With over 70 percent of the Earth covered in water, oceans, bays and tributaries make up the largest biome – or ecosystem – on the planet. Scientists have found over 1 million species of animals and plants living here and they believe there may be as many as 9 million species yet undiscovered.
- The ocean is divided into three zones – the euphotic zone, the disphotic zone and the aphotic zone.
- The euphotic zone is closest to the water’s surface. Here, sunlight warms the water. Phytoplankton and algae convert the sun’s light to food. Zooplankton eat the phytoplankton. Fish eat the zooplankton and larger fish and water mammals eat the fish. Most of the animals in the sea live in this zone.
- The disphotic zone is sometimes called the twilight zone because its light resembles twilight on land. The aphotic zone is very dark and very cold. Although this zone is the largest habitat on Earth, few oceanic animals can live here.
- Algae and phytoplankton take in carbon dioxide and produce more oxygen than any other organism on Earth. Without them, we probably could not survive.
- Shallow seafloors near the coasts support a wide variety of oceanic life. Bottom-feeding fish, such as cod live here, as well as mollusks, anemones, sea urchins, crustaceans and starfish. They feed on plankton and other fish.
- Some deep-ocean creatures glow in the dark. This is called bioluminescence. The glow can help them attract a mate, confuse a predator or even find food.
- Sperm whales dive into the twilight zone in search of food, such as giant squids. These mammals are specially equipped to dive to great depths and can remain underwater for up to 90 minutes.
- Euphotic zone: area closest to the ocean’s surface
- Disphotic zone: known as the twilight zone, this area of the ocean is colder and darker than the euphotic zone.
- Aphotic zone: the deep ocean – completely dark and very cold
Visit the University of California Santa Barbara to learn more about the marine world.
Question: Are all oceans salty?
Answer: In general, yes. Dissolved salt runs from lakes and rivers into the ocean where it becomes concentrated. One gallon of ocean water usually contains about one cup of salt. The Dead Sea is so salty that nothing can live there. Salt makes the water heavier so things float more easily. Many fish and marine animals have soft or non-existent skeletons. The water supports them instead. Jellyfish, for example, float easily in the water, but they can’t survive on land.