THE SYNERGISTIC ROLE OF OXYGEN AND TEMPERATURE IN DEFINING AEROBIC SCOPE: PHYSIOLOGICAL IMPLICATIONS FOR PAST AND FUTURE OCEANS

A growing body of multi-proxy geochemical evidence supports increasing atmospheric and oceanographic oxygenation during the Proterozoic to early Paleozoic. Understanding how these dynamic marine redox landscapes may have affected the evolution and ecosystem structure of early metazoans ultimately requires further comprehension of how respiration physiology in modern animals responds to multi-stressor factors such as temperature and oxygen at regional oceanographic scales. Considering the modern, one of the many consequences of anthropogenic climate change is the warming and subsequent deoxygenation of Earth’s oceans, which poses a major ecophysiological threat to marine life, especially ectotherms that must either shift their habitat ranges or go extinct. Importantly, increased temperature is traditionally considered to limit aerobic scope unidirectionally by raising metabolic rates beyond the capacity of the animal to take up oxygen from its surrounding environment. Using standard respirometry protocols applied to a wide range of intertidal invertebrates we measure the oxygen- and capacity-limited thermal tolerance of these taxa and find that absolute oxygen tolerance between these groups is uneven, and varies systematically across annual temperature ranges both above and below a taxon-specific temperature optimum. These results have significant implications for modern global change biology, as habitat viability in decreasing oxygen conditions may be significantly more complex than previously considered. This methodology may also inform studies aimed at integrating fossil and paleoenvironmental records through the lens of physiology, particularly for Proterozoic and early Paleozoic oceans characterized by low and dynamic ambient oxygen partial pressures, as well as episodes of extreme climate fluctuations towards global ice- and green-house conditions.