Aquatic Biomes Notes

Aquatic Biomes

• Aquatic environments make up the largest portion of the biosphere, covering approximately 75% of the Earth's surface.

Water Volume in the Biosphere

• 97.5% is in oceans.
• 2.5% is freshwater, including glaciers, polar ice caps, lakes, rivers, and groundwater.

Categorization of Aquatic Biomes

• Based primarily on abiotic characteristics such as:
  • Salinity
  • Depth
  • Currents

Main Categories of Aquatic Environments

• Divided based on salinity:
  • Freshwater
  • Saltwater (or marine)

Examples of Aquatic Biomes

• Lakes
• Reefs
• Rivers
• Pelagic zones
• Benthic zones
• Estuaries
• Intertidal zones

Hydrologic Cycle

• All aquatic biomes are directly or indirectly linked as components of the hydrologic cycle.

Hydrologic Cycle Components

• Precipitation over land and ocean
• Transport of water vapor
• Solar energy over land
• Movement of water vapor by wind
• Evaporation from the ocean
• Infiltration through the soil
• Transpiration from land
• Surface runoff and groundwater

Abiotic Factors Affecting Aquatic Ecosystems

• Solar radiation
• Temperature
• Nutrient availability

Common Characteristics of Aquatic Biomes

• More moderate temperatures compared to terrestrial biomes.
• Light penetration decreases rapidly with depth.
• Nutrients tend to concentrate at the bottom.

Stratification in Aquatic Biomes

• Many aquatic biomes are stratified into zones or layers defined by:
  • Light penetration
  • Temperature
  • Depth

Light Penetration and Stratification

• Stratification (vertical structure) based on light penetration:
  • Photic Zone: The upper zone where light penetrates and photosynthesis can occur.
  • Aphotic Zone: The intermediate zone where light does not penetrate.
  • Benthic Zone: The bottom zone where decomposition is most active.

Lake Stratification and Zonation

• Littoral Zone
• Limnetic Zone
• Photic Zone
• Pelagic Zone
• Benthic Zone
• Aphotic Zone

Marine Stratification and Zonation

• Pelagic Zone
• Photic Zone (0-200m)
• Neritic Zone
• Oceanic Zone
• Aphotic Zone (200m-2,000-6,000m)
• Benthic Zone
• Intertidal Zone
• Continental Shelf
• Continental Barrier

Coral Reefs

• Corals are colonial animals.
• Corals secrete an external skeleton composed of calcium carbonate ($CaCO_3$) on which they grow.
• Corals feed on zooplankton suspended in the water.
  • Zooplankton covers only 10% of their energy needs.
  • The remaining 90% comes from organic molecules produced by symbiotic zooxanthellae (protists) via photosynthesis.
• Coral reefs consist of calcareous structures formed by the accumulation of coral skeletons.
• Due to the mutualistic relationship with photosynthetic zooxanthellae, the distribution of corals is limited to clear waters with depths less than 45 meters (148 feet) where there is sufficient light.
• Precipitation of calcium, necessary for the formation of the calcareous exoskeleton of corals, occurs when:
  • Water salinity and temperature are high (between 20°C and 28°C / 68°F and 82°F).
  • The concentration of $CO_2$ is low.
• Coral reefs are found in warm, shallow waters near coasts in tropical and subtropical zones (between the Tropic of Cancer and the Tropic of Capricorn).
• Coral reefs constitute less than 1% of the total area of the world's oceans, but they provide a great diversity of habitats and contain a great diversity of species.