Question

In marine food chains, the ____________ are microscopic organisms called plankton.

Answer 1

They are heteratrophs

Step-by-step explanation:

Plankton are organisms that float with the ocean currents. Plankton can be found in all of the world's oceans, lakes, and rivers. ... Zooplankton are heterotrophs that get their energy from feeding on phytoplankton, bacteria, other zooplankton, or even non-living material in the ocean.

Answer 2

producers, because they produce oxygen