Zooplankton are bite-sized, energy-rich snacks for many predators, such as fish, whales, and seabirds. These predators are fast and use their eyes to detect their food, which means that they are most effective at hunting during the day and in the sunlit surface water. However, the zooplankton's food source, tiny plants known as phytoplankton, are also only found in the surface water.
So, the zooplankton face a dilemma: if they stay in the surface waters to feed, they risk being eaten. If they hide in the deep, they will be safer, but soon starve. This is what we call a tradeoff: each option (to feed or to hide) brings with it a gain, but also a cost. DVM is the zooplankton's clever solution to balance this tradeoff and have the best of both.
Much like a game of hide-and-seek, the zooplankton remain in the deep, dark waters during daylight hours, out of sight of their predators. Under the cover of nightfall, they migrate upwards from the mesopelagic layer to the epipelagic layer, where they can graze in the relative safety of darkness at night.

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