Corals Need Their Vitamins Too: The Effect of Antioxidants on the Coral Bleaching Response

Danielle Twum, Vassar College '12, Ishaira Nieto-Rosas, Vassar College '14 and Prof. Jodi Schwarz

Coral reefs are complex and fragile communities that serve as a source of food and habitat for marine organisms. Most corals form a mutualistic symbiosis with unicellular dinoflagellate symbionts, in which the relationship is founded on reciprocal feeding. The coral feeds the symbiont inorganic waste materials like nitrogen, phosphorus and carbon and the symbiont in turn transforms these products into photosynthates and transfers it back to the host coral. When exposed to elevated temperatures, corals respond by "bleaching," which is a breakdown in the symbiotic relationship. Evidence suggests that thermal stress induces a strong bleaching response by disrupting the photosynthetic functioning of the symbiont, producing an excess of reactive oxygen species (ROS). The presence of ROS triggers an oxidative stress response in the host, leading to cellular damage. Therefore, bleaching is the end result of an oxidative stress response in corals. We hypothesized that exposure to an antioxidant compound should mitigate or reduce the severity of bleaching. Aiptasia pallida is a sea anemone with the same symbiosis as corals, and is an ideal model system for studying bleaching. We designed an experiment in which anemones were exposed to thermal stress in different concentrations of Naringin dihydrochalcone, an antioxidant compound. We measured the severity of bleaching by comparing the number of symbionts in anemones maintained in different treatments. The data indicated that although the antioxidant did not completely prevent bleaching, it reduced the severity of the bleaching response significantly.