Why are copepods and krill important in ocean food chains?

Copepods and krill are essential components of marine food chains because they serve as vital, high-energy food sources for a wide array of larger marine life.123

• Copepods: As key holoplankton, these small crustaceans are widely distributed throughout the world's oceans. They act as a primary link in the food web, providing direct or indirect nutrition for most commercially important fish species. Some species are omnivorous, consuming both phytoplankton and other zooplankton, which allows them to transfer energy efficiently through different trophic levels.12
• Krill: These shrimplike euphausiids are critical to the health of marine ecosystems, particularly in Antarctic waters. They exist in vast swarms and serve as the primary prey for numerous whales, birds, and fish. Because they are highly nutritious, their abundance directly supports the survival of large predators, including blue whales and penguins.34

Both groups are fundamental to the biosphere, as their grazing activities help regulate phytoplankton populations, and their role as prey sustains the biodiversity of the global ocean.23