Luhtasela, Ulla creator Preeda Pakpian Chairperson Hansa Chansang Examination committee Jutamaad Satayavivad Examination committee Nguyen, Cong Thanh Examination Committee European Union, PTS Programme Scholarship donor text series technical report th Bangkok Asian Institute of Technology 2001 continuing eng 84 leaves Cyanide fishing is an illegal fishing method widely used in a number of countries in Southeast Asia. It is used to stun the fish to make them easier to catch. As this deadly poison spreads around the coral reef, it has an adverse impact on marine life, including fish, corals and other invertebrates. Initial, high concentration of sodium cyanide (NaCN) is known to kill coral polyps. As the cyanide dilutes and spreads around the reef, corals are exposed to low concentrations of free cyanide for prolonged periods of time, causing chronic effects. In this experiment, corals were exposed to NaCN in two concentrations (10-5 and 10-6 mol/l) for 6 hours and given 2 weeks recovery period after the exposure. Treatment was repeated twice in this experiment. Changes in chlorophyll - a and -c2 concentrations and zooxanthellae density were measured in the laboratory. Bleaching is the discoloration phenomenon of stressed corals. It can be caused by the loss of symbiotic algae, chlorophyll concentrations or both together. No significant changes were found in zooxanthellae densities after any treatments, indicating that the selected coral species, Porites lutea does not expulse its symbiotic algae from its tissue at these concentrations and duration of cyanide exposure. Significant changes of chlorophyll - a and -c2 concentrations were found in a group a (10- 5 mol/l) immediately after both exposures. After 2 weeks of recovery, concentrations returned to normal levels as compared with the control groups. Group b (1 o6 mol/l) did not show any significant changes in either of the analysis. Cyanide fishing has a high potency to stress large coral reef areas, as the initial, used concentration can be up to 1010 times higher than the studied concentration. Environmental parameters, such as pH, temperature, solar radiation, and current velocities determine the severity of the damage caused by cyanide fishing activities. A thesis proposal submitted in partial fulfillment of the requirements for the degree of Master of Science. Inter-university Program on Environmental Toxicology, Technology and Management, School of Environment, Resources and Development Thesis (M. Sc.) - Asian Institute of Technology, 2001 Cyanides Corals Environmental aspects Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B08380 http://203.159.5.9/ait-thesis/detail.php?q=B08380 020201 20260818094917.0