and eggs were gently rinsed into a 50 mL beaker filled with 5 μm filtered seawater. Fertilization success was evaluated visually 2-3 hours after fertilization began by observing a sub-sample of the eggs from each cross under a dissecting microscope (Leica S9i) and counting whole (undivided) eggs and dividing embryos.