Widesperad Coral Bleaching (II)

Effects of Coral Bleaching

Coral bleaching has devastating effects on coral reef ecosystems. When corals bleach, they expel the symbiotic algae that provide them with nutrition. This leads to starvation and death of the corals if bleaching persists. Widespread coral mortality can destroy entire reef ecosystems. Coral reefs support incredibly diverse marine life, so the loss of corals means the loss of habitat for many species. Mass bleaching events have caused up to 90% mortality on some reefs, leading to a dramatic decrease in fish populations and biodiversity. The destruction of coral reefs also heavily impacts human communities. Many people depend on reefs for tourism, fishing, and coastal protection from storms. Loss of coral reefs means loss of income and food sources for these communities. Fishing and tourism industries suffer greatly when reefs die off.

Major Coral Bleaching Events

Coral reefs around the world have experienced severe bleaching events over the past few decades as ocean temperatures have risen. Some of the major events include:

1998 Coral Bleaching Event

In 1998, an estimated 16% of the world's reefs were badly damaged or destroyed by bleaching triggered by unusually warm ocean temperatures. This event was associated with a strong El Niño weather pattern and was the first global-scale bleaching event recorded. The Great Barrier Reef off Australia experienced major bleaching, with over 60% of reefs affected. Other regions like the Maldives, Seychelles, Sri Lanka and islands in the Caribbean also saw extensive bleaching.

2010 Coral Bleaching Event

Another major bleaching event took place in 2010, again driven by El Niño conditions. Coral reefs across the Indian Ocean, Southeast Asia, the Caribbean, and parts of the Pacific were impacted. Up to 80% of coral was bleached in the Andaman Sea, and over 40% of reefs surveyed on the Great Barrier Reef showed signs of bleaching.

2014-2017 Global Coral Bleaching Event

The longest and most widespread coral bleaching event on record occurred from 2014-2017. It affected reefs across the Pacific, Indian Ocean, Atlantic, and Caribbean. Over 70% of the world's reefs experienced bleaching, with the Great Barrier Reef being severely impacted - up to 50% of its shallow-water corals died in the northern region. Back-to-back bleaching also occurred over multiple years, further damaging reefs already under stress. This event highlighted the vulnerability of coral reefs to warming oceans.

Widespread Coral Bleaching (I)

 What is Coral Bleaching?

Coral bleaching is a phenomenon that occurs when coral polyps expel algae called zooxanthellae from their tissues. This gives the coral a stark white appearance, resembling bleached or dead coral. Coral bleaching is caused by abnormally warm ocean temperatures, usually during prolonged periods of warmer weather. When water temperatures rise just 1-2°C above the normal local seasonal maximum, corals become stressed. They react by ejecting the symbiotic algae living inside their tissues. These algae normally provide up to 90% of the coral's energy through photosynthesis. Without them, the coral loses its major energy source and turns translucent and white, revealing the stark white calcium carbonate skeleton beneath. This bleached appearance signals that the coral is severely stressed and at risk of death.

Causes of Coral Bleaching

Coral bleaching is primarily caused by increased ocean temperatures. When water temperatures rise, corals become stressed and expel the symbiotic algae that gives them their color, causing them to turn white. This bleaching makes it harder for corals to survive. Several factors contribute to increased ocean temperatures and coral bleaching:

Increased Ocean Temperatures - Warming oceans are the main driver of mass coral bleaching events. Even an increase of just 1-2°C can cause bleaching.

El Niño Weather Patterns - El Niño brings warmer water temperatures to tropical and cold-water regions, causing bleaching. The strong 2015-2016 El Niño triggered severe bleaching at reefs around the world.

Climate Change and Global Warming - Climate change is increasing average ocean temperatures, making bleaching events more frequent and severe. Since the 1980s, mass bleaching events have occurred during most El Niño years.

Pollution - Pollution from agricultural runoff and coastal development can further stress corals, increasing their vulnerability to bleaching.

Overfishing - Overfishing key herbivorous fish can allow algae to overgrow and outcompete corals. This added pressure makes it harder for corals to recover from bleaching.

Rising ocean temperatures due to human-caused climate change are the primary driver of increased coral bleaching worldwide. El Niño and local stressors like pollution magnify the impacts of warming seas. Reducing carbon emissions and local threats are key to coral reef conservation.