4.3 Aquatic food production systems

Role of Phytoplankton and Macrophytes in Food Webs

• Phytoplankton (Microscopic Algae):
  • Primary Producers: Perform photosynthesis, forming the base of aquatic food webs.
  • Oxygen Production: Generate ~50% of the world's oxygen.
  • Nutrient Cycling: Uptake carbon dioxide and nutrients, influencing the global carbon cycle.
  • Support for Marine Life: Serve as the main food source for zooplankton, which are consumed by fish, whales, and other marine organisms.
• Macrophytes (Large Aquatic Plants):
  • Habitat Creation: Provide shelter and breeding grounds for fish and invertebrates.
  • Nutrient Regulation: Absorb excess nutrients, reducing eutrophication risks.
  • Food Source: Directly consumed by herbivorous species like manatees and indirectly supports detritivores via decaying organic matter.

Consequences of Increased Demand for Seafood

1. Overfishing: Depletion of fish stocks, threatening ecosystem balance.
2. Bycatch: Accidental capture of non-target species (e.g., dolphins, sea turtles).
3. Ecosystem Disruption: Removal of keystone species destabilizes food webs.
4. Economic Pressure: Increased competition for dwindling resources affects the livelihoods of fishing communities.

Increased demand for seafood has caused overexploitation of certain species.

Consequences of Overexploitation

1. Biodiversity Loss: Decline in species populations and genetic diversity.
2. Trophic Cascades: Imbalances in food webs, such as increased populations of prey species when predators are overfished.
3. Economic Impact: Collapse of fisheries, reducing food security and income for millions.
4. Habitat Destruction: Trawling and other unsustainable practices damage seabeds and coral reefs.

Maximum Sustainable Yield (MSY)

Maximum sustainable yield is the largest catch that can be sustainably harvested from a species' population without depleting its long-term potential. MSY depends on the reproductive rates and population size of the species. Its calculation requires accurate fish stock assessments and monitoring.

MSY can be demonstrated in a graph.

Risks of Harvesting Fish at MSY (HL)

There are risks in harvesting fish at the maximum sustainable yield (MSY) rate and these risks need to be managed carefully. The MSY is only an estimated value and attempting to harvest at exactly that rate will inevitably be inaccurate. Exceeding the rate may lead to a reduction in reproductive potential and positive feedback, causing a rapid decline in fish stocks

Marine Protected Areas (MPAs)

Unsustainable exploitation of freshwater and marine ecosystems and organisms can be mitigated through policy legislation addressing the fishing industry and changes in consumer behaviour. One such action can be the establishment of Marine Protected Areas. They are the regions of oceans or coasts designated for protection to conserve biodiversity and promote sustainable use.

Benefits:

• Replenishes fish stocks by providing safe breeding grounds.
• Protects vulnerable species and habitats.
• Enhances resilience of marine ecosystems to climate change.

Aquaculture

Aquaculture is the farming of aquatic organisms like fish, molluscs and aquatic plants. It has been increasing to meet the increased need for food and has supported economic growth, but it is associated with negative environmental impacts.

Advantages:

• Reduces pressure on wild fish stocks.
• Provides a consistent food supply.

Challenges:

• Pollution from waste and chemicals.
• Escaped farmed species may outcompete wild populations.
• Escape farmed species can spread diseases

Conserving Overexploited Fishes (HL)

Overexploited species may recover with cooperation between governments, the fishing industry, consumers and other interest groups. However, their different perspectives on the need for conservation and methods need to be resolved.

Some conservation methods can be:

1. Regulations: Enforcing fishing quotas and seasonal bans.
2. Restocking Programs: Releasing hatchery-raised fish into the wild.
3. Community Involvement: Empowering local fishers to manage resources sustainably.

Some different perspectives on conservation among stakeholders can be:

• Fishers: Concerned about income and job security but benefit from long-term conservation.
• Environmentalists: Advocate for stricter protections to preserve biodiversity.