The denizens of the deep ocean may seem as strange as aliens from another planet but these creatures are products of the same biochemistry that impels other animals. Driven by the need for food and to avoid predators, deep-sea marine animals – especially tiny free-floating zooplanktons – swim up to the surface at night. This synchronised movement is called diel vertical migration (DVM), and it makes for a captivating display of nature’s ingenuity. It is also a crucial player in the earth’s carbon cycle.
At DVM’s heart lies a delicate balance between the need to feed and to avoid becoming prey. Zooplankton in particular are constantly wary: they can stay in dangerous waters during the day, looking for food, or swim down to the twilight zone and risk starvation. DVM is a way to cut past these terrible options and live the best of both worlds.
As the sun dips below the horizon, deep-sea organisms rise from the mesopelagic layer (200-1,000 m deep) to the epipelagic layer, where darkness provides a cloak of safety. This nightly ascent allows them to graze on the microscopic phytoplankton while skirting the haunts of their daytime predators. The timing of this migration is tuned to the natural rhythms of sunrise and sunset, and the migration itself is the largest on the planet by biomass. And it occurs daily in all oceans.
