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.