Ex situ spawning, larval development, and settlement in the massive reef-building coral Porites lobata in Palau

Reproduction, embryological development, and settlement of corals are critical for survival of coral reefs through larval propagation. Yet, for many species of corals, a basic understanding of the early life-history stages is lacking. In this study, we report our observations for ex situ reproduction in the massive reef-building coral Porites lobata across two years. Spawning occurred in April and May, on the first day after the full moon with at least two hours of darkness between sunset and moonrise, on a rising tide. Only a small proportion of corals observed had mature gametes or spawned (17 - 35%). Eggs were 185 - 311 m in diameter, spherical, homogenous, and provisioned with 95 - 155 Symbiodiniaceae algae. Males spawned before females, and ex situ fertilization rates were high for the first 2 hours after egg release. P. lobata larvae were elliptical, approximately 300 m long, and symbiotic. Just two days after fertilization, many larvae swam near the bottom of culture dishes and were competent to settle. Settlers began calcification two days after metamorphosis, and tentacles were developed 10 days after attachment. Our observations contrast with previous studies by suggesting an abbreviated pelagic larval period in P. lobata, which could lead to the isolation of some populations. The high thermal tolerance and a broad geographic range of P. lobata suggest this species could locally adapt to a wide range of environmental conditions, especially if larvae are locally retained. The results of this study can inform future work on reproduction, larval biology, dispersal, and recruitment of P. lobata, which could have an ecological advantage over less resilient coral species under future climate change.