The answer is; 1
Most of the photosynthetic organisms are located in the epipelagic zone of the oceans where sunlight can penetrate before diffusing and becoming too weak to support photosynthesis. The epipelagic zone is filled with plankton. When this plantkon die, they begin to sink slowly to the bottom of the ocean. These plankton are food for small fish. These small fish are food for bigger fishes. This is how an ecosystem is sustained in the deep dark oceans.