Ocean Habitats Background Information for Teachers, Parents and Caregivers

This page provides information to support educators and families in teaching K-3 students about ocean habitats. It is designed to complement the Ocean Habitats topic page on BrainPOP Jr.

The ocean is home to a startling array of living things. This movie will introduce and explore the three main zones of the ocean: the sunlit zone, the twilight zone, and the midnight zone. It will explore different marine plants and animals like coral, phytoplankton, krill, fish, eels, mollusks, dolphins, and whales. It will explore different ocean habitats and investigate some adaptations of living things that help them survive in their habitats. The movie will also explore how oil spills and other forms of pollution can change ocean habitats, and share ways people can help protect our environment.

About 70% of Earth is covered in water. More than 97% of this water is saltwater found in our oceans and seas. Scientists divide the ocean into different zones according to how much sunlight is received. Living things in each zone have different ways to survive in their habitats. Review with children that a habitat is a place where plants and animals live.

The sunlit zone is the top part of the ocean, and the area that receives the most sunlight. This zone goes from the surface to about 600 feet (roughly 200 meters) underwater. Help children understand that even though the sunlit zone is the smallest zone in the ocean, it actually supports about 90% of all marine life. Here enough light goes through the water to allow plants to grow, and for photosynthesis to take place. We recommend researching online or at the library to find different examples of ocean vegetation. How can plants grow in saltwater? How do they survive in their environment? In the sunlit zone, algae, plants, and phytoplankton thrive and are the basis of nearly all ocean food chains. Remind children that phytoplankton are tiny living things that can use the light’s energy to make their own food, much like plants. Krill, fish, and other animals feed on the phytoplankton, and larger animals feed on the krill. Energy is transferred up the food chain to even larger animals such as dolphins and whales. We recommend screening the Food Chain movie for review.

Coral reefs are also found in the sunlit zone. Remind children that coral is an animal that grows a very hard skeleton. Coral can come together to form reefs that are home to many living things, such as fish, eels, and mollusks. Nutrient-rich plants grow within coral reefs, including seaweed, various algae, and seagrass (which is the only flowering plant in the water). Many people call coral reefs the “rainforests of the ocean.”

The twilight zone is below the sunlit zone, extending from 600 feet to about 3,300 feet (roughly 200 meters to 1,000 meters). Less sunlight is able to penetrate the twilight zone. Many animals migrate between the twilight and sunlit zone in search of food, including the sperm whale and swordfish. Other twilight zone animals include crabs and other crustaceans, dragon fish, viperfish, and many worms. Help children understand that as you get further and further away from the ocean’s surface, less light is filtered through the water. As a result, the water gets colder and colder.

The midnight zone is below the twilight zone, extending from about 3,300 feet (1,000 meters) downward. The depth of the ocean averages around 13,000 feet (4,000 meters). Here no light can penetrate and waters can reach close to freezing temperatures. However, the midnight zone is still able to support creatures that have specially adapted to their environment, and scientists are constantly discovering new forms of marine life even in the deepest part of the ocean. Food can be difficult to find, but bits of dead animals and nutrients can ‘rain’ into the midnight zone and provide food. Some fish, like the fangtooth and the umbrellamouth gulper, have large mouths so they can grab and eat anything that comes their way. Most animals in the midnight zone are blind or have very large eyes to allow light to pass through. Many animals in this zone are also bioluminescent, which means they can emit light through special biological processes. They can glow to attract mates or prey, or to scare off predators. Remind children that the ocean floor is a dark and rocky place. The ocean floor has mountains, trenches, and flat areas just like land. In some places there are vents in the Earth’s crust that give off heat and chemicals. Bacteria feed on the chemicals and other animals use the bacteria for food. Thus, hydrothermal vents can provide an ecosystem for different living things, such as tubeworms and deep-sea clams and mussels. This means the deep sea can support an entire food chain that does not start with the Sun’s energy.

Even as the U.S. Census Bureau counts the American population, marine scientists are conducting a census of their own—of every living thing in the ocean. More than 2,000 biologists from over 80 nations working with the international Census of Marine Life are nearing the completion of a 10-year project. This project has discovered more than 5,000 new forms of marine life, encompassing 16,000 species of sea worms, hundreds of tiny crustaceans and—most numerous of all—microbes. Scientists now estimate that the seas may contain a billion different kinds of microbes. The number of marine microbes may total nonillion—a number represented by 1 followed by 30 zeroes. Microbes may constitute 90% of the seas’ biomass. Large, whitish mats of multicellular microbes can be found on the seafloor throughout the world and one such mat of bacteria, off the coast of Chile, is about the size of Greece. Scientists say they were astonished by the diversity and sheer amount of life in the seas, even at depths once considered too dark, cold, and hostile to support life at all. According to some scientists, the deep sea rivals highly diverse ecosystems such as tropical rainforests and coral reefs.

Review with children that most of Earth is covered by oceans and seas, but they are changing due to human involvement. In many parts of the world, overfishing is a big problem. This is causing certain kinds of fish and other animals to become endangered. For example, in the northeastern part of the Atlantic Ocean, herring and capeling were overfished. This led to decline of the numbers of Arctic cod and also of seabirds, which both relied on these fish for food. Shark, blue fin tuna, and Atlantic salmon are also currently suffering from low stock due to overfishing. Review with children that when something is endangered, very few of its species is left in the wild. Endangered fish can affect food chains and impact life throughout the ocean. You may want to screen the Extinct and Endangered Species movie for review or extension.

Oil spills and other forms of pollution can cause problems for many living things and affect ocean food chains. Oil spills cover marine plants and animals with a film of oil which prevents them from obtaining oxygen or regulating body temperatures. Garbage in our communities can sometimes end up in the oceans through sewers that drain to bays. Illegal ocean dumping is a huge source of pollution in our oceans and seas. Today there are several “islands” of garbage; one such example in the Pacific Ocean is larger than the state of Texas. Remind children to recycle whenever possible and throw their trash into the proper receptacles. Just a simple act can help protect the environment and promote a healthy ocean habitat.

Discuss different ways you can help protect the environment. Encourage children to write to government leaders to make their voices heard about the changing planet. You may want to watch the Sending a Letter or E-mail movies for review. Another simple way children can help protect the environment is to educate one another. They can discuss issues with different people and share what they have learned about pollution and the environment. Encourage children to be good global citizens!