Answer:
-Phytoplankton.
Step-by-step explanation:
Producers in an ecosystem are autotrophic organisms that can synthesize food by their own. Phytoplanktons are autotrophic, microscopic marine organisms, considered as the main producers in the ocean ecosystem.
They include photosynthetic algae and bacteria, which use sunlight as source of energy and convert it into chemical energy (as food) for consumers.
Thus, the correct answer is option). phytoplankton.'