TITLE: The Role of Oxygen in Shaping Coral Thermal Tolerance

PRESENTER: Anieka Parry

ADVISOR: Professor Carlos M. Duarte

DATE: 24 Nov, 2025

TIME: 10:00 AM – 11:00 AM

LOCATION: Auditorium between Bldgs 2 & 3

Abstract: As global climate change accelerates in the Anthropocene, coral reefs are among the ecosystems most threatened by rapid degradation. Understanding the mechanisms of the breakdown of the coral-algal symbiosis and implementing interventions is becoming a matter of urgency. This thesis investigates the role of oxygen in shaping the thermal tolerance of these symbiotic organisms. Firstly principles from metabolic theory were used to quantify the temperature at which coral metabolism becomes net heterotrophic, and metabolic oxygen demand outpaces net photosynthesis using a global dataset of metabolic rates from the literature. It was found that the thermal optima for aerobic respiration (30.5 ± 1.8 °C), is higher than that of net photosynthesis (29.2 ± 1.4°C), leading to a potential oxygen deficit at temperature extremes. Secondly, Red Sea corals were exposed to an acute thermal stress regime under varying oxygen concentrations to critically evaluate whether oxygen can shift the thermal threshold of reef-building corals. Galaxea fascicularis and Acropora hemprichii showed small but detectable differences between high oxygen and deoxygenated treatments, indicating that they are able to utilize excess oxygen availability from the environment in periods of extreme heat stress. And thirdly the thermal threshold of one of the deepest photosynthesizing scleractinian corals from the lower mesophotic zone ( > 60m) was assessed and found to be highly thermally resistant (LT50 = 34.3 °C) despite an average in situ temperature of 23.8 °C (± 0.2 °C). These results challenge the notion that tropical reef building coral species are living close to their limits. Overall, the results of this PhD point to a critical role of oxygen availability in shaping thermal tolerance and highlight the importance of reducing local stressors that may exacerbate the negative effects of warming and hinder coral recovery after bleaching events.

Bio:
Anieka Parry is an PhD candidate in the Tarek Ahmed Juffali Research Chair for Red Sea Ecology lab, under the supervision of Distinguished Professor Carlos M. Duarte. She is an ecophysiologist working primarily on the effects of global change on of benthic primary producers in the Red Sea. She aims to answer questions related to this topic through a combination of experimental manipulations and large-scale data syntheses.