Using Modern Microscopy to Illuminate Coral Bleaching

neil blackstoneNeil Blackstone
Department of Biological Sciences




Project Description: Coral bleaching presents a major threat to a considerable portion of the ocean’s biodiversity. When bleaching in response to excess temperature, light, or other environmental factors, corals initiate a stress response that typically involves the loss of photosynthetic dinoflagellate symbionts. Loss of these photosynthetic symbionts negatively impacts coral fitness, productivity, and ultimately the coral reef habitat. In the context of climate change, coral bleaching has attracted considerable attention, both from scientists and from the popular media. Despite this attention, no general consensus exists as to how the process of bleaching initiates. While no doubt damage to the photosynthetic apparatus of the symbionts is involved, most hypotheses implicate either the initial step (the D1 protein that extracts electrons from water) or the terminal step (the RuBisCO protein that fixes carbon dioxide).

Progress in this regard has been hindered by two factors.  First, corals are typically studied in the field where the range of experimental techniques is limited (e.g., the power of modern microscopical techniques cannot be applied).  Second, damage to the photosynthetic apparatus is usually assessed in terms of the “quantum yield” of light, which can produce similar values without regard to where the damage is actually occurring. Using octocorals, we have developed laboratory models to study coral bleaching. While octocorals do not build reefs, they are nevertheless a major component of the diversity of these reefs. They are also fast growing, relatively durable, and can be studied with fluorescent microscopy. This latter technique allows us to examine the relative fluorescence of the photosystems in symbionts from bleached and unbleached corals. Thus the differential hypotheses can be tested, e.g., in bleached versus unbleached controls, if D1 is damaged, the photosystems will be relatively oxidized (less fluorescence), while if RuBisCO is damaged, the photosystems will be relatively reduced (more fluorescence). In this context, the summer REU student will carry out experiments on photosystem fluorescence in one or more of our model species, including culturing coral model organisms, performing image analusis, and statistical data analysis.