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12.14: Aquatic Biomes

Difficulty Level: At Grade Created by: CK-12
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Is there life deep in the ocean?

Yes, there is life even at great depths in the ocean. One example of deep ocean life is this deep-sea chimaera. Chimaeras are related to sharks and resemble them somewhat. But most chimaeras are adapted for life thousands of feet under the ocean surface. This is one example of an organism that lives in an aquatic biome.

Aquatic Biomes

Recall that terrestrial biomes are defined by their climate. That's because plants and animals are adapted for certain amounts of temperature and moisture. However, would aquatic biomes be classified in the same way? No, that wouldn't make much sense—all parts of an aquatic environment have plenty of water. Aquatic biomes can be generally classified based on the amount of salt in the water. Freshwater biomes have less than 1% salt and are typical of ponds and lakes, streams and rivers, and wetlands. Marine biomes have more salt and are characteristic of the oceans, coral reefs, and estuaries.

Most aquatic organisms do not have to deal with extremes of temperature or moisture. Instead, their main limiting factors are the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water.

Marine Biomes

Aquatic biomes in the ocean are called marine biomes. Organisms that live in marine biomes must be adapted to the salt in the water. For example, many have organs for excreting excess salt. Marine biomes include the oceans, coral reefs, and estuaries (Figure below). The oceans are the largest of all the ecosystems. They can be divided into four separate zones based on the amount of sunlight. Ocean zones are also divided based on their depth and their distance from land. Each zone has a great diversity of species. Within a coral reef, the dominant organisms are corals. Corals consist partially of algae, which provide nutrients via photosynthesis. Corals also extend tentacles to obtain plankton from the water. Coral reefs include several species of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars. Estuaries are areas where freshwater streams or rivers merge with the ocean.

A kelp forest is an example of a marine biome

An example of a marine biome, a kelp forest, from Anacapa Island in the Channel Islands National Marine Sanctuary.

Freshwater Biomes

Freshwater biomes are defined by their low salt concentration, usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration, such as the ocean. There are different types of freshwater biomes: ponds and lakes (Figure below), streams and rivers, and wetlands. Ponds and lakes range in size from just a few square meters to thousands of square kilometers. Streams and rivers are bodies of flowing water moving in one direction. They can be found everywhere. They get their starts at headwaters, which may be springs, melting snow, or even lakes, and then travel all the way to their mouths, emptying into another water channel or the ocean. Wetlands are areas of standing water that support aquatic plants. Wetlands include marshes, swamps, and bogs.

Lake Tahoe in Northern California is a freshwater biome

Lake Tahoe in Northern California is a freshwater biome.

Aquatic Biomes and Sunlight

In large bodies of water, such as the ocean and lakes, the water can be divided into zones based on the amount of sunlight it receives:

  1. The photic zone extends to a maximum depth of 200 meters (656 feet) below the surface of the water. This is where enough sunlight penetrates for photosynthesis to occur. Algae and other photosynthetic organisms can make food and support food webs.
  2. The aphotic zone is water deeper than 200 meters. This is where too little sunlight penetrates for photosynthesis to occur. As a result, producers must make "food" by chemosynthesis, or the food must drift down from the water above.

Aquatic Biomes and Dissolved Substances

Water in lakes and the ocean also varies in the amount of dissolved oxygen and nutrients it contains:

  1. Water near the surface of lakes and the ocean usually has more dissolved oxygen than does deeper water. This is because surface water absorbs oxygen from the air above it.
  2. Water near shore generally has more dissolved nutrients than water farther from shore. This is because most nutrients enter the water from land. They are carried by runoff, streams, and rivers that empty into a body of water.
  3. Water near the bottom of lakes and the ocean may contain more nutrients than water closer to the surface. When aquatic organisms die, they sink to the bottom. Decomposers near the bottom of the water break down the dead organisms and release their nutrients back into the water.


  • Aquatic biomes are distinguished by the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water.
  • The photic zone extends to a maximum depth of 200 meters, while the aphotic zone is deeper than 200 meters.
  • Aquatic biomes in the ocean are called marine biomes.

Explore More

Use the resources below to answer the questions that follow.

Explore More I

  1. What factors determines the distribution of life in lakes?
  2. What is a main entry point for nutrients in the littoral zone in lakes? How does this affect the biomass of this zone? How does it affect the species diversity?

Explore More II

  1. What effect do wetlands have on water quality? How does this work?
  2. What is an estuary? How and why does the salinity of estuaries vary?


  1. Aquatic biomes are defined by what factor(s)?
  2. Distinguish between freshwater and marine biomes.
  3. How do producers in the aphotic zone differ from those in the photic zone?

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aphotic zone Area in aquatic biomes deeper than 200 meters so little light penetrates the water.
aquatic biome Biome that is based in the water, such as ponds, lakes, streams, or oceans.
chemosynthesis Process of using the energy in chemical compounds to make food; characteristic of producers in ecosystems without sunlight.
coral Marine animals typically living in compact colonies of many identical individual polyps; includes the reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.
coral reef Underwater structures made from calcium carbonate secreted by corals; colonies of tiny living animals found in marine waters that contain few nutrients.
estuary Partially enclosed body of water where fresh water from rivers and streams meets and mixes with salt water from an ocean.
freshwater biome Aquatic biome with a salt content of less than 1%; ponds and lakes, streams and rivers, and wetlands.
headwaters Source of a river or stream; the place where a river begins its journey.
marine biome Aquatic biome in the salt water of the ocean; also includes coral reefs and estuaries.
mouth Part of the river where it empties into another body of water, such as another river, lake, bay, or ocean.
photic zone Area in an aquatic biome that extends to a maximum depth of 200 meters so that at least some light penetrates the water.
photosynthesis Process by which specific organisms (including all plants) use the sun's energy to make their own food from carbon dioxide and water; process that converts the energy of the sun, or solar energy, into carbohydrates, a type of chemical energy.
wetland Land area that is saturated with water, either permanently or seasonally, with the characteristics of a distinct ecosystem.

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Difficulty Level:
At Grade
7 , 8
Date Created:
Nov 29, 2012
Last Modified:
Sep 11, 2016
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