Comparing physiological responses to hot and cold stress in a cnidarian–algal holobiont, \u3ci\u3eExaiptasia diaphana\u3c/i\u3e

Coral bleaching—the breakdown of the cnidarian–algal symbiosis—is a major cause of reef decline. The sea anemone Exaiptasia diaphana, commonly known as Aiptasia, is used as a model to study cnidarian-algal symbiosis in laboratory settings. Aiptasia can live with or without symbionts, which allows scientists to study the host combined and separate from the influence of the symbionts. Scientists are able to trigger the breakdown of the symbiosis using heat or cold stress. Cold stress is more commonly used to render aposymbiotic Aiptasia because it seems to be less harmful to the host than bleaching under heat stress. Is cold really less harmful than heat stress? We compared hot and cold stress responses to different stress regiments: a gradual temperature change, a gradual temperature change followed by a sudden temperature change, and a sudden temperature change from ambient conditions. We explored multiple physiological responses of the anemones to determine their level of stress response. We measured mortality and algal density in the host, as well as carbohydrate in the host and symbiont fractions. We also measured peroxide production in algal cultures exposed to the same treatment regimes. After repeating the experiment twice, we found that anemones had different responses, which emphasizes the necessity for repeated experiments in research conducted with live subjects