Acute Sedimentation Causes Size-Specific Mortality and Asexual Budding in the Mushroom Coral Fungia fungites

Brief description

Field experiments investigated the effect of acute sedimentation on polyp injury, mortality and bud production, in the mushroom coral Fungia fungites in the Dampier Archipelago. 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.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: - Study site characteristics - This experiment was conducted at an inshore reef within the Dampier Archipelago, on the north-coast of Western Australia. This reef is adjacent to the mainland and approximately 2 km in length. Much of the live coral cover is established on skeletons of massive and fungiid corals, and the remaining substrata consists of sand and sediment that can accumulate in depressions throughout the reef. Observations of sediment deposition on Fungia fungites at this site were the basis for determining the size of polyps to be used, the amount of sediment to be applied, and the duration of the experiment. Small sized polyps were between 3 and 5 cm; medium polyps between 8 and 12 cm; and large polyps between 16 and 20 cm. The low sediment treatment consisted of covering polyps with a fine layer of sediment, approximately 2 mm thick. The medium sediment treatment approximately 5 mm thick and the high sediment treatment approximately 10 mm think. Control polyp were exposed only to natural levels of background sedimentation. The duration of the experiment (20 days) was based on periods of deposition following moderate to high wind and wave activity, and was standardised for all treatments. The sediment used in the experiment was collected from a dredge spoil ground in the Dampier Archipelago, and originate approximately 5 km from the study site. It ranges from coarse silt to fine grain sand (50um - 200um), and reflected the size of sediments likely to be routinely resuspended. Analysis of the sediment confirmed that it did not contain toxicants. - Experimental procedure - A total of 180 polyps were used in the experiment, of which 60 from each size class (small, medium, large) were randomly allocated to the four sediment treatments (high, medium, low, control). Small tags (5 mm) were attached with underwater putty to the undersides of polyps for identification. Although tagging damaged the polyp at its area of attachment, the tag was quickly overgrown by translucent polyp tissue, and in no cases did injuries originate from the underside of the polyps. Polyps were randomly dispersed among a homogenous area of substratum (100 m2), and sediment was applied every second day over the 20 day period. Before the sediment was applied, any sediment on the polyps was removed, and their level of injury ranked. Injuries to polyps were quantified as 20, 40, 60 or 80% of their initial tissue area. When no living tissue was observed on a polyp then this was ranked as 100% injury. Polyps with no visible tissue (100% injury) were not classified as dead because parent tissue may have regressed into the skeleton, to later emerge as attached buds. Seven months after the sediment experiment all polyps were recensused. Levels of polyp injury were again recorded, and at this time polyps were ranked as dead if they had no visible tissue on their skeleton. The number and size of asexual buds present on polyp skeletons were also recorded.

Notes

Credit
Australian Institute of Marine Science (AIMS)

Credit
Hamersley Iron

Credit
Sigma Xi

Credit
The University of Western Australia (UWA)