Rice, E., Que, K., Tulioc, S., Steele, J., Coelho, V. R.

Possible mitigation of coral bleaching using shading in conditions of cumulative thermal stress in Acropora aspera

2014

Twenty-eighth National Conference on Undergraduate Research (Abstracts), April 3-5, 2014, Lexington, Kentucky

"Global climate change is increasing the amount of thermal stress in coral reefs, which can lead to bleaching events and widespread coral mortality. During bleaching, corals become pale or white because of the expulsion of their algal symbionts, which are responsible for most of their hosts color. In addition to high temperatures, corals are also stressed by high light intensities. In this study we investigated the possibility of using shading as a means to decrease the overall stress of Acropora aspera corals in higher than normal seawater temperature conditions. A total of 313 corals originally from American Samoa, were kept in 10 aquaria, each with 30-32 specimens about 5-10 cm tall. Water quality in all tanks were monitored daily. The control tanks included two aquaria at 26 degrees Celsius, and two at 29 degrees Celsius. All other aquaria were kept at 31 degrees Celsius; two of them were not shaded, and the other four were shaded at Degree Heating Week (DHW) 01 (as described in the methodology designed by the Coral Reef Watch Satellite Bleaching Alert System, developed by the National Oceanic and Atmospheric Administration). Among the shaded tanks, two of them received 50 percent reduction and the other two received 75 percent reduction in light intensity. The temperature in the aquaria was recorded every 10 minutes using loggers, and cumulative thermal stress was calculated daily until the end of the experiment where the tanks reached DHW 08 (approximately 34 days). Photographs of the corals were taken every DHW and were analyzed using a standard color scale (Coral Health Chart by CoralWatch, University of Queensland). At the start of the experiment all aquaria had similar mean color shade between 4.3 and 4.5, but after DHW 01 all non-control corals were starting to pale. Among the thermally stressed corals; shaded ones remained darker than non-shaded corals from DHW 02 to 05, but corals under 75 percent shade paled more rapidly than corals at 50 percent shade starting at DHW 03. After DHW 06, shading was no longer statistically effective in preventing bleaching in corals under thermal stress. Control corals remained darker than all others for the duration of the experiment. Based on our results we concluded that by reducing irradiance, coral bleaching can be attenuated in conditions of cumulative thermal stress in Acropora aspera, and that 50 percent shading is more effective than 75 percent shading."

NOAA award NA09NMF4630105

NA09NMF4630105