Answer: Plankton
Step-by-step explanation:
Plankton are small organisms that exist in water and are too weak to swim against the currents of the ocean and the seas. This leads to them going wherever the currents take them. Plankton can be either plants or animals.
Of the organisms listed, they are on the lowest trophic level and provide a source of food to other organisms of different sizes ranging from krill to whales.