Coral cover is declining at an alarming rate, and it is estimated that 60% of reefs worldwide may be lost by 2030. Elevated seawater temperatures and ocean acidification are contributing to an increase in the frequency and severity of bleaching events. These events disrupt the symbiosis between corals and their photosynthetic dinoflagellates (Symbiodinium spp). Relatively little is known about the ability of corals to acclimatize to changing environmental conditions or whether the rate of climate change is too fast for corals to keep up, limiting the accuracy of future predictions for reef resilience. However, the ability of some coral species to acclimatize to elevated seawater temperatures has been linked to Symbiodinium composition and the flexibility of these associations. This study compares Symbiodinium communities and the rates of photosynthesis of two coral species, Acropora loripes and Platygyra daedalea, under three conditions of water temperature and pCO2: ambient, predicted levels for 2050, and predicted levels for 2100. Pulse amplitude modulated (PAM) fluorometry, which measures chlorophyll fluorescence, was used as an indicator of photosynthetic rate. Photosynthetic rates of A. loripes and P. daedalea differed significantly, and PAM yields were reduced in the 2050 and 2100 treatments, suggesting a stress response. The majority of genotypes of both coral species hosted clade C-type Symbiodinium suggesting that sub-type differences or host physiology may be involved in species-specific differences in photophysiology. Sequencing-based methods for Symbiodinium typing would help distinguish these possibilities and increase understanding of the influence of Symbiodinium type on photosynthetic rates of corals under changing environmental conditions.
Ecology and Evolutionary Biology | Environmental Health and Protection | Marine Biology | Terrestrial and Aquatic Ecology
Howe-Kerr, Lauren, "Symbiont type and photophysiology of Acropora loripes and Platygyra daedalea under future scenarios of rising ocean temperatures and pCO2" (2016). Independent Study Project (ISP) Collection. 2304.