BACKGROUND

      Coral bleaching is a serious problem in coral reefs worldwide. Bleaching occurs when coral eject their symbiotic zooxanthellae and turn from tan to white. Increased water temperature, likely due to global warming in some areas, is correlated to bleaching. There are now global reef watches documenting coral bleaching events and other problems such as diseases.

      One explanation for coral die-off in the Florida Keys area is that increased turbidity of the water column (perhaps due to increased nutrients and phytoplantkon growth) results in less light reaching corals. Coral bleaching has been observed there and corals do eject their zooxanthellae under low light conditions. To understand the process of coral bleaching students must understand that the coral animal contains photosynthetic algae. This activity will help them figure that out.

      In this set of experiments, the researcher measured metabolism (changes in oxygen concentrations) by placing a clear tunnel over a 4x2m section of coral and measuring oxygen at the upstream and downstream ends. This is a modification of the upstream-downstream approach for measuring system metabolism in streams. Her goal was to assess effects of shading on coral metabolism because water column turbidity from increased sedimentation and eutrophication is a problem in some reefs.

      For coral bleaching images see http://www.reefbase.org/threats/thr_bleaching.asp, http://www.gbrmpa.gov.au/corp_site/info_services/science/bleaching/, and http://www.marine.uq.edu.au/OHG/news/.