Zombie ideas in marine ecology: ruminations around thresholds for hypoxia impacts

Hypoxia is defined as depression of dissolved oxygen levels below saturation, and can have negative impacts on plants and animals reliant on oxygen for growth and survival. Thresholds for hypoxia in marine pelagic systems have traditionally been defined as 2 mg/l or thereabouts in the academic literature. However, this is well below saturation, and well below the threshold for negative impacts on physiology, growth, and survival for many organisms. In contrast, threshold for hypoxia in freshwater and in most jurisdictional regulations are typically set at much higher values (range of 4-6 mg/l). The origin of thresholds for hypoxia in marine pelagic systems is obscure, but appears to be based on catastrophic collapse or change in community structure, while thresholds in freshwater are based on incipient impacts to individual growth or survival. Dr. Rosenfeld speculates on the origins of this discrepancy and it’s implications for management and perceptions of impact in freshwater and marine ecosystems

The importance of collaborative interdisciplinary research to white sturgeon recovery and conservation

White sturgeon is a species of conservation concern throughout its range, and within British Columbia half of the populations have been undergoing recruitment collapse for over 50 years. Chronic recruitment failure of populations residing in three large, regulated rivers represents an existential threat in the absence of hatchery inputs and habitat remediation. Three areas of interdisciplinary research provide important support for white sturgeon management and recovery. First, interdisciplinary collaboration between the fields of biology and fluvial geomorphology identified the need for spawning habitat remediation. Ongoing research supports the challenges of implementation and monitoring of physical habitat restoration in large rivers. A second interdisciplinary research area arose from the unexplained mortalities of large white sturgeon in the summer of 2022. Evaluation of metal/PCB/dioxin levels in recovered carcasses provides the opportunity to evaluate toxin loads in this long-lived apex predator that may experience both bioaccumulation and biomagnification. Third, eco-physiological investigations of white sturgeon thermal tolerance provide important inputs for evaluating the effects of climate change. Evaluation of multiple life stages has identified thermal thresholds that can support evaluations of thermal risks to wild populations. Interdisciplinary collaborative research on white sturgeon provides an example of effectively linking basic science to applied applications in support of fish conservation in BC.