4.3D Impact on freshwater and marine ecosystems Notes

Climate Change and Ocean Acidification

Climate Change

1. Refers to long-term alterations in temperature, precipitation, wind patterns, and other aspects of the Earth’s climate system.
2. Primarily caused by human activities such as burning fossil fuels, deforestation, and industrial emissions, leading to an enhanced greenhouse effect.
3. Results in global warming, melting ice caps, sea-level rise, and disrupted oceanic currents.

Ocean Acidification

1. Occurs when excess CO₂ from the atmosphere dissolves into seawater, forming carbonic acid (H₂CO₃).
2. When CO₂ dissolves in seawater, it forms carbonic acid (H₂CO₃), which dissociates into bicarbonate (HCO₃⁻) and hydrogen ions (H⁺), reducing the availability of carbonate ions (CO₃²⁻) needed for shell and skeleton formation.
3. The pH of surface ocean water has dropped from about 8.2 to 8.1 since pre-industrial times, a 30% increase in acidity.
4. Since the Industrial Revolution, ocean pH has dropped from 8.2 to around 8.1, a 26% increase in acidity.

Effects on Marine Organisms

1. Coral Reefs: Slower calcium carbonate deposition weakens structures.
2. Shellfish: Oysters, clams, and pteropods (sea butterflies) develop thinner shells.
3. Zooplankton: Reduced availability of planktonic prey destabilizes marine food chains.
4. Fish: Acidic water interferes with sensory and reproductive systems.

Climate Change Impacts on Aquatic Ecosystems

1. Temperature Rise and Habitat Shifts

1. Warmer oceans cause species migration toward cooler waters (often poleward or deeper zones).
2. Some species fail to adapt quickly enough, leading to local extinctions or disrupted food chains.
3. Warmer water holds less oxygen, worsening hypoxic (low-oxygen) conditions.

2. Coral Bleaching

1. Corals live symbiotically with photosynthetic algae (zooxanthellae).
2. When sea temperature rises or acidity increases, corals expel zooxanthellae, losing their color, a process called bleaching.
3. Bleached corals have reduced growth and reproduction and are prone to disease and death if stressful conditions persist.

3. Ocean Acidification and Shell Formation

1. Organisms like mollusks, sea urchins, and plankton rely on calcium carbonate (CaCO₃) to build shells and skeletons.
2. Lower pH dissolves CaCO₃ or inhibits its formation, weakening these species.
3. As these species decline, entire marine food webs are destabilized, affecting everything from plankton to whales.

Case study

The Great Barrier Reef, Australia

• Located off Queensland, the Great Barrier Reef is the largest coral reef system in the world, hosting over 1,500 species of fish and 400 species of coral.
• It supports local economies through fishing and tourism, providing income for thousands.

Stress Factors:

• Rising sea temperatures cause mass bleaching events.
• Ocean acidification weakens coral skeletons and slows growth.
• Pollution and runoff from agriculture increase nutrient loads, leading to algal blooms that block sunlight.
• Cyclones and storm surges further damage coral structures.

Ecosystem Impacts:

• Biodiversity loss: coral-dependent species decline as habitats disappear.
• Economic loss: the reef generates over A$6 billion annually through tourism; bleaching reduces visitation.
• Coastal protection: weakened reefs can no longer buffer against waves and erosion.
• Food web disruption: loss of corals affects herbivores and predators alike.

Designing an Experiment: The Impact of Acidification on Shelled Organisms

Aim: To investigate the impact of acidification on shell growth in mollusks.

Method Overview:

1. Independent variable: pH of water (controlled using CO₂ bubbling).
2. Dependent variable: Shell thickness or mass of mollusks (e.g., oysters or snails).
3. Procedure:
   1. Maintain identical temperature, salinity, and light conditions.
   2. Expose identical groups to different pH levels (e.g., 8.1, 7.8, 7.5).
   3. Measure shell mass after several weeks.
4. Expected result: Lower pH → slower shell formation and thinner shells.

Mitigating Unsustainable Exploitation of Freshwater and Marine Ecosystems

1. Unsustainable exploitation occurs when aquatic resources (fish, crustaceans, etc.) are harvested faster than they can replenish.
2. Causes include overfishing, illegal fishing, bycatch, and destructive practices.
3. Sustainable management ensures continued resource availability while protecting ecosystems.

Strategies for Sustainable Management

1. Policy and Legislation

1. Governments use fisheries laws and management plans to regulate harvests and protect ecosystems.
2. Measures include:
   1. Quotas: Limit on total allowable catch (TAC).
   2. Permits: Licensing for commercial or recreational fishing.
   3. Fishing seasons: Close during breeding or migration periods.
   4. Mesh size regulations: Prevent capture of juvenile fish.
   5. Zones: Designate no-take areas or restricted-use regions.
   6. Gear restrictions: Ban harmful equipment (e.g., drift nets, bottom trawlers).

2. International Cooperation

1. Fish populations often migrate across national borders.
2. International agreements ensure shared management and responsibility.

3. Consumer Behaviour and Certification

1. Consumer awareness plays a major role in driving sustainable fisheries.
2. Eco-labels like the Marine Stewardship Council (MSC) and Aquaculture Stewardship Council (ASC) help identify sustainably sourced seafood.
3. Educating consumers to choose certified products reduces market demand for overexploited species.

4. Local and Individual Actions

1. Supporting sustainable fisheries through consumer choices (e.g., avoiding overfished species).
2. Reducing seafood waste and choosing seasonal or locally caught species.
3. Participating in community-based monitoring or citizen science programs.

Marine Protected Areas (MPAs)

1. Marine Protected Areas (MPAs) are clearly defined zones of oceans, seas, estuaries, or lakes where human activities are regulated or restricted to conserve biodiversity, protect habitats, and maintain sustainable yields.
2. MPAs range from small no-take reserves to vast multi-use zones managed for both conservation and economic sustainability.

Functions and Importance of MPAs

1. Protect critical habitats, such as coral reefs, mangroves, and seagrass meadows.
2. Provide spawning and nursery grounds, allowing fish populations to replenish.