As the sun sets, countless zooplankton begin their migration from the bottom of the ocean to the surface. Under cover of darkness to avoid predators, they feed on the phytoplankton that thrive in the sunlit waters, returning to deeper waters as the sun rises once more. Called "diel migration", this phenomenon is known as the greatest animal migration on Earth. This vertical movement en masse influences many processes, such as the flux of organic matter from the surface to deeper waters.

While many species of zooplankton can actively adjust their mobility, turbulence can still have an impact.

"Turbulence has been suggested to have significant effects on survival strategies of zooplankton, by modulating their feeding efficiency and predator detection," explains Dr Mamoru Tanaka, a post-doc with the Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST). What's more, Tanaka notes, turbulence is also thought to influence zooplankton's diel migration patterns.

With field observations scarce, Tanaka and colleagues sought to study the relationship between turbulence and diel migration in the real world at two sites with entirely different types of habitat.

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