Cassiopea xamachana was collected from the Florida Keys, Florida, USA, and the effect of sub-bleaching heat stress on percent composition of energetic components (protein, carbohydrate, lipid) under differing salinity and light conditions was measured. Jellyfish were subjected to a heat-stress event by elevating temperatures to 33°C over seven days, or no heat-stress control, and were then held for eight weeks under a salinity of 30 g kg^-1, 35 g kg^-1, or 40 g kg^-1, and either a higher or lower light exposure. A small initial sample at the end of the heat-stress event indicated no difference in zooxanthellae count. At the end of eight weeks no difference was found between heat-stress and no heat-stress treatments for zooxanthellae count, or any energetic component; however, a decrease in carbohydrate was associated with lower light exposure, and possibly the highest salinity. The results indicate Cassiopea xamachana is resilient/resistant to short-term heat-stress events, even when coupled with varying conditions of salinity and light.