Predation on coral larvae by corals from the Great Barrier Reef

Gametes from colonies of the coral Acropora tenuis (from Magnetic Island) and from Acropora millepora (from Davies Reef) were collected after spawning in tanks. Colonies of several corals (Acropora digitifera, Acropora formosa, Acropora latistella, Acropora secali, Acropora verweyi, Galaxea astreata, Goniastrea aspera, Goniopora pandoraensis, Platygyra pini) and two zoanthids (Palythoa tuberculosa, Zoanthus sp.1.) species were collected from inshore reefs near Townsville for the feeding experiments. The feeding experiments were conducted in flow chambers at gentle water flow. They commenced when the larvae were 3 days old, and continued until the numbers of free-swimming larvae were depleted by the experiments, and by settlement and/or metamorphosis which occurred at about 11 days (Acropora tenuis) or 13 days (Acropora millepora) after spawning.Experiments were run at night or day, depending on the time of polyp expansion in each of the predating coral species: Goniopora pandoraensis and Galaxea astreata tended to expand during the day and often contracted at night, whereas most faviids and Acropora spp. only expanded at night. Species, growth form (submassive, massive, branching, stolon-connected solitary polyps); percent depletion of larvae by actively feeding corals and zoanthids (D); controls (N0) after 2-h exposure. Significance levels of difference between numbers of surviving larvae among coral genera (with and without zoanthids), and between the two species of larvae were calculated. The study shows that (if the laboratory experiments are indicative of events in thefield) coral larvae are at high predation risk during their final period in the plankton, when they become negatively buoyant and search for a suitable settlementlocation. Larval mortality around reefs due to predation by non-acroporid corals could significantly affect recruitment rates on reefs with high coral cover. However, predation by corals will be insubstantial in areas of low coral cover, where successful coral recruitment will have the greatest bearing for recovery after disturbance.
 The ability of some hard coral and zoanthid species to prey upon coral larvae under experimental conditions in flow chambers was investigated.Because hard corals occupy a large proportion of the reef area, their feeding behavior and food selectivity (be it indiscriminate predation, or avoidance of propagules from phylogenetically related taxa) are likely to contribute to affect recruitment rates on reefs.
 Because scleractinian corals occupy a large proportion of the area on many coral reefs, their feeding behavior and food selectivity (be it indiscriminate predation, or avoidance of propagules from phylogenetically related taxa) are likely to contribute to affect recruitment rates on reefs.Only runs in which the corals remained expanded throughout the experiment were included in the analyses, resulting in uneven numbers of replicates per species. Several species of Acropora were tested but data from all Acropora species were later combined due to the low number of successful runs and consistently weak responses in all species.

Organization: Australian Ocean Data Network