Understanding eastern oysters (<i>Crassostrea virginica</i>) thermal and hypoxia tolerance: A systematic review of biological responses

The eastern oyster (<i>Crassostrea virginica</i>) is a key contributor to estuarine and marine ecosystem structure and function and supports fisheries and aquaculture across its wide geographic range. Temperature and dissolved oxygen (DO) are two major abiotic factors influencing oyster physiology, survival, and overall distribution. Thermal and hypoxia tolerance can be assessed by observing the biological endpoints, such as mortality and growth, which reflect cumulative physiological constraints, alongside physiological and biochemical responses that provide mechanistic insight into why tolerance limits are reached. This systematic review synthesizes the current scientific knowledge on the thermal and hypoxia tolerance of eastern oysters, drawing on 78 studies selected using the PRISMA methodology, with searches from the Scopus, Biological Abstracts, and Earth, Atmospheric & Aquatic Sciences databases. The biological responses assessed include survival, growth, metabolic rate, heat shock protein expression, and anaerobic end product accumulation. The reviewed literature shows that oyster tolerance is context-dependent, varying with study conditions, life stage, season, reproductive status, and prior environmental exposure. Despite this variability, oysters can generally cope with a wide range of temperatures and DO concentrations, with exposure duration emerging as the most critical variable in determining the specific threshold. A hierarchical pattern was also observed across levels of biological organization, whereby higher-level endpoints and responses, including survival, growth, and metabolic rate, exhibited higher temperature limits than the biochemical responses. By synthesizing patterns of biological responses, this work provides insights into tolerable temperature and oxygen ranges, factors that modify tolerance, and biological indicators for the onset of stress.