Final answer:
Zooplankton, crabs, and krill belong to the tropic category of Herbivore in the food chain.
Step-by-step explanation:
In the food chain, zooplankton, crabs, and krill belong to the tropic category of Herbivore. Herbivores are organisms that consume plants or phytoplankton, which are the primary producers in the food chain. Zooplankton, crabs, and krill feed on phytoplankton, making them herbivores.