Integrative Approaches to Understanding Organismal Responses to Aquatic Deoxygenation

Abstract

Oxygen bioavailability is declining in aquatic systems worldwide as a result of climate change and other anthropogenic stressors. For aquatic organisms, the consequences are poorly known but are likely to reflect both direct effects of declining oxygen bioavailability and interactions between oxygen and other stressors, including two-warming and acidificationthat have received substantial attention in recent decades and that typically accompany oxygen changes. Drawing on the collected papers in this symposium volume ("An Oxygen Perspective on Climate Change"), we outline the causes and consequences of declining oxygen bioavailability. First, we discuss the scope of natural and predicted anthropogenic changes in aquatic oxygen levels. Although modern organisms are the result of long evolutionary histories during which they were exposed to natural oxygen regimes, anthropogenic change is now exposing them to more extreme conditions and novel combinations of low oxygen with other stressors. Second, we identify behavioral and physiological mechanisms that underlie the interactive effects of oxygen with other stressors, and we assess the range of potential organismal responses to oxygen limitation that occur across levels of biological organization and over multiple timescales. We argue that metabolism and energetics provide a powerful and unifying framework for understanding organism-oxygen interactions. Third, we conclude by outlining a set of approaches for maximizing the effectiveness of future work, including focusing on long-term experiments using biologically realistic variation in experimental factors and taking truly cross-disciplinary and integrative approaches to understanding and predicting future effects.

Temperature and hypoxia‐driven shifts in Daphnia interspecific competition

“…In conclusion, the potential interactions between temperature and hypoxia in terms of their biological effects have received limited attention, despite their recognized importance in aquatic ecosystems (Roman and Pierson 2022; Woods et al 2022; Verberk et al 2022). The aim of this study was to investigate their impact on the interspecific competitive abilities of different‐sized Daphnia species.…”

Responses of intraspecific metabolic scaling to temperature and activity differ between water‐ and air‐breathing ectothermic vertebrates

“…Besides measures to improve oxygen-supply capacity at increased temperatures as water-breathers grow (e.g. Funk et al, 2021;Nilsson et al, 2012;Woods et al, 2022), oxygen demands may be reduced. Metabolic costs are not just from tissue maintenance, but also include overhead costs of growth, which contribute strongly to metabolic rate (Parry, 1983), even in individuals that are resting and postabsorptive (Rosenfeld et al, 2015), as most measurements compiled in our data sets.…”

Long‐term forecast of thermal mortality with climate warming in riverine amphipods

“…A mismatch between oxygen supply and demand has been proposed to explain thermal limits; as water temperatures rise, metabolic demand for oxygen increases, eventually exceeding the capacity of an organism to supply its tissues with sufficient oxygen (Pörtner, 2010). Whether or not oxygen limits heat tolerance under normoxia is debated (Jutfelt et al, 2018; Pörtner et al, 2017; Verberk, Overgaard, et al, 2016), but hypoxia is widely acknowledged to amplify the detrimental effects of warming (Woods et al, 2022). This includes reductions in heat tolerance under hypoxia which have been reported for a range of aquatic ectotherms including crustaceans, insects, mollusks, and fish (Ern et al, 2016; Healy & Schulte, 2012; Koopman et al, 2016; Rutledge & Beitinger, 1989; Verberk & Bilton, 2013; Verberk, Leuven, et al, 2018).…”

“…Therefore, the combined effect of heat stress and low oxygen levels can negatively impact the fitness and geographical distribution of aquatic ectotherms (Deutsch et al, 2008; Ern, 2019; Verberk, Overgaard, et al, 2016). This is especially alarming, given the widespread deoxygenation of aquatic ecosystems and its interactions with global warming and eutrophication (Breitburg et al, 2018; Jane et al, 2021; Woods et al, 2022).…”