Context: Below is a food web from an ocean ecosystem in Monterey Bay, off the coast of California.
A food web models how the matter eaten by organisms moves through an ecosystem. The arrows in a food web represent how matter moves between organisms in an ecosystem.
Which of the following organisms is the producer in this food web?
A. bat star
B. sea cucumber
C. black rockfish
D. phytoplankton
From the given choices, select the correct answer and reply with the letter of the chosen option.

D