What is plankton & why do plankton help support a thriving fish population?

Plankton are mostly drifting microscopic life in water. Many forms of plankton like Diatoms are important contributors to oxygen levels in the ocean as well as an important part of the food web that support larger animals higher up on the food web

It's lithogenous i believe of course i looked it up.

Here is a picture  of the net. its 4 squares in a row diagonal and on the third draw one square aove and under