What is the ocean zone between about 200 and 1,000 meters deep, also called the twilight zone?

The ocean zone between about 200 and 1,000 meters deep, also called the twilight zone, is the mesopelagic zone.

“Mesopelagic” means “middle pelagic.” It lies below the sunlit epipelagic zone and above the completely dark bathypelagic zone. Its upper and lower boundaries are approximate because sunlight fades gradually and vary with water clarity, latitude, and season.

Although faint sunlight penetrates the zone, it is generally too weak for ordinary photosynthesis. Many animals therefore use bioluminescence, camouflage, or large eyes to find food and avoid predators. Some species, including lanternfish, migrate toward the surface at night and return to deeper water by day.

A common mix-up is confusing the mesopelagic zone with the bathypelagic zone. The bathypelagic, often called the midnight zone, begins at roughly 1,000 meters and is essentially lightless. The mesopelagic is also scientifically important because sinking organic matter and migrating animals help move carbon and nutrients through the ocean.