The next time you’re stuck in traffic, your train runs late, or your bicycle gets a puncture on your way to work, spare a thought for our ocean’s zooplankton, which have the hardest daily commute of all.

Zooplankton, which form a crucial part of the ocean food web, and range from millimetres to just a few centimetres, make daily vertical migrations up to a few hundred metres in the water column. Sheltering in the safety of the deep ocean during the day, these small animals migrate upwards to feed near the surface at night, using the cover of darkness to reduce the risk of being eaten themselves, before once again swimming to the deep. Such vertical migrations through the water column, in response to the changing light, are a mammoth challenge – if you compare body lengths, it’s the equivalent of humans completing two ultra-marathons a day.

But even more fascinating is how zooplankton ‘see’ this underwater light at depth, especially at the poles when they have light all summer and darkness all winter.