Recruitment of juvenile corals onto coral tables preyed upon by Acanthaster plana

Abstract

Corals of 3 table-forming species of the genus Acropora, whose tissues had been removed by the seastar Acanthasterplanci (L.) during 2 mo prior to a major annual coral-spawning season, acted as substrata onto which juvenile corals settled. Juvenile corals were detected microscopically in the laboratory on samples taken from tables 10 wk after spawning time (mean diameter of juveniles 1.3 mm; density 3.5 per 100 cm2). Previously it had been thought that a delay of at least 1 yr was necessary before corals would settle after predation by A. planci. The same tables were sampled again after the next coral-spawning season (1 yr later). Desplte the presence of algae and other colonizing organisms, new corals had settled at a density of 2.8 per 100 cm! About 34 41 of the previous year's juveniles had survived, and mean diameter of these was now 7.24 mm When tables were searched closely in the field, surviving juveniles and some new recruits (with diameters down to 2.00 mm) could be detected. These results indicate that apparent delay in settlement after predation by A. planci can be due to the small size of newly settled corals, which can only be seen by careful inspection of the substratum during the first year after settlement, and which do not achieve 3-dimensional structure until some time later. A. planci was still present at the slte when these observations were made. Thus re-establishment of the coral community on this reef had begun during the time that the adult community was being preyed upon.