Reproductive patterns of massive Porites from the Ningaloo World Heritage Reef, Western Australia

Abstract Scleractinian coral populations are declining globally under ocean warming, with repeated mass mortality events increasingly compromising the persistence of coral reefs. Successful reproduction, larval supply and recruitment are critical processes for recovery, yet many aspects of reproductive biology remain poorly resolved for most reef-building taxa, including massive Porites . This study compared reproductive patterns among species in the Porites lobata complex ( Porites lobata Dana, 1846, Porites lutea Milne Edwards & Haime, 1851 and Porites australiensis Vaughan, 1918) using detailed macro- and micro-morphological analyses to identify key diagnostic traits. Our results provide the first insights into the reproductive phenology of massive Porites species at Ningaloo World Heritage Reef. Mature gametes were observed in P . lobata and P . lutea colonies in early autumn (March 2024), coinciding with the region’s peak mass coral spawning event. In contrast, P . australiensis colonies showed no signs of gravidity in either late winter (August 2023) or early autumn (March 2024). Differential spawning times may serve to reinforce reproductive isolation and promote the species divergence of P . australiensis at this location, and this needs to be tested within a phylogeographic framework. Early autumn spawning of P . lobata and P . lutea at Ningaloo differs from the early summer spawning reported for conspecies within the P . lobata complex at Dampier, Western Australia. Regional differences in spawning phenology have potential implications for reproductive isolation, larval connectivity, and local adaptation. Overall, these findings provide preliminary data on the timing of spawning and species boundaries of key Porites species at Ningaloo Reef and highlight the need for broader temporal, spatial, and in-situ spawning observations.