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Differential Responses of a Facultatively Symbiotic Coral (Astrangia poculata) and Its Algal Symbiont (Symbiodinium psygmophilum) to Thermal Stress

Speaker: Andie Chan, Penn State University

Date and Location

When (Date/Time)

November 29, 2017, 12:20 PM - 1:10 PM

Where

104 Forest Resources Bldg.

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Ecology Grad Colloquium

The potential for sessile species to survive climate change depends in part on their ability to acclimatize to warming. While tropical corals exist within a narrow temperature profile, the scleractinian northern star coral, Astrangia poculata, extends over 11 degrees of latitude. Colonies of A. poculata are facultatively symbiotic, which provides a unique system for studying the coral host with and without the dinoflagellate Symbiodinium psygmophilum. Eight colonies of
A. poculata were collected from Naragansett Bay, Rhode Island, and fragmented into four pieces. Genetically identical symbiotic and aposymbiotic fragments were exposed to increased temperatures for three weeks. Maximum photochemical efficiency (Fv/Fm) was measured daily throughout the ramping period from 18 to 30°C, and during the hold at 30°C. Respiration, photosynthesis, and reflectance were measured every three days. Finally, RNA was extracted from all fragments and submitted for RNAseq analysis. While some host and symbiont genotype
combinations maintained a steady metabolic rate despite extreme temperatures, others elevated their respiration rates. No colony death was observed, thus indicating that A. poculata colonies from the northern edge of this species’ range are able to acclimatize to temperatures consistent with the southern edge. There was an overall decrease in photochemistry (Fv/Fm) and in the maximum photosynthetic rates (Pmax) in the symbiotic colonies that were exposed to extreme high temperatures, showing a stress response in the algae. These results demonstrate that the thermal tolerance of the coral host and symbiont differ, and that considering both is important when predicting how climate change will affect this species.