Spatial variability in recruitment of acroporid corals and predatory starfish along the Onna coast, Okinawa, Japan

Abstract

We compared spatial variability in recruitment patterns between acroporid corals and the predatory crown-of-thorns starfish Acanthaster planci along the Onna village coast of Okinawa Island, Japan. Our objective was to understand population dynamics of both predator and prey. To quantify recruitment, we established artificial recruitment plates for acroporid corals and conducted quadrat surveys for juvenile A. planci at 7 sites. We also examined distributional patterns of adult populations of both species and observed surface currents during larval dispersal periods using GPS-equipped surface drifters. Acroporid recruits typically arrived in greater numbers at more northern sites. Despite high variability, A. planci recruits displayed similar spatial patterns. Drifter trajectories suggest that these spatial recruitment patterns are probably driven by near-shore currents in the summer. Moreover, current data imply a complicated metapopulation relationship in this region, especially for A. planci, new recruits of which may mainly originate outside of the Onna area. Meta - population dynamics within the study area and among surrounding regions must be explained by the complex surface current circulation, because simpler explanations involving only the Kuroshio Current do not adequately describe the relationship between these populations.