A food chain is a sequence of organisms in which each organism is dependent on the one before it for food. It represents the flow of energy and nutrients through an ecosystem. At the base of many food chains are microscopic plants called diatoms. Diatoms are single-celled algae that are found in freshwater and marine environments.

Diatoms are photosynthetic organisms that use energy from the sun to produce their food. They form the base of many marine food chains because they are eaten by small animals called crustaceans. Crustaceans are a diverse group of animals that includes shrimp, crabs, and lobsters. They feed on diatoms and other microscopic plants and animals in the water.

Herrings are a type of fish that feed on crustaceans and other small animals. They are often found in large schools and are an important food source for many predators, including larger fish, marine mammals, and seabirds.

Therefore, the correct sequence of the given food chain is diatoms-crustaceans-herrings, as diatoms are at the base of the food chain and are consumed by crustaceans, which in turn are eaten by herrings.