Limited fine-scale larval dispersal of the threatened brooding corals Heliopora spp. as evidenced by population genetics and numerical simulation

Abstract

Coral reefs are declining worldwide due to regional and global anthropogenic stress. Sekisei Lagoon and areas in its vicinity are impacted by the same stresses. Sekisei Lagoon is the largest coral reef area in Japan covering an area of almost 15 km × 20 km. Being situated upstream of Kuroshio Current, coral reefs in this area could supply larvae to downstream such as the Ryukyu Archipelago, facilitating high biodiversity. To conserve corals in such an area, estimation of larval dispersal among populations is essential because connectivity via larval dispersal is associated with the time for replenishment after disturbance. Isolated coral populations have a higher risk of local extinction. The purpose of this study is to reveal genetically isolated populations of brooding corals with short larval durations in and around Sekisei Lagoon. For this purpose, we utilized both population genetic analysis and larval dispersal simulations. Based on genotyping of 929 colonies of blue coral, Heliopora spp., collected from 22 sites around Sekisei Lagoon, genetic analysis suggested self-recruitment with connectivity in the southeastern sites and northwestern sites. Particle-tracking larval dispersal simulations also revealed similar patterns, corroborating the genetic results. These results suggest that lagoonal scale connectivity among populations of Heliopora spp. in Sekisei Lagoon is limited, as expected based on its short larval duration. Our results highlight the fact that most of the Heliopora spp. populations are genetically isolated, even inside Sekisei Lagoon, implying that the likelihood of being replenished by larval supply from surrounding populations after a disturbance is low and have a higher risk of local extinction than other coral species with high larval dispersal potential.