Eutrophication, Climate Change, Invasive Species

Eutrophication

• Definition: The addition of excess nutrients (e.g. sewage, fertilizers from agricultural runoff, and fossil fuel combustion) into a body of water.
• Impact on Coastal Waters: Nutrient input is a predominant form of pollution affecting coastal marine environments, leading to significant ecological changes.

Effects of Eutrophication

• Phytoplankton and Algal Bloom:
  • Excessive nutrients lead to rapid increases in phytoplankton and algal production, causing phenomena like red tides and foams.
  • Eventually, natural grazers (e.g., zooplankton, suspension feeders) can’t control these populations, resulting in harmful algal blooms (HABs).
• Hypoxia:
  • Increased biological oxygen demand (BOD) due to decaying organic matter reduces dissolved oxygen (DO), leading to hypoxic conditions (levels ≤ 2 mg O2/l).
  • Extreme cases (<0.5 mg O2/l) create “Dead Zones” causing mass mortality of marine life.

Climate Change

• Link to Marine Environment: Climate change interacts with marine ecosystems through rising greenhouse gas concentrations, altering weather patterns, and affecting salinity and nutrient availability.
• Effects on Temperature:
  • Ocean temperatures are rising due to CO2 emissions (from fossil fuels and deforestation).
  • Increased temperatures lead to changes in species distributions, loss of habitat, and alterations in food webs, affecting large predators (e.g., bluefin tuna, blue whales).

Other Climate Impact Factors

• Oxygen Levels:
  • Warmer waters hold less oxygen, stressing marine animals and potentially expanding dead zones.
• Ocean Acidification:
  • Increasing CO2 levels lead to acidification, affecting organisms relying on calcium carbonate (e.g., corals, shellfish).

Invasive Species

• Definition: Nonnative species introduced to new areas, often due to human activities like shipping or aquaculture.
• Success Factors:
  • Successful invasions often occur due to competitive advantages over native species and lack of predators.

Ecological Dominance

• Changes in Communities: Invasive species like the European green crab (Carcinus maenas) can significantly reduce populations of native species (e.g., crabs and clams).
• Transport Mechanisms:
  • Ballast Water: Ships transfer organisms along with water taken from their original port.
  • Accidental Releases: Species can be accidentally released, such as the lionfish in the Caribbean after a hurricane in Miami.

Summary of Case Studies

• Caspian Sea: The invasive ctenophore Mnemiopsis leydii introduced in the Caspian Sea significantly reduced zooplankton populations, impacting fish and seals.
• Aquaculture Impact:
  • The introduced alga Eucheuma in Hawaii caused detrimental effects on reefs, competing for space and resources.

Research References

• Key Studies: Eutrophication begins with nutrient enrichment, leading to hypoxia which has been investigated thoroughly (e.g., Diaz & Rosenberg, 2008).
• Recent Trends: Observations indicate that ocean temperatures have reached record highs (Shao, 2023), demonstrating the urgency of addressing these environmental challenges.