Regional downscaling of eco-physiological theory. Confronting global predictions with local observations.

In the face of current and future global warming, we need predictive models that forecast ecological consequences. For marine systems, such models typically consist of a global climate projection model coupled to various temperature-dependent functions that represent biological and physiological responses. Most of these functions are highly generalised and based on averages across many species and systems. Likely, such models will be wrong when applied to specific species or in particular regions. However, we don’t know, because they are almost exclusively used to predict the future, and rarely the past. In this proposal, we pick key expectations from these global predictive models and downscale them to regional conditions for key Norwegian fish stocks using particularly long and detailed timeseries of biological data, experiments and mechanistic models of bioenergetics and life histories. Preliminary analyses suggest that several fish species have more physiological and behavioural flexibility than generalised models give them credit for. These and future project outcomes will contribute to making better predictions, but hopefully also broaden our understanding of how temperature work and don’t work on different biological processes.

In the face of global warming, state-of-the-art eco-physiological theories and their implementation in global models make sweeping predictions that high-latitude fish populations are imperilled from unavoidable physical-physiological mechanisms. These are often rooted in reproductive constraints, and at the base we find two main theories: 1) The theory of thermal tolerance windows, predicting that spawning fish (with narrow tolerance) will encounter unavoidable thermal bottlenecks in a warming ocean. 2) The theory of temperature-dependent physiological rates, predicting an unfavourable advancement of fish spawning time, causing offspring to fall out of sync with their zooplankton food – known as trophic asynchrony These are predictions, often drawn from controlled laboratory experiments, and in turn extrapolated to global models. But just as downscaling to regional specificities and higher resolution was necessary to improve predictive ability of earth system models, so a similar biological downscaling to particular ecosystems and species is required to assess predictions at the scale relevant for population processes and ecosystem dymanics. In this project we will downscale these predictive theories for two test species - Atlantic cod and herring, among the best documented fish stocks in the world. Our previous publications and preliminary findings suggest that these species have remarkable plasticity in the timing of spawning, often opposite to that dictated by temperature, and in surprising synchrony with each other and with lower trophic levels. Here, we pick key expectations from the high-profile literature on biological effects of ocean change and attempt to downscale these to local conditions for key high-latitude fish species using particularly long and detailed timeseries of biological data, remote sensing, high-resolution water column processes, individual behavioural observations, and biological models of bioenergetics and life histories.