Periodic Reporting for period 1 - OxyTempFish (The Metabolic Niche Framework – Linking Metabolic Changes and Behavioural Responses of Fishes to Climate Change.)
Período documentado: 2021-09-01 hasta 2023-08-31
Climate change is driving rising ocean temperatures, increasing the severity and intensity of heatwaves, and expanding areas with low oxygen levels. These changes are already affecting the abundance and distribution of fishes, with more pronounced effects expected in the future. Fish metabolism is constrained by both elevated temperatures and reduced oxygen levels; yet little is known about the role of metabolic changes in shaping the responses of fishes to these environmental stressors. Understanding how climate change affects the abundance and distribution of fishes through changes in their metabolism is important for managing fisheries that support food security and livelihoods, protecting marine biodiversity under the EU Biodiversity Strategy and the Marine Strategy Framework Directive, and forecasting ecosystem changes that will affect coastal communities and economies across Europe. Using zebrafish as a model species, this fellowship aimed to (1) establish a Metabolic Niche Framework to describe how fish metabolism changes in response to concurrent variation in water temperature and oxygen levels, and (2) use this framework to investigate the role of metabolic changes in shaping the thermal tolerance limits of zebrafish and their behavioural responses to changes in temperature and oxygen. The fellowship successfully established the Metabolic Niche Framework, demonstrating that thermal tolerance limits and their hypoxia sensitivity depend critically on acclimation temperature and warming rate, rather than fixed species properties as previously assumed. Furthermore, behavioral responses to progressive hypoxia were shown to correlate with the metabolic traits underlying physiological hypoxia tolerance, revealing a direct link between metabolic changes and behavior.
The fellowship began with the development of essential equipment - most notably a low-cost, optocoupler-based regulation system (OptoReg) that interfaces with widely available FireSting oxygen meters, effectively converting them into oxygen regulators. At approximately EUR 500 for a four-channel unit, compared with more than EUR 10,000 per channel for commercial systems, OptoReg removes a major financial barrier to multi-stressor climate research. Additional equipment included programmable temperature controllers, individual-chamber CTmax arenas, and behavioural arenas with remote monitoring capabilities. Using these systems, experimental work was conducted across three work packages. WP2 quantified the oxygen limit for thermal tolerance (PCTmax) across multiple oxygen levels, warming rates, and acclimation temperatures, revealing that PCTmax is not a fixed species property but depends critically on thermal exposure history and warming rate. WP3 established the Metabolic Niche Framework by combining measurements of standard metabolic rate, critical oxygen tension, incipient lethal oxygen saturation, and accumulated oxygen deficit with thermal tolerance assays, demonstrating that the anaerobic transition line – where aerobic metabolism becomes unsustainable – shifts systematically with acclimation temperature and warming rate. WP4 investigated behavioural-metabolic linkages using a sequential experimental design in which individual fish were first assessed for hypoxia-avoidance behaviour and subsequently transferred to respirometry, revealing that behavioural responses to progressive hypoxia correlate with metabolic traits underlying physiological hypoxia tolerance rather than baseline metabolic rate. During the fellowship, the fellow delivered teaching in four undergraduate courses: Animal Ecophysiology and Ecotoxicology (BI2025), Animal Structure and Function (BI1006), Human Anatomy and Physiology (BI2024), and Special Zoophysiology (BI3021), and served as course organiser for Special Zoophysiology and leader of the annual one-week field course for Animal Ecophysiology and Ecotoxicology. The fellow also served as main supervisor for one Erasmus master's student and co-supervisor for two PhD students. International collaborations were established through participation in two collaborative research expeditions at the Kristineberg Center for Marine Research and Innovation in Sweden. These expeditions brought together researchers from Canada, the United States, Australia, Denmark, Norway, and Sweden, resulting in co-authored publications in Methods in Ecology and Evolution and PLOS Biology, with additional manuscripts currently under review and in development. Research results have been disseminated through (1) first-authored and co-authored peer-reviewed publications in Conservation Physiology, Journal of Thermal Biology, Physiology, Methods in Ecology and Evolution, and PLOS Biology, with additional first-authored manuscripts from the fellowship's core datasets currently in preparation; (2) conference talks and posters at three consecutive Society for Experimental Biology annual meetings; (3) invited symposium presentations at Aarhus University; and (4) departmental seminars at NTNU. Public engagement has been achieved via social media and through research lectures and seminars delivered to students at NTNU. The OptoReg system has been adopted by several international laboratories.
This fellowship advances the state of the art by demonstrating that upper thermal limits, and their sensitivity to aquatic hypoxia, are not fixed species properties but depend critically on acclimation temperature and warming rate. This finding challenges decades of thermal biology methodology and reveals that standard rapid-warming protocols can systematically misestimate hypoxia tolerance under ecologically realistic warming conditions. The Metabolic Niche Framework provides an integrated tool for predicting how combined ocean warming and deoxygenation constrain fish metabolism, while the discovery of direct links between metabolic change and behaviour offers new mechanistic insight into fish responses to water temperature and aquatic hypoxia. Climate modellers can incorporate these mechanistic insights into Species Distribution Models to improve projections of how fish populations will respond to combined warming and deoxygenation under IPCC scenarios. First-authored manuscripts presenting the core experimental datasets are currently in preparation for submission to high-impact journals. Ongoing collaborations established during the fellowship are expected to yield additional co-authored publications addressing multi-stressor climate impacts across diverse species, directly informing European climate adaptation policies and fisheries management strategies while strengthening global research capacity through the widespread adoption of the OptoReg system.