Damage and recovery of four Philippine corals from short-term sediment burial

Abstract

Recovery of corals after full burial with littoral sediment (16% silt, 46% fine sand and 38% coarse sand; 28% CaCO3) was monitored in 2 field experiments at the reefs off Lucero, Bolinao (Pangasinan, NW Philippines), from April to May 1996. In the first experiment at 2 m depth, Porites was buried for 0, 6, 20 and 68 h; a second experiment was done at 5 m depth and 4 common taxa (Porites, Galaxea, Heliopora and Acropora) were buried for 20 h. At 2 m depth, Porites was not affected by 6 h burial compared to the controls that were not buried. Increasing burial time had increasingly more serious effects. Burial for 20 h resulted in increased discoloration of the coral tissue. After 68 h of burial, up to 90% of the tissue bleached in the first days. About 50% of this tissue disappeared subsequently and bare coral skeleton became exposed or were covered with algae. After a few weeks, however, recovery took place: the bare areas were recolonized from surrounding surviving tissue or from highly retracted polyps in the affected area. In the corals that had been buried for 20 h no more significant differences from the controls were observed after 3 wk. For those that were buried for 68h, this was the case after 4 wk. At 5 m depth, all Acropora died after the 20 h burial treatment, but the other taxa recovered in a comparable way to the Porites in the first experiment at 2 m depth. It is concluded that complete burial will cause considerable whole-colony mortality in at least Acropora, and thus may result in a permanent loss of coral taxa from reefs that are subject to such intense sedimentation events. Less sensitive taxa incur substantial damage but significant recovery was observed after a month.