Carnegie Science | Spring 2019 17 How much of a coral reef’s ability to withstand stress is influenced by the type of algae that the coral hosts? Corals are marine invertebrates that build large exoskeletons, which form colorful reefs. This reef building is only possible because of a mutually beneficial relationship between the coral and various species of single-celled algae called dinoflagellates, which live inside the cells of coral polyps. The algae are photosynthetic; they convert the Sun’s energy into chemical energy for food, like plants. The exchange of nutrients between the coral and the algae is essential for healthy reefs. The coral provides the algae with carbon dioxide, nitrogen, and other compounds for photosynthesis. In turn, the algae stimulate coral growth by providing them with sugars and fats created via photosynthesis. An international team based in New Zealand, which includes Carnegie’s Arthur Grossman, wanted to determine how the abundance and diversity of sugars and other carbon compounds shared with the coral varies between species of algae and whether this affected a coral’s ability to survive under stressful conditions caused by climate change. They studied the anemone Aiptasia, from the phylum Cnidarian like the coral, which can also host symbiotic dinoflagellates. But it grows faster than coral and is easier to study. Proceedings of the Royal Society B published their findings. “We’re very interested in what happens when external conditions force corals to switch from hosting one symbiotic algal species to another,” Grossman said. “Having a long-term symbiotic relationship with a native algal species is advantageous to the coral. But if the surrounding conditions are altered by climate change, could a different algal species confer corals with improved fitness and chances of survival?” When comparing the sugars, fatty acids, and other metabolic products transferred to the host anemone by two different species of algae—one native, the other not normally found in the anemone host—the team found that the native species consistently provided more nutrition to the anemone than the non-native species. However, the transplanted “poor-provider” algae used in this research, called Durusdinium trenchii, is known to have a high heat resistance, and it’s been observed to repopulate coral communities that have been damaged by bleaching and have lost their original algal tenants. “Under normal conditions, coral or anemones that host a species of algae that’s a poor nutrient provider will be forced to burn its own energy stores and take in nutrition from the surrounding water,” Grossman explained. “But in the wake of a bleaching event, even a poor provider may be better than no provider.” Further research with a greater variety of algae and observing the flow of nutrients between the organisms in greater detail is necessary to fully understand if more-heat tolerant but less- generous algal species might help these ecosystems survive a world with a rapidly changing climate.  Image 1 shows the anemone Aiptasia pallida, the model Cnidarian lacking endosymbiotic algae used for the team’s studies. Image 2 shows Aiptasia with its symbiotic algae. Image 3 shows a fluorescence image of the Aptasia; the red fluorescence is from the symbiotic algae’s chlorophyll. Images courtesy Arthur Grossman Carnegie’s Arthur Grossman Could “Poor-Providing” Algae Help Corals Recover? Healthy coral reefs burst with color, while corals lacking symbiotic algae are bleached of their brilliance (right). Images courtesy Greg Asner/Divephoto and NOAA (right) SUPPORT: The Company of Biologists’ Journal of Experimental Biology Travelling Fellowship and a grant from the Royal Society Te Apārangi Marsden Fund supported this work. 1 2 3