Aquatic Biomes | Biology

Summary: Aquatic Biomes

Aquatic biomes make up the largest share of the biosphere by area. Their characteristics depend on factors such as salinity, temperature, and light. Unlike terrestrial biomes, they do not closely follow latitude.

Two Broad Categories

• Marine biomes include oceans, coral reefs, and estuaries. They cover most of Earth’s surface and typically have a salt concentration of about 3%.
  • Marine algae absorb substantial amounts of carbon dioxide and contribute much of the world’s oxygen supply.
  • Evaporation from seawater helps supply rainfall to land.
• Freshwater biomes include lakes, rivers, streams, and wetlands. They contain less than 0.1% salt and make up only a small fraction of Earth’s water.
  • Their chemical makeup is influenced by surrounding soils and plant life.
  • Their proximity to human development makes them especially vulnerable to pollution and overuse.

Light and Aquatic Layers

Aquatic environments have layers shaped partly by how far sunlight penetrates. Photosynthetic organisms are concentrated in the photic zone, where enough light is available.

The transcript refers to a deep, dark layer as the “benthic zone,” but that description may be a captioning error: benthic generally refers to the bottom region, while the dark layer below sunlight penetration is usually called the aphotic zone. Different light and temperature conditions support different organisms.

Major Aquatic Biomes

• Lakes: Standing bodies of water, usually freshwater, often with warmer shallow water and colder deep water. Their salinity, oxygen, and nutrient levels vary. Nutrient-rich runoff from urban and agricultural areas can cause eutrophication: algal blooms grow, then oxygen levels fall, harming aquatic life.
• Rivers and streams: Flowing freshwater bodies that generally run from a source in higher, cooler areas toward a mouth, where they empty into a larger body of water.
• Wetlands: Areas saturated with water either periodically or permanently. They filter pollution, support abundant photosynthetic life, and are highly productive. Draining and filling them for development threatens these habitats.
• Estuaries: Places where rivers meet the ocean and fresh and salt water mix. Their salinity changes with the tides, so resident organisms must tolerate a wide range of salinities. River-borne nutrients support high productivity, including grasses, phytoplankton, invertebrates, fish, and birds. Estuaries are important feeding areas but are threatened by habitat loss and urban development.
• Intertidal zones: Coastal areas between land and sea that are alternately exposed to air and submerged as tides rise and fall. Species are distributed according to how well they tolerate exposure and submersion. Algae and seagrass are primary producers; organisms such as sea anemones, urchins, and sea stars live there. Pollution and development affect this zone, which is readily accessible to people.
• Open ocean: The largest aquatic biome. Vast quantities of floating plankton carry out nearly half of global photosynthesis. The open ocean also supports large schools of fish, sea turtles, dolphins, and whales. Pollution and overfishing have depleted fish populations.

Speakers and Sources

• Narrator: Jessica Pamment, identified in the video metadata as a DePaul University lecturer.
• Source: Course Hero video, “Aquatic Biomes | Biology.”