Microscopic Migration
Zooplankton, the microscopic plankton consisting of small animals and the immature stages of larger animals, move up and down the water column in a type of migration called diel vertical migration. Whether they reside in the ocean or freshwater habitats, these plankton travel to safer depths in the morning and rise closer to the water’s surface as the sun sets.
The purpose of this unusual daily routine? Zooplankton’s favorite snacks live closer to the water’s surface. Unfortunately, this is also the most dangerous place for zooplankton—the closer they are to sunlight, the more visible they are to predators. In order to eat without being eaten, they must travel upward after dark. It’s a delicate dance between preying on their next meal on the ocean’s surface and avoiding becoming someone’s next meal while they’re there.
In case you’re curious about the appearance of these miniscule organisms, the images below are examples of the many types of zooplankton inhabiting our blue planet:
Amphipods are shrimp-like crustaceans that reside both in marine and freshwater habitats.
Image via Wikimedia Commons
Copepods are a type of crustacean that provides food for many species of fish.
Image via Wikimedia Commons
Antarctic krill is a keystone species of the Southern Ocean ecosystem, serving as the main prey for fish, penguins, seals and whales.
Image via Wikimedia Commons
Northern krill lives in the North Atlantic Ocean and is preyed on by whales, fish and birds.
Image via Wikimedia Commons
Tomopteris is a genus of marine planktonic polychaete that spends its entire life cycle in the water column.
Image via Wikimedia Commons
Eel larvae drift along the Gulf Stream with other zooplankton.
Image via Wikimedia Commons
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