Final answer:
Plankton are mainly found in the photic layer of the pelagic zone, which covers areas where sunlight can penetrate, like the neritic and part of the oceanic zones, facilitating photosynthesis.
Step-by-step explanation:
The majority of plankton would be found in the pelagic zone, which encompasses both the neritic and oceanic zones of the ocean. Plankton are primarily located in the photic layer of the pelagic zone where sunlight penetrates the water, allowing photosynthesis to occur.
Therefore, the photic zone which includes regions such as the intertidal zone, the neritic zone, and part of the oceanic zone is where the most photosynthetic activity and plankton would be found.