The Great Barrier Reef has experienced a third mass coral bleaching event in five years, the most widespread bleaching event on record, with the south of the reef bleaching extensively for the first time
Coral reefs are some of the most vibrant marine ecosystems on the planet — between a quarter and one-third of all marine species rely on them at some point in their life cycle.
- Coral polyps are tiny, soft-bodied organisms related to sea anemones and jellyfish.
- Coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate.
- Reefs are important because they protect shorelines and coastal regions from erosion and extreme weather events.
- They are also source of food security for millions of people around the world.
- According to a study by the United Nations on the Economics of Ecosystems and Biodiversity, coral reefs benefit about 850 million people worldwide, with at least 275 million depending directly on reefs for livelihoods and sustenance.
The Great Barrier Reef.
Covering nearly 133,000 square miles, it is the world’s largest coral reef and is home to more than 1,500 species of fish, 411 species of hard corals and dozens of other species.
It’s a vital resource to Australia’s economy, contributing more than $5.6 billion annually and supporting tens of thousands of jobs.
Coral bleaching happens when corals lose their vibrant colors and turn white.
- Coral are bright and colorful because of microscopic algae called zooxanthellae.
- The zooxanthellae live within the coral in a mutually beneficial relationship, each helping the other survive.
- But when the ocean environment changes— When water is too warm, corals will expel the algae (zooxanthellae) living in their tissues causing the coral to turn completely white.
- As the algae leaves, the coral fades until it looks like it’s been bleached.
- Bleaching doesn’t kill coral immediately. But if temperatures remain high, eventually the coral will die, destroying a natural habitat for many species of marine life.
- As bleaching expands and becomes more frequent, corals are at greater risk of dying off — and that will be devastating not only for the region’s biodiversity, but for the thousands of people whose life and livelihood depend on the reefs.
- The UN’s Intergovernmental Panel on Climate Change found the published evidence suggested a majority of tropical coral reefs would disappear even if heating was limited to 1.5C and would be “at very high risk” at 1.2C.
- Four severe bleaching events have occurred in 2002, 2016, 2017, and now in 2020.
- It takes about a decade for the fastest growing corals to make a full recovery. As bleaching events become more frequent, there are fewer opportunities for the corals to rebound. That could have a huge impact on whether the reefs can recover.
Factors causing Coral bleaching
- High water temperature and bright sunlight are the primary triggers of mass bleaching,
- Calm and clear conditions with minimal current can exacerbate the stress and intensify bleaching such as extreme low tide and exposure
- Lack of wind and currents may result in less mixing of water layers, clearer seas, and deeper penetration of solar irradiance (i.e., the amount of light that penetrates the water column).
- Reefs dominated by resistant coral types may bleach less severely, or bleach later, than reefs dominated by susceptible species.
- Oxygen starvation caused by an increase in zooplankton levels as a result of overfishing
- Increased sedimentation caused due to silt runoff from human activities on riverbed
- Changes in Ocean salinity and Ocean acidification due to elevated levels of CO2 caused by air pollution
- Elevated sea levels due to global warming
- Pollutants such as oxybenzone, butylparaben, which are common sunscreen ingredients that are non-biodegradable and can wash off of skin and mix with water.
- Being exposed to Oil or other chemical spills