The Upside down jellyfish (Cassiopea frondosa) live in the mangroves and sandy areas here at Discovery bay. Like many corals they have a symbiotic and mutual relationship with the dinoflagellates zooxanthallae. Zooxanthallae grows on the down side of the jellyfish and photosynthesize to provide the jellyfish with nutrients and oxygen while jellyfish in turn provides the zooxanthallae with a home near the photic zone, carbon dioxide, and protection. Corals have an obligative mutualistic relationship with their zooxanthallae ; if jellyfish have such a relationship with their zooxanthallae, the current environmental changes may be detrimental to them as well and may cause jellyfish bleaching. Thus we wanted to see what conditions may cause the Cassiopea frondosa to expel their zooxanthallae. We completed two different experiments: the effects of darkness and different salinities on the jellyfish. For the Light/Dark experiment we collected jellyfish and exposed half of them to constant darkness and the other half to ambient light. For the salinities experiment we divided the jellyfish into three different settings, one with high, one with low, and one with ambient salinity. We then counted average cell densities of all the jellyfish every 24 hours for the light/dark experiment and every few hours for the salinity experiment. We concluded that under the time constraints and the particular conditions we chose the jellyfish did not show significant expulsion of their zooxanthalle. This means that the jellyfish may not expel their zooxanthallae like the corals or the conditions they we subjected to were not extreme enough.