Chapter 6: Human Disruption and Degradation of Marine Ecosystems

Concept $6.3$ : Human activities threaten aquatic biodiversity and disrupt the essential ecosystem and economic services provided by marine systems.
Targeted Ecosystems: Major disruption and degradation are occurring in coastal marshes, shorelines, mangrove forests, and coral reefs.
Mangrove Deforestation (World Wildlife Fund Data): More than $35\%$ of the original global mangrove forest area has been lost due to:
- Agricultural and urban expansion.
- Construction of marinas and roadways.
- General coastal development.
Mangrove Extinction Risk (IUCN Data): According to the International Union for the Conservation of Nature, more than $1$ in every $6$ mangrove species is in danger of extinction.
Seagrass Bed Loss: Since $1980$ , approximately $29\%$ of the world’s seagrass beds have been lost due to pollution and various other disturbances.
Human Footprint on Oceans: A $4$ -year study by an international team of scientists revealed that human activities have heavily affected $41\%$ of the total world ocean area.
Coastal Population Pressure: Human impact increases proportionally with population density near coasts. Current demographics show:
- Approximately $45\%$ of the world's population lives along or near coasts.
- More than half of the population (generally) resides in coastal areas.
- These percentages are currently on the rise.

Climate Change as a Principal Threat:
- Mechanism: Land-based glaciers (such as those in Greenland) are melting, and warmer ocean waters are undergoing thermal expansion.
- Consequences: Sea levels are rising. Projected rises for this century threaten to:
  - Destroy many shallow coral reefs.
  - Flood coastal marshes and other coastal ecosystems.
  - Submerge various coastal cities.
Ocean Acidification:
- Significance: Some scientists prioritize the threat of ocean acidification over climate change.
- Targeted Organisms: It is specifically threatening to coral reefs, phytoplankton, and shellfish.
- Biological Impact: Many of these organisms form their protective shells and structures from calcium carbonate, which is hindered in acidic conditions.

General Marine Ecosystem Impacts:
- Loss of half ( $50\%$ ) of coastal wetlands to agriculture and urban development.
- Loss of over one-fifth ( $20\%$ ) of mangrove forests to agriculture, aquaculture, and general development.
- Erosion of beaches resulting from both development and rising sea levels.
- Degradation of ocean-bottom habitats caused by dredging and the use of fishing trawlers.
Specific Impacts on Coral Reefs:
- Damage status: At least $20\%$ of coral reefs are severely damaged; an additional $25{-}33\%$ are currently threatened.
- Environmental Stressors: Ocean warming, rising ocean acidity, and rising sea levels.
- Pollutant Stressors: Soil erosion and excessive algae growth stemming from fertilizer runoff.
- Direct Human Damage: Bleaching, increased Ultraviolet (UV) exposure, and physical damage from anchors, fishing, and diving.

Coastal Development: Directly destroys or degrades critical coastal habitats.
Pollutant Runoff: Includes fertilizers, pesticides, and livestock wastes.
Maritime Pollution: Specifically pollution originating from cruise ships and oil tanker spills.
Overfishing: Leads to the depletion of commercially viable fish species populations.
Destruction via Fishing Trawlers: These vessels drag weighted nets across the ocean floor, causing catastrophic damage to bottom habitats.
Invasive Species: Competition and predation from invasive species deplete populations of native species.

Enric Sala (Marine Biologist and National Geographic Explorer):
- Professional focus: Working to protect undisturbed marine ecosystems and learning what oceans were like before human disruption.
- Key Finding: Research in the Southern Line Islands (South Pacific) confirmed that humans are the most important factor determining the health of coral reefs.
- Cause of Reef Death: A combination of local impacts (fishing and pollution) and global human-induced climate change.
The Pristine Seas Project ( $2008$ ):
- Goal: To find, survey, and protect the last wild places in the ocean.
- Objectives: Creating representative examples of protected ecosystems to ensure they remain healthy, productive, and resilient against warming and acidification.
Conservation Strategy and Achievements:
- Philosophy: "Take out less and throw in less."
- Marine Protected Areas (MPAs): Establishing large areas of ocean habitat entirely free of human activities.
- Impact: To date, the project has helped create $9$ of the planet's largest marine reserves.
- Scope: These reserves cover over $3\,million\,km^2$ , which is more than $6 \times$ the area of Spain.
- Future Targets: Target $12$ more locations to achieve a goal of protecting $20$ of the wildest ocean places.

Checkpoint for Understanding $6.3$ :
- Question 1: Identify the greatest threats to marine ecosystems.
- Answer: Climate change (leading to rising sea levels) and ocean acidification are the primary threats, supplemented by coastal development, pollution runoff, overfishing, habitat destruction by trawlers, and invasive species.
- Question 2: Explain why ocean acidification is a serious threat to coral reefs, phytoplankton, and shellfish.
- Answer: These organisms rely on calcium carbonate to build their shells and skeletons; acidification reduces the availability of carbonate ions or can even dissolve the structures already formed.
Thinking About Coral Reef Destruction:
- Prompt: How might the loss of most remaining tropical coral reefs affect future generations, and what can be done?
- Consideration: Loss of reefs affects biodiversity and food security for children/grandchildren; actions include reducing individual carbon footprints and supporting the establishment of large-scale marine reserves.