Deep-Sea Creatures
Explore life in the deep sea: animals that make their own light (bioluminescence), creatures adapted to crushing pressure and total darkness, and hydrothermal vents where life thrives without sunlight
What a learner can do afterwards
- Define bioluminescence as the ability of some deep-sea creatures to produce their own light
- Describe at least two adaptations deep-sea animals have for life in darkness and pressure
- Explain that hydrothermal vents support life without sunlight through chemical energy
1 · Read
You already know that sunlight fades out as you go deeper into the ocean, until it is pitch black. Down there, the water also presses down with crushing force. So how does anything survive? Many deep-sea animals make their own light. This is called bioluminescence, a chemical reaction inside their bodies that glows like a built-in flashlight.
The anglerfish dangles a glowing lure right above its mouth. Smaller fish swim toward the light, curious about what it could be. The moment they get close, the anglerfish snaps them up. Its own light becomes a trap.
Darkness and pressure both call for special bodies. Many deep-sea animals have huge eyes that catch even the faintest glow. Their bodies are also soft and flexible, with no big air pockets, so the crushing pressure cannot harm them.
Some parts of the deep sea have hydrothermal vents, cracks in the ocean floor that spray out hot water full of chemicals. No sunlight reaches down there, but tiny bacteria use those chemicals to make food energy. Tube worms, crabs, and other animals feed on the bacteria, so a whole community thrives without any sunlight at all.
Deep-sea animals survive total darkness and crushing pressure with glowing light, huge eyes, and flexible bodies, and near hydrothermal vents, life runs on chemical energy instead of sunlight.
The rewritten readings were written for this dataset.
More to read
Life at different ocean depths
Ocean zones change as you travel down through the water. Near the surface, the sunlight zone has enough light for plants to grow. Much ocean life depends on this sunlit water.
In the twilight zone, the remaining light is faint and blue. Farther down, the midnight zone receives no sunlight. Pressure there is enormous and can crush an air-filled object such as a car. Some animals, including deep-sea anglerfish, use glowing light to attract prey.
Below lies the abyssal zone, followed by the hadal zone in deep trenches. Animals survive even in these cold, dark waters under great pressure.
Some communities live near hydrothermal vents, openings that release hot water from the seabed. Bacteria there obtain energy from chemicals and make food without sunlight. They support other living things around the vents.
Ways animals survive in deep water
Deep-sea animals have features that help them live in darkness. Some anglerfish inhabit water near the seabed, while others swim above it. A female deep-sea anglerfish carries a stalk with a glowing end above her head. Smaller animals approach this lure, and she catches them. Bacteria living in the lure produce its light.
Light produced by living things is called bioluminescence. Deep-sea creatures use it to catch prey, conceal themselves or attract mates. Large eyes can collect faint light. Many deep-water animals also have soft bodies suited to life under high pressure. Features that look frightening to us can help these creatures survive without sunlight.
Names for ocean habitats
Scientists name ocean habitats to describe where animals live. In the aphotic zone, sunlight is too weak for photosynthesis, the process plants use to make food. Its deepest waters receive no sunlight.
The abyssal zone lies about 4,000 to 6,000 metres deep. At 4,000 metres, the water is roughly as deep as nine Empire State Buildings stacked upright. Trenches reach farther down.
The benthic zone means the seabed, from the coast to the deepest ocean floor. Deep aphotic and abyssal waters are dark, close to freezing and under very high pressure.
Food and possible beginnings at vents
Life may have begun near hot springs or hydrothermal vents billions of years ago. Scientists are still studying this possibility.
A hydrothermal vent releases heated water containing minerals through an opening in the seabed. Deep-ocean vents receive no sunlight, so plants cannot grow there. Some prokaryotes, a group that includes bacteria, obtain energy from chemicals in the vent water. They use that energy to make food through chemosynthesis.
Larger animals depend on these tiny organisms for food. This supports communities that live in darkness. Such places may resemble habitats occupied by Earth's earliest life.
Explore more
2 · Watch
به انگلیسیTake it off screen
Where it sits
Learn first
Optional connections
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.