Comparison of molecular biomarkers within and across scleractinian coral species exposed to elevated temperatures (Hawaii).

摘要

There has been an increase in the frequency and intensity of bleaching events on scleractinian corals since 1980. Coral bleaching in 1998 was the most extensive and severe ever recorded. These large scale bleaching episodes can result in up to 100% mortality in some areas, and major bleaching events are predicted to increase in frequency over the next few decades as a result of increasing temperatures from global warming. Many coral species are living close to their thermotolerance limits and it is unclear if corals will be able to survive further increases in mean sea surface temperatures. Will certain species suffer high levels of mortality that could drive them to extinction, and which species will acclimate to these changes? This research compares thermotolerance levels between (Pocillopora damicornis and Pocillopora meandrina) and looks at the acclimation potential of P. meandrina to elevated temperatures.; Colonies of P. damicornis from Kaneohe Bay, Hawaii, and colonies of P. meandrina from a thermal outfall site and a control site at Kahe with normal ambient sea surface temperatures, were exposed to different temperatures. Temperatures at the outfall site were up to 5°C higher than the surrounding water. Not only did this allow for comparison of thermotolerance between the 2 species, but comparisons for acclimation potential could be made between P. meandrina colonies from the thermal outfall and the control site. Several molecular biomarkers were evaluated during this research to assess photosynthetic efficiency in the zooxanthellae and antioxidant levels in the coral host. In 2002, the Ferric Reducing/Antioxidant Potential Assay (FRAP) was adapted to be used with corals to measure antioxidant levels in the coral. In 2003, Enzyme Linked Immunosorbent Assays (ELISAs) using catalase antibodies were used along with FRAP to corroborate the results from the FRAP method, since FRAP measures not only antioxidants in a sample but also chemical reductants which could have no antioxidant activity. ELISAs using several other antibodies were performed also to examine different cellular parameters that could be related to stress. Photosynthetic efficiency was measured using Pulse Amplitude Modulated (PAM) Fluorometry to measure damage to Photosystem II in the chloroplasts of the zooxanthellae.; The combined results of this research show that P. meandrina from the outfall site can tolerate elevated temperatures better than conspecifics from a nearby control population. This could be the result of acclimation to higher temperatures found near the thermal outfall. Pocillopora meandrina is regarded as one of the more thermosensitive species on Hawaiian reefs. The reactions of P. meandrina from the outfall are similar to P. damicornis, which is adapted to shallower environments with greater fluctuations in temperature and irradiance. Acclimation of P. meandrina to the conditions at the outfall site has occurred in less than 30 years. This might suggest that some coral species will be able to acclimate to the present trends in global warming after initial episodes of mass mortality, which could be already occurring on reefs around the world.