Ideas and perspectives. The fluctuating nature of oxygen shapes the ecology of aquatic habitats and their biogeochemical cycles: the aquatic oxyscape
Abstract. Oxygen availability is a pivotal factor for ecosystem functioning and the resistance of organisms to the effect of climate change in aquatic habitats. Although extensive work has been made to assess the effect of oxygen on marine and freshwater biota, many studies did not capture the ecological importance of oxygen variations. Overlooking the fluctuating nature of oxygen may cause potential biases in the design and implementation of management policies of aquatic habitats. Conceptual perspectives on the dynamic nature of oxygen fluctuations have been raised in the scientific community to enhance the understanding of the effect of oxygen on the physiology and the ecology of aquatic species and the biogeochemical functioning of the ecosystems. A growing number of empirical works are outlining a novel conceptual framework that considers the magnitude of oxygen fluctuation as a key variable that explains adaptation to stress conditions. Oxygen in productive aquatic habitats shows large fluctuations at diel and seasonal scales, exposing aquatic species from conditions of extreme supersaturation to anoxia. Recent research indicates that such fluctuation tunes the physiological plasticity of the animal in response to thermal stresses. In this contribution, we provide compelling evidence based on current research that the fluctuating oxygen landscape, here defined as “oxyscape”, has an important role in aquatic animal physiology and adaptation and the ecosystem biogeochemistry. We propose that the oxyscape should be considered in the modelling and managing policies of aquatic ecosystems.
Marco Fusi et al.
Status: open (until 14 Apr 2023)
- RC1: 'Comment on bg-2023-45', Anonymous Referee #1, 16 Mar 2023 reply
Marco Fusi et al.
Marco Fusi et al.
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The authors have assembled a nice review of high frequency variation in dissolved oxygen (DO) and the potential causes and consequences. I suggest that the manuscript would be improved if the focus was on DO variation in just coastal environments rather than including both coastal and open ocean examples. The inclusion of both leads to some confusion; for example, on lines 68-69 the authors state (from references) that short-term DO variation is greater than seasonal. While this may be true for shallow coastal environments it is not universal in continental slope or open ocean waters. Note on lines 77-78 the authors quote a gradual 2% reduction in the ocean (global average) DO with possible further decrease of 7%. The shallow systems they highlight in Figure 1 may have had reductions in DO more than these global averages. The point is with the exception of Figure 3 (which could be eliminated) all of their examples of high frequency variation in DO are from coastal systems and many of these are shallow systems where sedimentary processes can drive water column DO. Thus, if they focus on just coastal systems the paper would not have open ocean examples that do not apply to shallow coastal systems.
Line 113: Water residence time and oxygen input through 2-layered gravitational flow will also impact oxygen fluctuations. In general, I suggest that the authors could have included more physical mechanisms that support or negate high frequency DO fluctuations. Is DO variation highest in shallow waters that do not have a density stratification? How does water residence time influence DO variation? Will there be more short-term variation in DO if > 1% surface irradiance reaches the bottom? These physical drivers might be used to be able to predict coastal environments that are likely to have large short-term variations in DO.
Lines 354-360. I suggest that it is not necessary to point out spatial variability for this example, when most all of the phenomenon discussed have inherent spatial scales of variability. The focus of this paper is high frequency temporal variability.
One topic to include in the management section is that oxygen criteria (minimum oxygen concentration tolerated by commercially important species) developed by environmental regulatory agencies should include not just “average” DO conditions but also the minimum values measured with high frequency sampling as shown in their Figure 1.