1.3 Aquatic Biomes

Aquatic Biomes

Biomes are the broadest ecological classification and include ecosystems, communities, populations, and organisms.

Aquatic biomes are classified mainly by:

  • Salinity

  • Depth

  • Light availability

  • Water flow

  • Nutrient availability

Two main categories:

  • Freshwater biomes

  • Marine biomes

Freshwater Biomes

Freshwater makes up about 2.5% of Earth’s total water and is found on every continent.

Types of Freshwater Biomes

  • Streams

  • Rivers

  • Ponds

  • Lakes

  • Wetlands

Streams & Rivers

Flowing freshwater (lotic systems)

Characteristics:

  • Begin at springs or melting snow/ice

  • Constant movement prevents thermal stratification

  • High dissolved oxygen due to turbulence

  • Few producers; energy often comes from surrounding land (leaf litter)

Changes from source to mouth:

  • Headwaters: cold, clear, fast-flowing, rocky bottom, low nutrients

  • Downstream: warmer, slower, higher turbidity, more nutrients, muddy bottom

Ponds & Lakes

Standing freshwater (lentic systems)

Characteristics:

  • Surrounded by land

  • Can stratify by temperature in deeper lakes

  • Oxygen higher near surface, lower at depth

Lake Zones

  • Littoral zone: shallow near shore, sunlight reaches bottom, most plant life

  • Limnetic zone: open surface water, sunlight present, phytoplankton dominant

  • Profundal zone: deep water below light penetration, no photosynthesis

  • Benthic zone: bottom sediments at all depths, decomposers present

Lake Productivity

  • Oligotrophic: low nutrients, clear water, low productivity

  • Mesotrophic: moderate nutrients and productivity

  • Eutrophic: high nutrients, algal blooms, low oxygen

Freshwater Wetlands

Areas with soil saturated with water for all or part of the year

Types:

  • Marshes

  • Swamps

  • Bogs

Characteristics:

  • Shallow water

  • Very high productivity

  • High biodiversity

  • Filter pollutants and excess nutrients

  • Reduce flooding

Differences:

  • Marshes: grasses, few or no trees

  • Swamps: trees and grasses

  • Bogs: acidic, lower productivity

Marine Biomes

Marine biomes cover about 70% of Earth’s surface and have high salinity.

Types:

  • Oceans

  • Coral reefs

  • Estuaries

  • Salt marshes

  • Mangrove swamps

  • Intertidal zones

Oceans (Open Ocean / Pelagic)

Largest biome on Earth

Characteristics:

  • High salinity (~3.5%)

  • Stratified by depth and light

  • Most oxygen produced by marine algae

Vertical Zones:

  • Photic zone: sunlight present, photosynthesis occurs

  • Aphotic zone: no sunlight, no photosynthesis; chemosynthesis near vents

Horizontal Zones:

  • Pelagic zone: open water

  • Benthic zone: ocean floor

Coral Reefs

Found in warm, shallow tropical waters

Characteristics:

  • Extremely high biodiversity

  • Built by corals that secrete calcium carbonate

  • Corals have symbiotic algae (zooxanthellae) that provide energy via photosynthesis

  • Require clear, warm, low-turbidity water

Types:

  • Warm-water reefs: tropical, shallow

  • Cold-water reefs: deep (200–1000 m), no photosynthesis, rely on organic material

Estuaries

Areas where freshwater rivers meet the ocean

Characteristics:

  • Brackish water with fluctuating salinity

  • Very high productivity

  • Nursery grounds for fish and shellfish

  • Filter pollutants before reaching oceans

Salt Marshes

Coastal wetlands in temperate regions

Characteristics:

  • Dominated by salt-tolerant grasses

  • Tidal influence

  • High biodiversity and productivity

  • Trap sediments and store carbon

Mangrove Swamps

Coastal wetlands in tropical and subtropical regions

Characteristics:

  • Salt-tolerant trees with submerged or aerial roots

  • Stabilize coastlines

  • Provide habitat for many species

  • Protect against erosion and storm surge

Intertidal Zone

Area between high and low tide

Characteristics:

  • Alternates between submerged and exposed

  • Extreme conditions: changing salinity, temperature, moisture

  • Organisms must be highly adapted

Abiotic Factors in Aquatic Biomes

Affect both freshwater and marine systems:

  • Salinity

  • Depth

  • Light availability

  • Temperature

  • Velocity (flow rate)

  • Dissolved oxygen

  • Nutrients (nitrates, phosphates)

  • Turbidity

  • Suspended matter

  • Bottom substrate (sand, rock, mud)

Marine Productivity Patterns

  • High near coasts due to sunlight and nutrient input

  • Upwelling zones bring deep, nutrient-rich water to surface

  • Cold water often has high dissolved oxygen

Human Impacts on Aquatic Systems

  • Agricultural and industrial runoff pollutes water

  • Excess nutrients cause eutrophication

  • Dams alter flow and disrupt ecosystems

  • Wetland loss increases flooding

  • Climate change increases storm intensity

  • Freshwater becomes contaminated or saline faster than it is replenished

  • Desalinization is possible but expensive