7. Coral Reefs and Coral Bleaching

Case Study 1: Widespread Coral Bleaching in Little Cayman

Geographical Thought & Perspectives:

• Darwin’s Subsidence Theory (1842) – Formation of coral reefs through gradual sinking.
• Anthropogenic Climate Change (IPCC, 1988–Present) – Human-induced disruptions in marine ecosystems.
• Marine Heatwave Theory (Hobday et al., 2016) – Extreme ocean temperature anomalies impacting coral reefs.

Models/Theories/Laws:

• Coral Bleaching Threshold Model – Temperature limits beyond which corals expel symbiotic algae.
• Degree Heating Weeks (DHW) Model – Measurement of accumulated thermal stress.
• Ocean Acidification Model – Impact of CO₂ absorption on coral calcification.

Recent Data:

• Little Cayman: Experienced a marine heatwave exceeding 17 DHW, leading to mass coral bleaching.
• Bleaching Impact: ~80% of corals bleached, with 54% recorded as dead by the final survey.
• Satellite Observations: NOAA confirms global coral bleaching affecting 83.8% of reef areas worldwide.

Spatial Variation:

• Western Caribbean: Severe bleaching due to prolonged heat stress.
• Eastern Caribbean: Less impact due to deeper, cooler waters.

Temporal Variation:

• Historical Trends: Increasing frequency of bleaching events since 1998.
• Future Projections: Expected annual bleaching by 2050 due to climate change.

Source:

• PLOS One: “Widespread Coral Bleaching and Mass Mortality During the 2023–2024 Marine Heatwave in Little Cayman”
• NOAA Coral Reef Watch: “Current Global Bleaching: Status Update & Data Submission”

Insight:

Little Cayman’s coral bleaching validates marine heatwave models, emphasizing the urgent need for global climate action.

Case Study 2: Global Coral Bleaching Event Confirmed by NOAA

Geographical Thought & Perspectives:

• Darwin’s Subsidence Theory (1842) – Formation of coral reefs through gradual sinking.
• Anthropogenic Climate Change (IPCC, 1988–Present) – Human-induced disruptions in marine ecosystems.
• Marine Heatwave Theory (Hobday et al., 2016) – Extreme ocean temperature anomalies impacting coral reefs.

Models/Theories/Laws:

• Coral Bleaching Threshold Model – Temperature limits beyond which corals expel symbiotic algae.
• Degree Heating Weeks (DHW) Model – Measurement of accumulated thermal stress.
• Ocean Acidification Model – Impact of CO₂ absorption on coral calcification.

Recent Data:

• Global Bleaching Event: NOAA confirms the fourth global coral bleaching event on record.
• Affected Regions: Bleaching documented in Florida, the Caribbean, Australia’s Great Barrier Reef, and the Indian Ocean.
• Satellite Observations: NOAA’s Coral Reef Watch detects extreme heat stress across all major ocean basins.

Spatial Variation:

• Tropical Oceans: Most affected due to high sea surface temperatures.
• Temperate Oceans: Less impact due to seasonal cooling.

Temporal Variation:

• Historical Trends: Global bleaching events recorded in 1998, 2010, 2014–2017, and 2023–24.
• Future Projections: Expected increase in bleaching frequency due to warming oceans.

Source:

• NOAA: “NOAA Confirms 4th Global Coral Bleaching Event”

Insight:

The 2023–24 global coral bleaching event validates climate models, emphasizing the urgent need for mitigation strategies.