Chapter 4 Oxygen and Capacity Limited Thermal Tolerance

Abstract

Temperature and hypoxia would traditionally be considered as different environmental factors, with specific implications for whole organism functioning. Development of the concept of oxygen and capacity limited thermal tolerance in marine water breathers has revealed how these factors are intertwined. Thermal stress causes systemic hypoxemia and the interaction of temperature and thermally induced hypoxemia will thereby shape acclimation responses at various molecular to whole organism levels. The chapter discusses aspects such as temperature‐dependent oxygen supply, width of thermal window and associated energy budget, hypoxemia related stress, and signaling, as well as the cellular mechanisms of thermal adaptation and associated costs including handling and role of calcium. The integration of these responses supports adjustment of metabolic and functional performance at cellular, tissue, and whole organism levels to within thermal limits. Thereby, processes involved in thermal acclimatization and adaptation counteract thermally induced hypoxemia in fish. Conversely, hypoxia and other stressors will affect thermal tolerance limits and the processes involved in thermal acclimatization and adaptation. As a perspective, the specialization of whole organism functioning on limited temperature ranges emerges as a key element explaining current observations of climate change effects on ecosystems.