🌊 APES Topic 1.3: Aquatic Biomes

1. Key Characteristics / Environmental Factors

These are the main abiotic (non-living) factors that determine what aquatic biomes look like, which species can survive there, and how productive they

2. Types of Aquatic Biomes & Their Zones / Examples

Here are the main aquatic biomes discussed, plus the internal zones/components, and important features / species adaptations.

A. Freshwater Biomes

• Rivers and Streams

  • Flowing water; good mixing of water and air, leading to often high dissolved oxygen.

  • Carry sediments and nutrients downstream, contributing to fertile floodplains.

• Lakes

  • Divided into zones:

  • Littoral zone: Shallow water near the shore, supporting emergent plants.

  • Limnetic zone: Open water where light reaches and photosynthesis occurs; often rich in algae & phytoplankton.

  • Profundal zone: Deeper water, too dark for photosynthesis.

  • Benthic zone: Bottom sediments where invertebrates (bugs, etc.) live in nutrient-rich material.

• Wetlands

  • Areas where soil is saturated or submerged for part of the year; shallow enough for plants to grow with roots in water.

  • Plant types: Cattails, reeds, lily pads, and other emergent vegetation, all adapted to waterlogged soils.

  • Ecosystem services / benefits: Provide flood buffering, water purification, and high productivity thanks to nutrient and organic matter accumulation in sediments.

B. Estuaries & Brackish Biomes

• Occur where freshwater mixes with saltwater (e.g., where a river meets the ocean).

• Examples: Includes mangrove swamps (in tropical climates) and salt marshes (in temperate climates).

• Adaptations: Organisms must tolerate changing salinity; plants like mangroves have special root systems (often stilt-roots) to cope with salt and waterlogging.

• Productivity: Very productive due to nutrient input from sediments, sufficient light in shallow areas, and mixing encouraging growth.

C. Marine / Oceanic Biomes

• Coral Reefs

  • Found in warm, shallow, clear waters beyond the shoreline.

  • Known for very high biodiversity.

  • A key mutualistic relationship exists between coral animals and photosynthetic algae (zooxanthellae).

  • Corals build calcium carbonate skeletons, providing structure and habitat; algae supply sugars via photosynthesis.

• Intertidal Zones

  • The narrow band of coastline between high tide and low tide.

  • Organisms must tolerate significant fluctuations: waves, exposure to air (heat, desiccation), and changing salinity.

  • Examples: Barnacles, crabs, sea stars, and other organisms that can cling to rocks or seal themselves off.

• Open Ocean (Pelagic Zones)

  • A very large biome; much of the ocean is low in nutrients and productivity per area, especially in deeper zones.

  • Zones:

  • Photic Zone: Where sunlight penetrates, allowing for photosynthesis.

  • Aphotic Zone: No sunlight; organisms rely on detritus, chemosynthesis, or predation.

  • Although productivity per area can be low, the ocean's immense size means its total contribution to global oxygen & carbon cycling is large, primarily through phytoplankton and algae.

3. Adaptations & Special Features

• Salinity Tolerance: Many aquatic organisms are adapted to varying salinity, particularly in estuaries.

• Root Adaptations: Some plants, such as mangroves, have roots specifically adapted to deal with salt and water movement.

• Intertidal Adaptations: Organisms in intertidal zones often possess strong anchoring mechanisms (to rocks), shells, or coverings to resist drying and wave action.

• Depth / Light Adaptations: Organisms in deep water typically do not rely on sunlight for energy, whereas those near the surface have adaptations for photosynthesis.

4. Ecosystem Services & Importance

• Wetlands: Provide crucial flood control, water filtration, and nutrient cycling.

• Estuaries & Coastal Zones: Serve as critical breeding grounds for fish & shellfish.

• Coral Reefs: Protect coastlines, support high biodiversity, and contribute to tourism & fisheries.