The effect of sudden changes in temperature, light and salinity on the population density and export of zooxanthellae from the reef corals Stylophora pistillata Esper and Seriatopora hystrix Dana

摘要: Abstract Bleaching (loss of pigmentation by corals) is a widespread phenomenon in coral-reef ecosystems. Despite this, the underlying causes some forms bleaching are poorly understood. This study explores conditions that induce two species reef coral-zooxanthellae associations from Lizard Island, Great Barrier Reef, Australia. Naturally bleached Stylophora pistillata Esper and Seriatopora hystrix Dana, collected edge Island lagoon, had same amount Chl · zooxanthellae −1 , yet reduced population densities when compared to normal-looking colonies. In this case, lack pigment corals was explained low numbers not pale zooxanthellae. contrary results obtained other workers suggests closer inspection reasons for color warranted. laboratory experiments, sudden exposures full sunlight induced S. previously grown at 25% sunlight. The colonies exposed content rather than addition, specific expulsion rate Pistillata influenced increases solar irradiance. Sudden salinities (30%.) did affect or study. Both rapidly, however, water temperatures > 30 °C. Bleached case despite normal zooxanthella contents. both coral very sensitive temperature. 7-h 32 °C resulted rates 1000 times controls. Specific remained high, even were returned control (27 °C). After high temperature stress, sustained colony respiratory ( r c ), photosynthetic p net max ) P g : ratios. O 2 metabolism symbioses abnormal up 4 days after exposure Evidence suggestive recovery apparent 19 later. By time, mean density ratios fragments normal.