The top layer in the ocean, extending from the ocean's surface to a depth of 200 metres (656 feet). This zone is the only place in the ocean where there is enough light to permit photosynthesis. The boundary between the epipelagic zone and the mesopelagic zone is where the level of dissolved oxygen begins to decrease significantly. This is due to the lack of primary production and because of the sinking of rotting dead organic material.

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