Acute sedimentation causes size-specific mortality and asexual budding in the mushroom coral, Fungia fungites

Abstract

Field experiments investigated the effect of acute sedimentation on polyp injury, mortality and bud production in the mushroom coral, Fungia fungites (Linnaeus, 1758). Small (3-5 cm), medium (8-12 cm) and large (15-20 cm) polyps were covered with a layer of sediment in low (2 mm), medium (5 mm) and high (10 mm) treatments, every two days for 20 days. Injury decreased with polyp size, and increased with the amount and duration of sediment addition. Only medium and large polyps briefly (<6 days) survived the high-sediment treatment, which simulated deposition following severe storms and cyclones. The medium-sediment treatment simulated deposition following storms, and over half (60%) the medium-sized polyps survived a week without injury, whereas one-third of the large polyps survived the experiment without injury. The low-sediment treatment simulated deposition following large tides, and most (80%) medium and large polyps survived this treatment without injury, as did one-third of the small polyps. Injury caused mortality in all polyp sizes. Injuries usually spread to the entire polyp within a week of continued sediment addition and within seven months of background sedimentation. Apart from the small-polyp size class, almost half the polyps that had lost visible tissue during the experiment produced asexual buds. The number of buds on a polyp was positively related to its initial size, and inversely related to the sediment load to which it was exposed.