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Ocean wave crashing

There are two major aquatic or water biomes, the marine biome and the freshwater biome. The marine biome is primarily made up of the saltwater oceans. It is the largest biome on planet Earth and covers around 70% of the Earth's surface. Go here to learn more about the world's different oceans.

Types of Marine Biomes

Although the marine biome is primarily made up of the oceans, it can be divided up into three types:
  • Oceans - These are the five major oceans that cover the world including the Atlantic, Pacific, Indian, Arctic, and Southern Oceans.
  • Coral reefs - Coral reefs are small in size when compared to the oceans, but around 25% of marine species live in the coral reefs making them an important biome. Go here to learn more about the coral reef biome.
  • Estuaries - Estuaries are areas where rivers and streams flow into the ocean. This area where freshwater and saltwater meets, creates an ecosystem or biome all its own with interesting and diverse plant and animal life.
Ocean Light Zones

The ocean can be divided up into three layers or zones. These layers are called light zones because they are based on how much sunlight each area receives.
  • Sunlit or euphotic zone - This is the top layer of the ocean and it gets the most sunlight. The depth varies, but averages around 600 feet deep. The sunlight provides energy to the ocean organisms through photosynthesis. It feeds plants as well as small little organisms called plankton. Plankton are very important in the ocean because they provide the food basis for much of the rest of ocean life. As a result, around 90% of ocean life lives in the sunlit zone.
  • Twilight or disphotic zone - The twilight zone is the middle zone in the ocean. It runs from about 600 feet deep to around 3,000 feet deep depending on how murky the water is. There is too little sunlight for plants to live here. Animals that live here have adapted to living with little light. Some of these animals can produce their own light through a chemical reaction called bioluminescence.
  • Midnight or aphotic zone - Below 3,000 or so is the midnight zone. There is no light here, it is completely dark. The water pressure is extremely high and it is very cold. Only a few animals have adapted to live in these extreme conditions. They live off of bacteria that get their energy from cracks in the Earth at the bottom of the ocean. Around 90% of the ocean is in this zone.
Animals of the Marine Biome

The marine biome has the most biodiversity of all the biomes. Many of the animals, such as fish, have gills that allow them to breathe the water. Other animals are mammals that need to come to surface to breathe, but spend much of their lives in the water. Another type of marine animal is the mollusk which has a soft body and no backbone.

Here are just a few of the animals that you will find in the marine biome:
  • Fish - Sharks, swordfish, tuna, clown fish, grouper, stingray, flatfish, eels, rockfish, seahorse, sunfish mola, and gars.
  • Marine mammals - Blue whales, seals, walruses, dolphins, manatees, and otters.
  • Mollusks - Octopus, cuttlefish, clams, conch, squids, oysters, slugs, and snails.
Great white shark in ocean
Great White Shark

Plants of the Marine Biome

There are thousands of species of plants that live in the ocean. They rely on photosynthesis from the sun for energy. Plants in the ocean are extremely important to all life on planet earth. Algae in the ocean absorbs carbon dioxide and provides much of the Earth's oxygen. Examples of algae include kelp and phytoplankton. Other ocean plants are seaweeds, sea grasses, and mangroves.

Facts About the Marine Biome
  • Over 90% of the life on Earth lives in the ocean.
  • The average depth of the ocean is 12,400 feet.
  • Around 90% of all volcanic activity takes place in the world's oceans.
  • The Mariana Trench is the deepest point in the ocean at 36,000 feet deep.
  • The largest animal on Earth, the blue whale, lives in the ocean.
  • Humans get most of their protein by eating fish from the ocean.
  • The average temperature of the ocean is around 39 degrees F.
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