Where does most of the primary production occur in an ocean ecosystem?

It mostly occurs in the marine plants and photosynthetic organisms of the ocean and seas. These organisms similar to the land plants process the sunlight and CO2, with water to produce glucose which serves as the food for itself. Along with the producer, it will serve as the food for the heterotroph of the sea. 

The answer to that question is a

Hold on to his or her beliefs even if there is no evidence for those beliefs.