Meeting Abstract
While tropical corals exist within a narrow temperature range, the scleractinian 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 algal symbiont. Eight colonies of A. poculata were collected from Naragansett Bay, RI, and fragmented into four pieces. Genetically identical symbiotic and aposymbiotic fragments were exposed to increased temperatures for three weeks. Maximum photochemical efficiency (Fv/Fm), respiration, photosynthesis, and reflectance were measured throughout the ramping period from 18 to 30°C, and during the hold at 30°C. RNAseq analyses are underway. No death was observed, thus A. poculata colonies from the northern range edge are able to acclimatize to temperatures consistent with the southern edge. However, the extreme high temperatures did damage photosystem II reaction centers in the algae, as evidenced by decreased photochemistry and maximum photosynthetic rates. Metabolic responses to extreme temperatures were genotype specific, with some host and symbiont combinations maintaining a steady respiration rate and others elevating their rates. Previous studies of coral metabolism genes under high temperature exhibited variable expression patterns, perhaps due to the influence of the algal partner. Instead, our comparison of differentially expressed genes between aposymbiotic and symbiotic fragments will differentiate the metabolic response of the coral host to thermal stress from the host response to a stressed algal partner. These results show that the thermal tolerance of the coral is higher than the symbiont, and that considering both is important when predicting the effects of climate change.
