Photophysiological stress in response to short-term sedimentation in scleractinian corals of the Great Barrier Reef

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Effects of short-term sedimentation on common coastal coral species were investigated in laboratory and field experiments on the Great Barrier Reef using pulse-amplitude modulated (PAM) chlorophyll fluorometry. In the laboratory, changes in maximal quantum yields of photosystem II (Fv/Fm) in Montipora peltiformis were examined in response to the amount of sedimentation (mg cm-²) and duration of exposure (h). Field experiments compared susceptibilities of common coastal coral species to sedimentation through examination of quantum yields.Fragments of the foliose coral M. peltiformis were sampled from 3 to 5 m water depth at Magnetic Island. Fine, muddy sediment was collected from 3 m water depth near the AIMS jetty and its carbon, nitrogen, and phosphorous levels ascertained. Corals in tanks were exposed to sediments which were stirred and allowed to settle before controls were reintroduced.Photosynthetic activity was determined by measuring variable chlorophyll fluorescence of photosystem II (PS II), with a pulse-amplitude modulated chlorophyll fluorometer. In dark acclimated corals, maximal quantum yield was calculated as the ratio of variable to maximum fluorescence (Fv/Fm). Fifteen measurements, evenly distributed over the surface, were made on each fragment.Sediment load was calculated by normalising the amount of sediment (dry weight) retrieved from each coral fragment normalised to its surface area (determined by tracing the coral outline onto paper, cutting and weighing the paper, then using a calibration curve to convert paper weight to surface area).Subsamples of the corals were analysed for zooxanthellae densities and chlorophyll (chl a and chl c2) concentrations. Two subsamples were counted under the microscope using a haemocytometer slide (8 replicates) and counts were normalised to coral surface area for zooxanthellae densities.Sediment-loaded and control fragments were removed from the tank after 0, 12, 18, 24, and 36 h and 2-5 replicates were analysed for each treatment and time. Recovery from sedimentation was monitored for up to 7 days by repeated measurements of maximum PS II quantum yields of M. peltiformis fragments, which had been exposed to sediment for 0, 12, 18, and 24 h.To determine the effects of sedimentation on adjacent tissue, sediment was applied to about 50% of the surface of 4 colonies of M. peltiformis (the remaining surface was left clean). After 48 h exposure, maximum quantum yields of the clean surfaces and those along the edge of the sediment patch, were measured and compared with those of the colonies before sediment application. The experiment was repeated on 4 colonies each of Echinopora lamellosa and massive Porites (exposed for 22 h before measurement of effective quantum yield).Sediment was added to 12 common coastal species of scleractinian corals at 6¿8 m depth on the coastal reefs PAM and chlorophyll fluorometry measurements were taken to assess the effects of 22 h of sediment loading on the effective yields. Responses were assessed between reefs and between species.
The study aimed to investigate the short-term stress reaction of the coral Montipora peltiformis to sediment exposure and its potential to recover from such stress under controlled laboratory conditions, particularly, the effects of exposure to different amounts of sediment for different lenths of time on photosynthetic activity, zooxanthellae count, and chlorophyll concentration.To assess the susceptibility of a range of coral species to sediment stress in the field. To contribute to understanding about the damage to corals caused by short-term exposure to high levels of sedimentation and potential shifts in community structure in relation to prolonged or repeated enhanced levels of sedimentation in coastal reefs of the Great Barrier Reef.
Reef locations: Hay Island and Wilkie Island (northern Great Barrier Reef), and Green Island and Normandy Island (central Great Barrier Reef).Echinopora lamellosa, Fungia crassa, Galaxea fascicularis, Montipora crassituberculata, Montipora danae, Montipora tuberculosa, Merulina scabricula, Pachyseris speciosa, Pectina lacuca, massive Porites, Turbinaria peltata, Turbinaria reniformis

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Credit
Fabricius, Katharina E, Dr (Principal Investigator)