Coral Reef Bleaching: Red flags on our oceans' health

It’s a common misconception that coral is a plant growing in the sea, when in fact it's an animal, specifically a marine invertebrate within the class Anthozoa of the phylum Cnidaria. They normally live in colonies formed of many identical individual polyps.

Despite the fact that some corals can catch their food through stinging cells, most of them depend on microscopic marine algae called zooxanthellae, which are located in their tissues and give the corals their vibrant and beautiful colors. Zooxanthella provides the coral with nutrition and energy from the sun through photosynthesis, which allows them to grow and reproduce.

But the hasty change in climate caused the water temperature to rise. When corals are exposed to such conditions, even a slight change of 2 degrees Fahrenheit, they get stressed, which causes them to expel the zooxanthellae that live within their tissues and give them their color, leaving their white skeleton exposed, a phenomenon called coral bleaching.

Undergoing a bleaching event doesn’t necessarily mean the coral is dead, but if the water temperature stays high, the algae won’t return to the coral, and eventually, the reef will starve to death. Even with the right conditions, the coral reef may take years to recover. There are also other factors that can cause this stress, such as pollution and low tide.

The climate change and rising temperature of the oceans caused by emissions of greenhouse gases have led to five mass bleaching events along the reef in 1998, 2002, 2016, 2017, and 2020. According to Prof. Terry Hughes, a leading expert on coral bleaching at James Cook University, the sixth event is on its way.

The report The Status of Coral Reefs of the World: 2020 by the Global Coral Reef Monitoring Network (GCRMN) indicates a loss of 14% of coral reefs around the world due to bleaching events between 2009 and 2018.

The first mass event was recorded on the Great Barrier Reef in the summer of 1997–1998. Scientists from GBRMPA (the Great Barrier Reef Marine Park Authority) found that 74% of inshore and 21% of offshore reefs suffered from a bleaching event. Less than 5% of inshore reefs suffered high mortality as most reefs recovered, but 70% of coral was lost in the Palm Island area. Another bleaching event was recorded in Western Australia in 1998, when a heat wave caused mass bleaching in the Scott Reefs, which reduced coral cover by 80%.

In 2002 Across the 641 reefs observed, 54% of the reefs suffered from a bleaching event that was a little more severe than the previous one; the reef recovered with just a 5% recorded loss.

In 2016, high mortality in coral reefs was recorded in the Far Northern Management Area, between Port Douglas and Cape York, due to high ocean temperatures. Less severe bleaching was recorded in the southern parts of the Reef.

Abnormally warm sea surface temperatures earlier in 2017, along with the previous bleaching event, affected 2/3 of the Great Barrier Reef. and in 2020, a percentage of 60% of the 1036 reefs monitored in the Great Barrier Reef suffered bleaching at moderate and severe levels.

The decline of coral reefs can have catastrophic consequences for marine ecosystems, which are known to be the tropical rainforest of the sea. They form a habitat for thousands of species that depend on them for food, breeding, and protection from predators. A lot of these species form the base of the marine food chain; if they disappear, the entire chain will collapse and many creatures will go extinct.

Coral reefs are also important for human lives; they form a natural barrier from waves and provide safety for coastal communities. Linwood Pendleton, the study’s lead author and an international chair at the European Institute of Marine Studies, said, "The waves just came into shore full force. That can cause the loss of life. It can cause loss of property",  where he estimated that nearly 62 million people live less than 33 feet above sea level and less than two miles from a coral reef.

Corals are important for food safety in a lot of those communities; they provide an abundance of fish, and the absence of some links in the marine food chain will drive some creatures away as they will be deprived of the ground for food, spawning grounds, and shelter.

Coastal tourism has a major contribution to the economy, with the value of coral reefs estimated to be $37.8 billion per year; therefore, the decline of reefs' health will have a bad impact on these economies.

Normally, coral can return to its healthy state provided that the temperature drops to standard degrees. As long as it stays high, coral will stay in a vulnerable state and be more subjected to mortality and the inability to feed, grow, and reproduce.

We are killing our planet, and the issue of climate change and its drastic consequences on all life forms must be addressed, starting with a clear understanding of the dire situation we are facing followed by immediate actions to reduce emissions and greenhouse effects that are warming our climate. We can reduce our carbon footprint by driving less, using bikes and public transportation, using less energy at home, recycling, which helps reduce the amount of waste that goes to landfills, supporting sustainable businesses that recycle and use renewable energy, and planting trees whenever and wherever possible.