Photophysiological stress in scleractinian corals in response to short-term sedimentation

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Effects of short-term sedimentation on common coastal coral species were investigated inlaboratory and field experiments on the Great Barrier Reef (GBR) using pulse-amplitude modulated(PAM) chlorophyll fluorometry. In the laboratory, changes in maximal quantum yields ofphotosystem II (Fv/Fm) in Montipora peltiformis were examined in response to the amount ofsedimentation (79&#8211;234 mg cm-2) and duration of exposure (0&#8211;36 h). In control colonies, Fv/Fmranged from 0.67 to 0.71, and did not show any temporal trend, while maximum yields ofsediment-covered fragments declined steadily and reached levels below 0.1 in most colonies after36 h coverage. Maximal quantum yield in M. peltiformis declined linearly in relation to both theamount of sediment deposited per unit surface area and the duration of exposure. Zooxanthellaedensities and chlorophyll concentrations per unit area of sediment-treated corals decreased in thesame manner, however, their responses were not quite as strong as the changes in Fv/Fm. Withinthe ranges measured, sedimentation stress of colonies exposed to large amounts of sediment forshort periods of time was similar to that exposed to low amounts of sediments for prolongedperiods of time. Colonies were recovered from short-term, or low-level, sedimentation within <36h, whereas long-term exposure, or high levels of sedimentation, killed exposed colony parts. Fieldexperiments comparing susceptibilities of common coastal coral species towards sedimentationshowed significant reductions in effective quantum yields (F/Fm') in 9 out of 12 common coastalspecies after 22 h of exposure. Three out of twelve investigated species were not affected by theexperimental application of sediments (Galaxea fascicularis, Fungia crassa, and Pectinialactuca). Our results suggest that anthropogenic sediment deposition can negatively affect thephotosynthetic activity of zooxanthellae and thus the viability of corals. However, the results alsoshowed the ability of corals to compartmentalise sedimentation stress, as the photosynthetic activityonly from tissues directly underneath the sediment declined, whereas that of adjacent clean tissuesdid not change measurably.

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Philipp, E. and Fabricius, K. (2003): Photophysiological stress in scleractinian corals in response to short-term sedimentation , Journal of experimental marine biology and ecology, 287 , pp. 57-78 .

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