Crisis in Coral Ecosystems: Elevated Heat Stress in the Summer of 2023 Poses Serious Risks

In the year 2023, a significant increase in oceanic temperatures, exacerbated by human-induced climate change and the natural El Niño phenomenon, posed grave threats to coral reefs, notably in the vicinities of Florida, Cuba, and the Bahamas. Satellite information revealed considerable probabilities of coral bleaching and high mortality rates in these areas by the middle of October.

The marine environments surrounding Florida, Cuba, and the Bahamas experienced considerable elevations in heat stress starting in the summer of 2023, with adverse effects on the well-being of coral ecosystems.

For an extended period in 2023, the temperatures of the world’s ocean surfaces achieved unprecedented highs. This increase was driven by years of anthropogenic global warming, further aggravated by the recent activity of the natural climate variable, El Niño. Certain regions, particularly the waters around Florida, Cuba, and the Bahamas, experienced especially elevated temperatures, which negatively impacted coral reef health.

Consequences for Coral Ecosystems

Corals thrive within a narrow range of temperatures and undergo stress when water temperatures deviate excessively from this range. Coral bleaching occurs when stressed corals eject the symbiotic algae residing within them, leading to a loss of coloration. Severe bleaching events can render coral reefs vulnerable to starvation, infectious diseases, and even demise. Diver observations in the Florida Keys have confirmed that the marine thermal anomalies in the summer of 2023 led to extensive coral bleaching.

This visual representation details the progression of heat stress accumulation from July to September 2023.

Utilizing Satellite Data for Coral Surveillance

Satellite data serves as a valuable tool for assessing coral stress levels. The aforementioned visual representation illustrates the increase in accumulated heat stress from July through September 2023. The colors represent “degree heating weeks” (°C-weeks), a metric that estimates the gravity and duration of thermal stress. The data for this metric is aggregated by NOAA’s Coral Reef Watch, which combines observations from polar orbiting satellites like NASA-NOAA Suomi NPP and geostationary satellites such as GOES, supplemented by computational models.

When the accumulated heat stress achieves a value of 4, it can result in significant coral bleaching. When it reaches a value of 8, the likelihood of coral bleaching and extensive mortality increases. By August, as per the visual representation, heat stress in much of the affected region had already far exceeded both thresholds. NOAA reported that by late September 2023, the cumulative heat stress reached 22°C-weeks (40°F-weeks), nearly tripling the past record for the area.

Early Indications and Consequences of Coral Bleaching

Signs of bleaching were discernible in specific regions as early as July. Notably, coral reef areas close to the Florida Keys, Cuba, and the Bahamas were among the first to display elevated cumulative heat stress levels. Although Hurricane Idalia in late August led to a temporary cooling of surface waters, the relief was short-lived.

By the middle of October, the waters surrounding the Florida Keys had been designated a bleaching watch area. Meanwhile, marine environments around certain parts of Cuba and the Bahamas were placed under bleaching alert level 2, the most critical level on the scale, indicating that severe bleaching and a high probability of mortality were expected.

Data for this report was sourced from NASA Earth Observatory animations created by Wanmei Liang, using Daily 5km Degree Heating Weeks data from Coral Reef Watch. Additional coral reef data was obtained from UNEP-WCMC, WorldFish Centre, WRI, TNC.

Frequently Asked Questions (FAQs) about Coral bleaching 2023

More about Coral bleaching 2023

• NOAA’s Coral Reef Watch
• NASA Earth Observatory
• UNEP-WCMC
• WorldFish Centre
• World Resources Institute (WRI)
• The Nature Conservancy (TNC)
• El Niño and Climate Change
• Coral Bleaching and Climate Change
• Marine Ecosystems and Climate Change
• Sea Surface Temperature Records