Perch in giant kelp forest Click on image for full size (425 Kb) Courtesy of NOAA

The ocean holds the largest of all biomes on Earth. It covers 70% of the planet’s surface.

Life in the ocean is diverse. The smallest creatures that call the ocean home are microscopic and made of a single cell. The largest creatures are blue whales, which can be as much as 34 meters (110 feet) long. There are many different ways to live in the ocean too. Some animals travel thousands of miles through ocean water while others stay in the same place on the ocean floor for their entire lives. Some burrow beneath the sand while others float near the water surface.

The ocean is not uniform, nor is the marine life within it.  While life in the ocean is often described as one biome, there are actually many specific ecosystems within the ocean that are characterized by physical conditions such as water temperature, the amount of sunlight that penetrates through the water, and the amount of nutrients.

Sunlight penetrates the top layer of ocean water, as much as 200 meters (656 feet) deep. This allows phytoplankton, algae, and plants like seagrass to make their own food through the process of photosynthesis. Almost all marine life (about 90%) lives within this top, sunlit layer of the ocean. Photosynthesizing organisms are the start of most marine food chains except for those in the deep ocean where there is no sunlight.

The temperature of ocean water varies depending on its location. Closer to the Earth’s polar regions, ocean water is colder. Closer to the equator, ocean water is warmer. Water that is deep in the ocean is colder than water that is near the ocean surface. Many animals can only survive at certain temperatures.  Other animals in the ocean are able to survive at a range of temperatures and can live in more places in the world’s ocean basins.

The following links give a broad overview of four different environments where life flourishes in the ocean.  Within these areas, a variety of specific ecosystems exist such as coral reefs, kelp forests, and hydrothermal vents.

• Life in the Intertidal Zone - Where the ocean meets the land, hardy animals, plants, and algae make their homes between the low tide and high tide levels.
• Life in the Open Ocean – The largest area of the marine ecosystem, the open ocean is home to swimming fish, drifting plankton, and other creatures.
• Life in the Shallow Ocean – In the sunlit parts of the shallow ocean, many animals, plants, and algae thrive on the seafloor as fish zoom above.
• Life in the Deep Ocean – This cold, dark world is home to some very unusual extreme environments where animals and bacteria have found ways to survive.