Recruitment hotspots: consistent spatial patterns in the relative abundance of coral recruits at One Tree Island, Australia

On coral reefs, sites that receive consistently high levels of recruitment relevant to other sites ("recruitment hotspots") may be crucial to the persistence of populations. However, few studies of coral recruitment have the necessary replication in space and time required to detect recruitment hotspots. The aim of this study was to detect recruitment hotspots at One Tree Reef (southern Great Barrier Reef) and to explore associations between hotspots, hydrodynamics, adult abundance and reef benthos. Recruitment hotspots were detected on the reef slope and in the lagoon. Almost all hotspots were located on the leeward side of the reef, however, there was little congruence among hotspots for different families of coral recruits. Recruitment hotspots in some taxa in some habitats were correlated with water flow or adult abundance. A clear recruitment hotspot for two families (Pocilloporide and Poritidae) in the lagoon had medium levels of water flow (~ 4 cm s⁻¹), but there was no relationship with water flow on the slope. In experimental aquaria, Acropora nasuta settlement was six to 10 times greater under low (2.1 cm s⁻¹) compared to medium water flow (4.6 cm s⁻¹). Abundance of pocilloporid and poritid, but not acroporid, recruits at each site was often correlated with adult cover indicating either aggregative settlement or limited dispersal. Recruitment hotspots are likely to be both sources and sinks for some taxa, and therefore identifying and protecting hotspots should be a high priority in marine reserve design