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 these organisms contains matter that was once part of the phytoplankton?
A. black rockfish
B. sea otter
From the given choices, choose the correct answer and respond with the letter of that choice.

A