Going with the Flow: The Forces That Affect Species' Movements in a Changing Climate

García Molinos and his collaborators in the UK and Germany have developed a simple metric to capture the directional agreement between surface ocean currents and warming. They used it in combination with other parameters to build an explanatory model for 270 range shifts in marine biota reported around the globe.

They found that species expanded their range faster and kept track of climate better when ocean currents matched the direction of warming. “We were expecting ocean currents to be most influential at the leading ‘cold’ edge of a species’ range, where warming represents an opportunity for the expansion of its range,” comments García Molinos. “In those situations it’s a little bit like a conveyor belt at an airport terminal. If you want to get to your boarding gate and you walk with the belt, you approach the gate faster than if you just stand on it passively. If you take the belt that goes in the opposite direction you will need to walk fast or even run to make progress.”

However, matching ocean currents and warming unexpectedly slowed down range contractions, or the speed of withdrawal at the “warm” edges. “This was somehow a surprise because we were expecting contraction rates to be mainly driven by the rate of warming,” says co-author Prof. Michael T. Burrows. The authors hypothesized this effect to be related to how currents link local populations within a species’ range.