These sperm whales are about to dive from clear blue waters to depths of 1000m in search of food.
Their journey takes them from the warm sunlight layer, through the twilight zone and into total darkness.
As they reach 200m, sunlight begins to fade.
They have entered the mesopelagic zone or twilight zone.
Mesopelagic zone: Depth:
200m to 1000m
Temperature: 4°C to 5°C
It's too dark here for photosynthesis to occur, so plants do not grow, meaning animals are scarcer than in the zones above.
Most animals are transparent, like the giant amphipod, to conceal themselves within the dark.
Predators have evolved to have huge eyes, to seek out prey in the twilight.
As the whales reach 1000m, they enter total darkness, and their lungs are crushed to 1% of their normal size.
This is the bathypelagic zone, or midnight zone.
Bathypelagic zone: Depth:
1000m –to 4000m
Temperature: 0°C to 2°C
This dark world contains alien creatures.
Most creatures have soft bodies so they are not damaged by pressure, and are either red or black to blend into the darkness, like the vampire squid.
Others use bioluminescence to create their own light, to attract prey, find a mate, or as defence.
Emission of visible light by living organisms
Pigments react with oxygen to create light
The deep sea angler employs a glowing fishing rod to entice prey, while the periphylla jelly uses a light display to frighten predators.
Every night, millions of animals migrate from the deep to feed, forming one of the largest migrations on Earth.
At dawn, they return to the depths of the bathypelagic zone, but the ocean gets far deeper and darker than this.