Oxygen and irradiance constraints on visual habitat in a changing ocean: The luminoxyscape

Abstract

Changing oxygen conditions are altering the distribution of many marine animals. Zooplankton vertical distributions are primarily attributed to physiological tolerance and/or avoidance of visual predation. Recent findings reveal that visual function in marine larvae is highly sensitive to oxygen availability, but it is unknown how oxygen, which affects light sensitivity and generates limits for vision, may affect the distribution of animals that rely heavily on this sensory modality. This study introduces the concept of a "visual luminoxyscape" to demonstrate how combinations of limiting oxygen and light could constrain the habitat of marine larvae with oxygen-demanding vision. This concept reveals the impact of sublethal climate change vulnerabilities in visual marine animals and provides an additional hypothesis for habitat compression under ocean deoxygenation, which we argue deserves attention. Climate change and species' sensitivityManifestations of climate change in the ocean, such as warming, acidification, and deoxygenation, alter the physiological and behavioral responses of marine organisms, and shift their distributions (Somero 2012). Species vulnerability to changing environments is routinely assessed using extreme physiological tolerance limits. "Hypoxia," often defined as 2 mg O 2 L À1 , $ 60 μmol kg À1 , or 5 kPa, for example, is a commonly used oxygen threshold in marine life, though it may not accurately reflect an organism's oxygen limits (Vaquer-Sunyer and Duarte 2008). Studies have used a metabolic oxygen limit, or P crit (oxygen at which an animal's metabolic rate changes), as a threshold for physiological tolerance to oxygen (Seibel et al. 2021). This limit has inspired several indices (e.g., Metabolic Index, Aerobic Growth Index) that integrate metabolic and biogeographic data to predict future changes in species' distributions by examining combinations of oxygen and temperature conditions that are suitable for metabolic function (Penn et al. 2018;Deutsch et al. 2020;Clarke et al. 2021). Here we introduce a novel concept that relates species-specific experimental visual limits to potential changes