Beisiegel, Kolja (2012) Coral resistance : acclimatization in photophysiology and metabolic rates of the reef building coral Pocillopora verrucosa to human land-based pollution. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 57 pp.

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Abstract

In times of global change, coral reefs face a multitude of anthropogenic stressors. Changing water quality is one of the major threats to these highly specialized, oligotrophic ecosystems and terrestrial runoff still presents the dominant pressure on local scale. However, little is known about the physiological resistance and actual acclimatization speed of scleractinian corals to human land-based pollution and eutrophication. In this study, metabolic rates (photosynthesis, photochemical efficiency, respiration) and tissue composition (chlorophyll a, total protein, biomass) of sewage-impacted, near-shore colonies of Pocillopora verrucosa were compared to non-impacted off-shore corals. Transplantation experiments between both sites revealed a significant acclimatization of colonies to new water quality within six weeks with almost no differences in metabolic performance and nutritional status compared to native corals. High concentrations of dissolved inorganic nutrients (in particular nitrate), incorporated by the symbiotic algae, caused increases in zooxanthellae growth, as reflected in enhanced areal chlorophyll a and protein. Hence, coral photosynthesis and photochemical efficiency increased in eutrophic waters. Elevated level of organic matter (live, dead or dissolved) led to an increase in polyp feeding and increased biomass as well as total protein content and stimulated zooxanthellae growth via translocation of nutrients. A high energy gain via autotrophy, in addition to good nutritional supply by heterotrophy seems to compensate lower light intensity and higher sedimentation stress. However, high zooxanthellae loaded specimens from near-shore appeared to be more susceptible to changes in water quality and displayed a slower acclimatization as well as several bleaching spots in response to oligotrophic off-shore conditions. In conclusion, trophic plasticity and the physiological acclimatization potential of P. verrucosa enable the coral to convert a potential stress factor into a resource, actually benefiting from nutrient supply caused by sewage inlet. These results demonstrate the ability of some coral species to acclimatize quickly and entirely, however, it remains an open question, if these corals are also able to buffer or acclimatize to global change related stressors (e.g. SST rise), or if they might even be more susceptible.

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