Climate-change-driven cooling can kill marine megafauna at their distributional limits

The impacts on marine species from secular warming and heatwaves are well demonstrated, however the impacts of extreme cold events are poorly understood. Here, we link the death of organisms from 81 species to an intense cold upwelling event in the Agulhas Current, and show trends of increasing frequency and intensification of upwelling in the Agulhas Current and East Australian Current. Using electronic tagging, we illustrate potential impacts of upwelling events on the movement behaviour of bull sharks, Carcharhinus leucas including alterations of migratory patterns and maintenance of shallower dive profiles when transiting through upwelling cells. Increasing upwelling could result in “bait-and-switch” situations, where climate change expands subtropical species’ distribution, while simultaneously exposing climate-migrants to increased risk of cold-stun/mortality events at poleward distributional limits. This shows the potential impacts of increased cold events, an understudied aspect of climate-change research, and highlights the complexities of climate change effects on marine ecosystems.