Threats to Coral Reefs as an Example of Potential Ecosystem Collapse
- Coral reefs are among the most biologically diverse ecosystems on Earth, providing crucial habitats for thousands of marine species.
- These ecosystems rely on the health of coral polyps, which are tiny organisms that build calcium carbonate skeletons, creating the structure of the reef.
- Healthy coral reefs also support fisheries, provide coastal protection, and offer economic resources through tourism.
Coral reefs are among the most biodiverse ecosystems on Earth, often called the rainforests of the sea.
Coral Bleaching: A Breakdown of Symbiosis
What Causes Coral Bleaching?
- Coral bleaching occurs when corals expel the zooxanthellae living in their tissues.
- Without these algae, corals lose their color and their primary source of energy.
Zooxanthellae are photosynthetic algae that live in coral tissues, providing nutrients through photosynthesis.
Why Do Corals Expel Zooxanthellae?
- Increased Water Temperature: Even a rise of 1–2°C above normal can trigger bleaching.
- Other Stressors: Pollution, overexposure to sunlight, and changes in salinity can also contribute.
- In 2016, the Great Barrier Reef experienced a severe bleaching event due to a prolonged marine heatwave, affecting over 90% of its corals.
- The reef's biodiversity has been significantly affected, with a reduction in fish populations, invertebrates, and other marine species.
Can Bleached Corals Recover?
- If stressful conditions persist, corals may die, leading to the collapse of the reef ecosystem.
- However, if conditions improve, corals can sometimes regain their zooxanthellae and recover.
- A common misconception is that bleached corals are dead.
- While bleaching is a sign of stress, corals can recover if conditions return to normal.
Ocean Acidification: A Hidden Threat
How Does Ocean Acidification Occur?
- When carbon dioxide ($CO_2$) dissolves in seawater, it forms carbonic acid, which lowers the ocean's pH.
- This process is called ocean acidification.
Why Is Ocean Acidification Harmful to Corals?
- Corals build their skeletons from calcium carbonate ($CaCO_3$).
- Acidic waters reduce the availability of carbonate ions, making it difficult for corals to grow and maintain their structures.
- Ocean acidification not only slows coral growth but also weakens existing structures, making them more susceptible to erosion and damage.
Since the Industrial Revolution, ocean pH has dropped from approximately 8.2 to 8.1, representing a 30% increase in acidity.
TipTo remember the effects of ocean acidification, think of it as osteoporosis for corals as it weakens their skeletons, making them fragile.
The Domino Effect: Ecosystem Collapse
Why Are Coral Reefs Important?
- Biodiversity Hotspots: Reefs support about 25% of all marine species.
- Coastal Protection: They act as natural barriers against storms and erosion.
- Economic Value: Reefs contribute to fisheries, tourism, and livelihoods for millions of people.
What Happens When Reefs Collapse?
- Loss of Habitat: Many species depend on corals for shelter and breeding grounds.
- Food Web Disruption: The decline of coral-dependent species affects predators and other interconnected organisms.
- Economic Impact: Fisheries decline, and tourism suffers, affecting coastal communities.
- How does the collapse of coral reefs highlight the interconnectedness of ecosystems?
- Can you think of other ecosystems where a single change could have cascading effects?
Addressing the Threats
Mitigation Strategies
- Reducing Greenhouse Gas Emissions: Slowing climate change is critical to stabilizing ocean temperatures and acidity.
- Marine Protected Areas (MPAs): Protecting reefs from overfishing and pollution can enhance their resilience.
- Restoration Projects: Initiatives like coral gardening and artificial reefs aim to restore damaged areas.
The Coral Restoration Foundation in Florida has successfully replanted thousands of corals, helping to rebuild damaged reefs.
Self review- What causes coral bleaching, and how does it affect the health of coral reefs?
- How does ocean acidification impact coral calcification?
