Declining food availability and habitat shifts drive community responses to marine hypoxia

Abstract

Worsening marine hypoxia has had severe negative consequences for fish communities across the globe. While individual­ and population­level impacts of deoxygenation have been identified, it is unknown how they interact to drive changes in food webs. To address this, we incorporated several major impacts of hypoxia, including declines in benthic re­ sources, habitat shifts, increasing mortality, and changes to rates of feeding, assimilation, and reproductive efficiency, into an existing size spectrum food web modeling framework. We used this structure to ask the following questions: which of these direct effects are most critical to capturing population and community dynamics in a representative hypoxic system, how do they interact to result in community responses to deoxygenation, and what are the potential consequences of these effects in the context of accelerating deoxygenation? We tested the effect of different combinations of oxygen­dependent processes, driven by observed oxygen levels, on the food web model’s ability to explain time series of observed somatic growth, diets, biomass, and fishery yields of commercially relevant species in the Baltic Sea. Model results suggest that food availability is most critical to capturing observed dynamics. There is also some evidence for oxygen­dependent habitat use and physological rates as drivers of observed dynamics. Deoxygenation results in declining growth both of benthic and benthopelagic fish species, as the latter are unable to compensate for the loss of benthic resources by consuming more pelagic fish and resources. Analysis of scenarios of ideal, declining, and degraded oxygen conditions show that deoxygenation results in a decline in somatic growth of predators, an altered habitat occupancy resulting in changing species interactions, and a shift in energy flow to benthopelagic predators from benthic to pelagic resources. This may have important implications for management as oxygen declines or improves.

Metabolic prioritization of fish in hypoxic waters: an integrative modeling approach

“…Dynamics ultimately emerge at the population and community levels, making the SSM an ideal method by which to understand how responses to stressors across biological levels of organization are connected. In a recent study, Duskey et al (2023) used a SSM to explore how individual vulnerability to hypoxia may lead to observed community structure using the Baltic Sea as a case study. They showed that prey availability and habitat use are critical components structuring fish community responses to hypoxia.…”

“…While it is possible that fish escape hypoxic waters before they incur significant physiological costs, there is direct evidence that hypoxic waters impact fish physiology in the Baltic Sea (Limburg and Casini, 2019). Furthermore, Duskey et al (2023) made the simplifying assumption that all physiological and behavioral activities decline in response to hypoxia at the same rate. Thus, individuals in the model were not able to prioritize among these activities.…”

“…Here, I used both a SSM and a meta-analysis to explore evidence for metabolic prioritization in fish communities. For the SSM, I used the same model structure and data sources found in Duskey et al (2023). In contrast to this study, I allowed for metabolic prioritization by relaxing the assumption that all physiological and behavioral activities decline with oxygen at the same rate.…”

“…In contrast to this study, I allowed for metabolic prioritization by relaxing the assumption that all physiological and behavioral activities decline with oxygen at the same rate. In order to test this new model's predictive capabilities relative to those of the model in Duskey et al (2023), I calibrated it to reflect the same community of commercially important fishes in the Central Baltic Sea: Baltic cod (Gadus morhua), flounder (Platichthys flesus and the recently discovered Platichthys solemdali), sprat (Sprattus sprattus), and Atlantic herring (Clupea harengus). While some were ignored, the Baltic Sea is overall a species poor system (Bonsdorff, 2006), and those included represent the dominants.…”

Mechanisms of acclimation to chronic intermittent hypoxia in the gills of Largemouth bass (Micropterus salmoides)

“…However, water hypoxia has become increasingly prevalent and severe in freshwater and marine ecosystems in the last past few decades due to factors such as the global warming, nutrient inputs, and intensive sh farming (Denise et al, 2018;Schmidtko et al, 2017;Tellier et al, 2022). The problem of hypoxia is expected to worsen in the coming years, affecting various aquatic habitats, including estuaries, lakes, ponds, and nearshore coastal areas (Denise et al, 2018;Serghei et al, 2020), leading to signi cant changes in the community composition of aerobic organisms like sh (Duskey et al, 2023).…”