Shrimp are primary consumers that feed on photosynthetic organisms. why would these organisms likely be found only in shallow ocean zones?

Since shrimp pray on photosynthetic organisms, they are dependant on their prey's location.
The photosynthetic organisms need sunlight in order to produce energy, so they then to live in shallow waters, because the sunlight penetrates only a small upper layer of the water's surface.
So, shrimp live in shallow waters because their pray can only live there.

The amount of light in deeper ocean zones is too dim for photosynthesis.