The Great Barrier Reef: How climate change is killing the world’s largest coral ecosystem

The Great Barrier Reef is the longest and largest reef complex in the world. it is located off the coast of Queensland, Australia, in the Coral Sea, and stretches for approximately 2,300 kilometers.

Australia’s Great Barrier Reef, the largest coral reef in the world, is facing an existential threat from rising ocean temperature, according to a study published by researchers from Melbourne University and other universities in Australia.

A Wake-Up Call | According to the research published in the journal Nature, water temperatures in and around Australia’s Great Barrier Reef have risen to their warmest in 400 years over the past decade, placing it under threat.

How Was The Study Conducted? | A group of scientists in Australia drilled cores into the coral and analysed the samples to measure summer ocean temperatures going back to 1618. The information was combined with ship and satellite data going back around a hundred years. The results show ocean temperatures that were stable for hundreds of years, began to rise from 1900 onwards as a result of human influence. An average annual warming of 0.12 degree Celsius per decade was observed from 1960 to 2024, for the January to March period.

What Is Coral Reef? | Coral reef is a living creature. Contrary to the popular belief, corals are not plants, they are animals – distant relative of jellyfish and anemones.

Great Barrier Reef | The Great Barrier Reef is the longest and largest reef complex in the world. it is located off the coast of Queensland, Australia, in the Coral Sea, and stretches for approximately 2,300 kilometers. It is made up of nearly 3,000 individual reefs and includes 400 types of coral, 1,500 species of fish, and 4,000 types of mollusc. It is the largest living structure on earth and the only one visible from space.

How Corals get their colour? | Corals have a symbiotic relationship with microscopic algae called zooxanthellae that live in their tissues. The calcium carbonate secretions from corals form hard and protective scaffolding where many colourful species of this single-celled algae reside. Like plants, these algae produce food through photosynthesis and are the coral’s primary source of energy. This arrangement between the corals and algae is beneficial for both. It provides algae with shelter and gives coral reefs their colour, and supplies both organisms with nutrients. The symbiotic relationship between algae and corals began more than 210 million years ago – that’s when the first dinosaurs appeared and earth’s continents were a single landmass known as Pangea.

Coral Bleaching | Heat stress causes coral bleaching, turning the colourful corals to a ghostly white, putting them at greater risk of death. Stressed coral expels the symbiotic algae from their tissues, causing them to turn white. The Great Barrier Reef has experienced five summers of mass coral bleaching in the last nine years – in 2016, 2017, 2020, 2022, and most recently in early 2024.

How Climate Change Affects Corals? | Change in ocean temperature is the leading cause of coral bleaching. Corals prefer temperatures between 23 and 29 degree Celsius. But, bleaching does not mean that corals are dead. Corals may not be able to reproduce or grow during a bleaching event, but they may be able to recover if the water cools down after a short period of time. Climate change has caused ocean temperatures to increase, and ocean heatwaves have become more frequent. As a consequence, bleached corals, may not get a chance to recover.

What Happens If Coral Reefs Die? | Coral reefs provide shelter to millions of species. No coral reefs mean these species lose their habitat and might perish. They also protect coasts from erosion, support tourism and livelihoods. The Great Barrier Reef contributes about $4.2 billion to Australia’s economy each year. It is estimated to support over 60,000 tourism jobs.