Big Picture

Biomes are areas that have similar abiotic and biotic factors. The biome may be terrestrial or aquatic. Terrestrial biomes are mainly affected by the climate, which influences plant life, biodiversity, and the ability to adapt. The different aquatic biomes are usually based on the amount of available sunlight and concentrations of dissolved oxygen and other nutrients in the water.

Key Terms

Biome: Climatically and geographically similar areas with similar conditions on the Earth. This includes communities of plants, animals, and soil organisms.

Terrestrial Biome: A biome on land.

Aquatic Biome: A biome surrounding or in water

Climate: The average weather conditions in any given area over a long period of time. It is described in terms of temperature and moisture.

Growing Season: The period of time each year when it is warm and wet enough for plants to grow successfully.

Dormancy: A state in which a plant slows down its cellular activities and may shed its leaves.

Photic Zone: Area in aquatic biomes that goes as deep as 200 meters (656 feet) below the surface of the water.

Aphotic Zone: Area in aquatic biomes that is below 200 meters (656 feet).

Marine Biome: Aquatic biome located in the ocean.

Salinity: The saltiness of a body of water. It usually refers to the amounts of sodium chloride, bicarbonates, magnesium, and calcium sulfates in water.

Intertidal Zone: In marine biomes, the narrow strip along the coastline that is covered by water at high tide and exposed to air at low tide.

Freshwater Biome: An aquatic biome that has little or no salt.

Wetland: Area that is saturated with water or covered by water at least one season annually.

Estuary: A body of water that has both saltwater and freshwater.

Terrestrial Biomes

Terrestrial biomes are biomes on land. The main features of terrestrial biomes are influenced by climate, with temperature and moisture being the two most important abiotic factors.

  • Producers at the bottom of the trophic pyramid influence the biodiversity and the number of other organisms in the biome. In terrestrial biomes, plants are the main producers.
  • The number and variety of plants are affected by the length of the growing season. Tropical rainforests have long growing seasons and very high biodiversity
  • Plants adapt to cold regions by entering dormancy. Animals also have adaptations for cold weather, like thick fur and blubber.

Generally, temperature drops as we move from the equator to the two poles. We can describe major temperature zones based on how far north or south the region is from the equator. This can be seen in the map next page.

The following are seven of the most widely reoccurring biomes:

  • Tropical rain forest
  • Savanna
  • Taiga
  • Tundra
  • Desert
  • Temperate grassland
  • Temperate forest (deciduous and evergreen)

Climate is different from weather. Weather is used for day-to-day conditions (such as checking the weather conditions for the week), while climate is over a longer period of time.



Biomes cont.

World Map of Biomes

World Map of Biomes
Image credit: CK-12 Foundation, CC-BY-NC-SA 3.0

Aquatic Biomes

Aquatic biomes are not as affected by temperature and climate. Instead, the two most important abiotic factors that affect aquatic biomes are the availability of sunlight and the concentration of dissolved oxygen and other nutrients in the water

For large bodies of standing water, the water can be divided into the following zones:

  • Photic zone: Sunlight penetrates enough for photosynthesis to occur. Organisms live in a higher density and number in the photic zone than the aphotic zone.
  • Aphotic zone: Below 200 meters (656 feet), photosynthesis is not possible. Food must be made by chemosynthesis or else drift down from the water above.

The types of aquatic organisms found in the aquatic biome differ depending on where they live.

  • Plankton: Tiny aquatic organisms that cannot move on their own. They live in the photic zone.
  • Phytoplankton: Bacteria and algae that use photosynthesis to make food.
  • Zooplankton: Plankton that feeds on phytoplankton.
  • Nekton: Aquatic organisms that move on their own within water. They are found both in the photic zone and abiotic zone. They feed on plankton or other nekton. Shrimp and fish are categorized as nekton.
  • Benthos: Aquatic organisms that crawl on the bottom of the water. Many are decomposers. Benthos include sponges and clams.

Aquatic biomes include:

Marine biome
  • Organisms in marine biomes must adapt to the salinity.
  • Organisms living in the intertidal zone along the coastline also need to adapt to the constantly changing temperature and the force of water moving in and out.
  • In the deepest parts of the ocean, organisms must be able to withstand extreme water pressure, cold water, and complete darkness. To counter such factors, organisms cluster around hydrothermal vents in the ocean floor that release hot water.
Freshwater biome
  • Organisms in freshwater biomes don’t have to worry about salinity.
  • Includes standing or running freshwater.
  • Plants and plankton are the primary producers in standing water, while algae and plants are the primary producers in running water.
  • Either saltwater or freshwater saturates an area at least one season a year.
  • Wetlands are important biomes because they store excess water from floods, prevent erosion and slow runoff, remove excess nutrients from runoff, provide a unique and safe habitat for communities of plants and many species of animals.



Aquatic Biomes Cont.

  • The estuary has one or more rivers feeding into it and is also connected to the ocean.
  • Usually found along the coast, estuaries have both fresh-water and saltwater.
  • They are very biologically productive regions with high bio-diversity.