Ecology & the Biosphere Notes

52.3: Aquatic Biomes

• Aquatic biomes are diverse and dynamic systems covering most of Earth.
• They are characterized by their physical and chemical environment.

Salinity Levels

• Marine biomes: ~3% salt, average of 34 parts per thousand (ppt).
• Freshwater biomes: <0.1% salt, range of 0.1 – 0.4 ppt.
• Hypersaline waters: >50 ppt; desert pupfish can tolerate up to 70 ppt.

Zones of the Ocean

• Intertidal zone: Shoreline areas periodically submerged and exposed.
  • Challenging habitat with variations in temperature and salinity, plus mechanical forces of wave action.
  • Oxygen and nutrient levels are high.
  • Substrates are generally rocky or sandy.
• Neritic zone: Shallows over the continental shelf near the shore.
  • Where coral reefs and kelp forests are found.
• Coral Reefs:
  • Formed by calcium carbonate skeletons of corals.
  • Exceptionally high biodiversity.
  • Threatened by collection of corals, overfishing, climate change, pollution, and coastal development.
  • Example: Great Barrier Reef experienced widespread coral bleaching.
• Oceanic zone: Oceanic regions beyond the continental shelf.
• Photic zone: Sufficient light for photosynthesis.
• Aphotic zone: Insufficient light for photosynthesis.
• Pelagic zone: Open ocean, away from the bottom.
  • High oxygen levels, constantly mixed by wind-driven oceanic currents.
  • Seasonal turnover in temperate oceans brings nutrients from the bottom up to photic zones.
  • Nutrient levels in photic zones are low in tropical areas due to year-round thermal stratification.
  • Phytoplankton and zooplankton are the dominant organisms.
• Abyssal zone: Deep ocean, 2,000 to 6,000 m.
• Benthic zone: Seafloor (benthos = benthic communities).
  • Deep areas are cold, with no sunlight and high pressure.
  • Some organisms around hydrothermal vents are not tied to sunlight for energy.
  • Chemoautotrophs are the basis of the food chain instead of photoautotrophs in some parts of the deep benthic zone.

Aquatic Biomes: Lakes

• Standing bodies of water.
• Zones of a lake:
  • Littoral zone: Close to shore, high light, many plants.
  • Limnetic zone: Deep, lacks rooted plants, many phytoplankton, zooplankton.
  • Photic zone: Sufficient light for photosynthesis.
  • Aphotic zone: Insufficient light for photosynthesis.
  • Benthic zone: Sea floor (benthos = benthic communities).
  • Pelagic zone: Open lake, away from the bottom.
• Temperate lakes have seasonal turnover, leading to nutrient upwelling.
• Oligotrophic lakes: Nutrient-poor, oxygen-rich.
• Eutrophic lakes: Nutrient-rich, often depleted of oxygen in deep zones or throughout.

Wetlands

• Inundated at least part-time, supporting plants adapted to water-saturated soil.
• Rapid plant growth and decomposition often deplete oxygen.
• Highly impacted by humans.
• Valuable for filtering pollution and providing a barrier to flooding.

Streams and Rivers

• Have current.
• Headwaters: Cold, clear, turbulent, swift, and oxygen-rich.
• Downstream waters: Generally warmer, more turbid, and slower-moving.

Estuaries

• Transition area between river and sea.
• Salinity varies spatially and with the rise and fall of the tides.
• Estuaries are nutrient-rich and highly productive. Remember that $(\sqrt{9} = 3)$