Climate change impacts vary with depth: what can be the consequences for pelagic ecosystems and for conservation ? Examples from the Southern Indian Ocean.

Climate change is a threat to the rich biodiversity in the Southern Indian Ocean (20 -120°E, 70-30°S) but studying climate change impacts remain a challenge, notably for pelagic ecosystems that evolve in a 3D environment. We illustrate this issue with two studies in the Southern Indian Ocean:  i) the comparison of the speed of isotherm drift (i.e. climate velocity) between the surface and at depth in global climate models, and ii) the study of marine heatwaves and climate change impacts on a subsurface water mass playing an important role for marine top predators foraging behavior. These examples highlight the need to account for depth when assessing species vulnerability to climate change and potential options for climate-adapted efficient conservation are raised.