Animals and plants must survive by eating; plants use energy from water, sun, and carbon dioxide to make their food. They are called producers since they make their own food. Consumers are organisms which feed on either animals or plant as they cannot create their own food. Marine food chain is composed of energy producers and consumers where phytoplankton are the base of the sea. There is a chain that food passes, phytoplankton are eaten by zooplankton making them the primary consumers.
In this case, Phytoplankton -------> zooplankton ------- herring--------------salmon
Zooplankton is the primary consumer
Fenchel, T. (2003, November 28). (PDF) Marine plankton food chains. ResearchGate. https://www.researchgate.net/publication/234150539_Marine_Plankton_Food_Chains