Rucete ✏ Campbell Biology In a Nutshell
Unit 8 ECOLOGY — Concept 52.3 Aquatic Biomes Are Diverse and Dynamic Systems That Cover Most of Earth
Aquatic biomes are classified based on physical and chemical features such as salinity, light penetration, and depth. Covering the majority of Earth’s surface, they play a crucial role in global climate regulation, oxygen production, and biodiversity.
1. General Characteristics of Aquatic Biomes
- Distinguished from terrestrial biomes by physical and chemical conditions, not vegetation
- Marine biomes (e.g. oceans): ~3% salt concentration
- Freshwater biomes (e.g. lakes, rivers): <0.1% salt
- Marine biomes cover ~75% of Earth, driving global rainfall, oxygen levels, and climate patterns
- Freshwater biomes are heavily influenced by surrounding terrestrial systems and water flow patterns
2. Zonation in Aquatic Environments
- Aquatic systems are stratified both vertically and horizontally:
- Photic zone: light penetration supports photosynthesis
- Aphotic zone: little/no light
- Together they form the pelagic zone
- Abyssal zone: deep ocean (2,000–6,000 m)
- Benthic zone: bottom substrate, home to benthos feeding on detritus
- Thermocline: narrow band where temperature rapidly shifts from warm surface water to cold deep water
3. Seasonal Turnover in Lakes
- Temperate lakes experience seasonal mixing (turnover) in spring and autumn
- Surface water warms or cools to ~4°C and sinks, mixing nutrients and oxygen throughout the water column
- In summer and winter, thermal stratification reduces mixing, creating oxygen and nutrient gradients
4. Aquatic Biome Classification
- Based on:
- Light availability (photic vs aphotic)
- Distance from shore and depth
- Open water vs bottom habitat
- Lake zones: littoral (near shore), limnetic (open water), benthic (bottom)
- Marine zones: intertidal, neritic, oceanic, benthic, abyssal
- Species distribution is limited by these abiotic gradients, especially light and depth
- Phytoplankton dominate the photic zone
- Deeper zones have fewer organisms due to lack of light and lower productivity
In a Nutshell
Aquatic biomes vary in salinity, light, and depth, and include vast ecosystems like oceans and lakes. These environments are layered vertically and seasonally mixed, influencing oxygen and nutrient flow. The physical structure of water systems determines where life can thrive, making aquatic biomes both diverse and essential to Earth’s biosphere.