Marine Biology - Life Forms and Habitats in the World's Oceans

Marine biology is the study of the ocean’s plant and animal life. Marine life gives us food, medicine and other raw materials we need. It also maintains tourism and provides us with an area of recreation. Organisms in the ocean produce oxygen and help regulate the earth’s climate. Coasts are partly created by marine life; some marine organisms even help to create new land.

Marine biology ranges from very small organisms, like plankton, to huge 30 meter long whales. Habitats stretch from the ocean’s surface to the ocean trenches which are over 10,000 meters deep.

About 71% of the Earth’s surface consists of oceans. They are, on average, about 4,000 meters deep. A large part of the Earth’s life lives in them, even though not all forms of marine life have yet been discovered.

Studying marine life is a large field of science. The oceans are home to many different species, including fish, birds, reptiles and other organisms. Scientists also research out how organisms live in salt water.


Marine animals and plants


Many birds have adapted to life in ocean regions. Seabirds usually live longer and have fewer young ones than other birds do. Most of them travel thousands of miles a year and cross the equator from the northern to the southern hemisphere. Humans have depended on seabirds throughout history. They have shown seafarers the way and guided sailors to land. Among the best-known are albatrosses and Arctic terns.

Fish belong to the main species that live in the oceans. They range from tiny sardines to dangerous sharks. Fish serve as one of the main sources of food for humans.

Invertebrates are animals that do not have backbones. Many of them live in the sea and around coastal regions, like jellyfish, sea worms, shellfish or octopuses.

The largest mammals of the oceans are whales. Dolphins and sea lions are among other mammals that live in the sea. Sometimes the polar bear is referred to as a sea animal because it depends on seafood.

Most marine reptiles live in or near the coastal waters. They include sea turtles and saltwater crocodiles. Many species need to come to land to lay their eggs.

There is a very diverse plant life in the world’s oceans. Algae and sea grass are among the most common. Such plants have become used to a salty environment. Different types of plants also grow in areas where the water surface is affected by the rise and fall of the tides.



Different forms of life live in various areas of the ocean. Some are limited to the coastal and shelf areas, while others live in the open sea.



Coral reefs are found in the tropical areas of the world, but they can also exist in colder water. Reefs are built by corals and other animals that deposit calcium on rocks. They are home to a vast variety of different life forms. About half of the world’s coral reefs, however, are in danger because of global warming and a rise in sea temperatures.

Although we do not know very much about what kind of life forms exist in deep water trenches, marine scientists have found out that a certain type of jellyfish and a flatfish were seen in the Mariana Trench, the world’s deepest ocean area. Generally these parts of the ocean have little or no sunlight and many organisms that live here have to produce their own light.

Marine biologists also study how waves, currents and the tides affect organisms living in the world’s oceans. Little is known about where certain species travel to breed.


Related Topics


  • adapt to = get used to
  • affect = to have an effect on
  • algae = simple plant without stems or leaves that grows in or near the water
  • although = while
  • breed = to get together in order to have babies
  • calcium = silver white metal that helps form teeth and bones
  • coastal = where sea and land meet
  • current = a steady movement of water in a lake, sea or ocean
  • depend on = need
  • deposit = set down
  • discover = to find something for the first time
  • diverse = very many different kinds
  • environment = the world around us
  • equator = line that runs around the middle of the Earth
  • exist = survive, live
  • flatfish = sea fish with a thin flat body
  • generally = normally
  • global warming = the constant rise in the temperature of the atmosphere
  • guide = show
  • habitat = natural home of a plant or animal
  • hemisphere = half of the Earth
  • however = but
  • include = consist of
  • jellyfish = sea animal with a round body that can sting you
  • limit = here: are only in
  • maintain = keep up
  • mammal = animal that drinks milk from its mother when it is young
  • marine = about the world’s oceans
  • octopus = sea creature with eight arms
  • on average = normally
  • oxygen = gas that is in the atmosphere and which we need to breathe
  • partly = somewhat
  • plankton = very small forms of plants and animals that live in the sea and are eaten by other sea animals
  • provide = give
  • range = to go from one type to another
  • raw material = things that can be found naturally in our Earth and which we need , like water, oil, coal, wood etc..
  • recreation = things that we do for fun; to enjoy ourselves
  • reef = sharp line of rocks near the ocean’s surface
  • refer = to be thought of as …
  • regulate = control
  • reptile = animal, like a snake, whose body temperature always changes according to the world around it
  • research = to find out facts
  • sardine = small fish often packed in metal boxes and sold as food
  • science = knowledge about the world and nature
  • seafarer = sailor or someone who travels mostly by ship
  • shark = large sea fish with sharp teeth
  • shelf = areas of the ocean where the sea is not very deep;
  • source = basis
  • species = group of animals who live and have babies together
  • stretch = to go from one area to another
  • surface = the top layer of something
  • throughout = in all of
  • tide = the regular falling and rising of the sea
  • trench = here: narrow valley on the ocean floor
  • variety = range
  • various = different kinds of
  • vast = very large