The correct option is A Phytoplankton
Phytoplanktons are the major producers and constitute the base of five level food web of the marine ecosystem. They convert chemical energy into the usable form of energy. Zooplanktons and other herbivores feed on phytoplanktons and these herbivores are themselves eaten by higher level consumers. Fishes and whales occupy higher level as consumers. Kelps occupy the base of the food web in kelp beds only. The correct answer is option A.