Does photosymbiosis reduce physiological tolerance to temperature? An experimental and comparative approach in Octocorals

• Grant number: 22/13569-0
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: February 01, 2023
• End date: January 31, 2024
• Field of knowledge: Biological Sciences - Zoology - Physiology of Recent Groups
• Principal Investigator: Samuel Coelho de Faria
• Grantee: Letícia Guerreiro Pinheiro
• Host Institution: Centro de Biologia Marinha (CEBIMAR). Universidade de São Paulo (USP). São Sebastião , SP, Brazil

Abstract

Coral and octocoral bleaching is characterized by the breakdown of the symbiotic relationship between animal host and endosymbiont photosynthetic microalgae, so-called zooxanthellae. This phenomenon is mainly related to thermal stress conditions responsible for increasing reactive oxygen species (ROS) production by the photosynthetic machinery; ROS then spread to animal tissue, exceed host antioxidant capacity and cause, as a result, molecular damage to the coral. As a defense mechanism, corals expel the zooxanthellae, revealing the white color of the adjacent skeleton. Under the context of climate change, an increase of ocean temperature up to 4.5 °C by 2100 (IPCC, 2014) could lead to bleaching and death of several coral reefs. Thus, in a moderate predictive scenario (+3.5 oC, 14 days), we aim here to characterize octocoral metabolic physiology - a group in which energy and oxidative biochemistry are completely unknown - in order to test whether (i) high temperatures promote oxidative stress and reduce energy efficiency, and whether (ii) zooxanthellate species show lower physiological tolerance to temperature according to the premise of higher ROS production by the photosynthetic machinery of coral symbionts. Therefore, azooxanthellate octocorals would show a greater physiological tolerance to climate change when compared to photosymbiotic representatives. Clarifying these issues will broaden the scientific community's horizons about the consequences of climate change in octocorals, and will provide a comparative overview of physiological health in animals with and without photosymbiosis under the context of global warming.