They have no use for it, just like they dont have any type of respiratory organs like lungs.
Explanation:
In the case of nutrition and digestion they obtain food by capturing their prey with their pseudopodia. The food is internalized through a type of endocytosis known as phagocytosis. Nutrients are obtained as the enzymes digest the food inside the vacuole and when they are finished the food vacuole dissolves.
I believe the correct answer is upwelling. Lets say we have producers such as plankton. well upwelling currents bring dead matter from the ocean floor up to the surface, creating plankton.
