epipelagic

The epipelagic zone, also known as the sunlight zone, is the uppermost layer of the ocean, extending from the sea surface down to about 200 meters (660 feet). It encompasses most of the photosynthetically active region of the ocean and receives the majority of the sun’s energy, making it the area with the highest overall productivity.

Light and temperature dominate the epipelagic environment. Sunlight enables photosynthesis by phytoplankton, forming the base of pelagic food webs. Temperature and light availability vary with latitude and season, and surface mixing by winds and currents influences nutrient distribution. In some regions, upwelling brings nutrients into the zone, supporting intense biological activity near coasts.

Ecology within the epipelagic is dominated by planktonic communities and a diverse array of nekton. Phytoplankton and microzooplankton support zooplankton populations, which in turn feed small fish, squid, and larger predators such as tuna, mackerel, sharks, and billfish. Many species undertake diel vertical migrations, feeding higher in the water column at night and descending during the day to avoid predators, thereby linking surface productivity with deeper waters.

The epipelagic is ecologically and economically important. It supports major fisheries that harvest forage fish and large predators, and it plays a central role in the marine carbon cycle through rapid turnover of organic matter. The zone varies with geography, experiencing high productivity in upwelling regions and lower productivity in subtropical gyres.