How might experiments on heat stress in corals be used to predict the response of corals to global warming?

How can we put studies like the one conducted by Rachael and her colleagues to use? One way is to use the information to make predictions. As we’ve noted in this chapter, abundant evidence shows that Earth’s climate is warming as a result of increased levels of CO₂ in our atmosphere. Can corals survive this global warming, or will they all lose their photosynthetic dinoflagellates and die? The experiments and observations done by Rachael’s team suggest that higher temperatures will lead to increased coral bleaching, but that some short-term acclimation of individuals can occur. If global warming is slowed sufficiently, longer-term processes of evolution will act on the surviving corals that have genetic adaptations that increase their tolerance to warmer waters. This selection process should result in genetic changes in populations, which will allow more corals to survive. How well acclimation and adaptation can work to ensure the survival of corals depends on many factors, including the average life span of individual corals, the rate of global warming, and the availability of alternative heat-resistant dinoflagellates. The basic research conducted by Rachael’s team is a first, but critical, step in predicting the future response of corals to global warming.

Future directions

As described, the corals in Rachael’s study have certain species of dinoflagellates growing within their cells. The corals provide a suitable environment for the dinoflagellates and the dinoflagellates provide nutrients for the corals. Such a mutually beneficial relationship is called symbiosis. The bleaching response to high temperature implies dysfunction in the dinoflagellates, leading to their expulsion from the corals. Understanding thermal tolerance of the corals therefore requires greater understanding of genetic changes and acclimation of the symbiotic dinoflagellates. Other studies have shown that some corals contain multiple strains of dinoflagellates, and these strains change in abundance when the corals are grown at different temperatures, perhaps contributing to thermal tolerance. There are many species and strains of dinoflagellates, but coral species usually are associated with specific species. Future research could focus on thermal tolerance of dinoflagellates to identify genes that confer thermal tolerance. Additional research could be to find ways of transferring those genes into other species of dinoflagellates or to find ways of infecting corals endangered by rising temperatures with strains of temperature-tolerant symbionts.