ECOSYSTEMS > OPEN SEA
Technically, this is known as the Epipelagic or Euphotic Zone, but Sunlit Zone is easier to remember and much more descriptive. Sunlight can penetrate the water up to approximately 656 feet (200 m), and with the light comes energy, warmth and growth. As a result, this is the open sea zone where most life exists.
Blue whales, the largest animals to ever live, cruise slowly through the Sunlit Zone, eating as much as 8,000 lbs (3,628 kg) of tiny krill per day. This is also where most fish live, hunted by pods of dolphins, soaring seabirds, and yes... bigger fish. Human beings use the Sunlit Zone extensively for both harvesting the ocean's bounty, recreation, exploration and for other natural resources.
As you progress downward through the Sunlit Zone, colors start to fade. The water darkens to a deep blue and many of the lifeforms appear drab. As the visible light diminishes, so does our ability to perceive color. Once you pass into virtual darkness, you’re out of the Sunlit Zone and into the Twilight Zone.