The Great Barrier Reef is experiencing a sixth mass bleaching event

The Great Barrier Reef is experiencing a sixth mass bleaching event, the marine park’s authority confirmed today after completing aerial surveys of the region. This is the fourth time the region has bleached in the past six years, raising concerns that the world’s largest reef system will be unable to recover.

Corals are marine invertebrates or animals not possessing a spine. Each coral is called a polyp and thousands of such polyps live together to form a colony, which grows when polyps multiply to make copies of themselves.

Corals share a symbiotic relationship with single-celled algae called zooxanthellae.

The algae provide the coral with food and nutrients, which they make through photosynthesis, using the sun’s light. In turn, the corals give the algae a home and key nutrients. The zooxanthellae also give corals their bright colour.

Australia’s Great Barrier Reef is the world’s largest reef system stretching across 2,300 km. It hosts 400 different types of coral, gives shelter to 1,500 species of fish and 4,000 types of mollusc.

Coral Bleaching happens when corals experience stress in their environment due to changes in temperature, pollution, or high levels of ocean acidity.

Under stressed conditions, the zooxanthellae or food-producing algae living inside coral polyps start producing reactive oxygen species, which are not beneficial to the corals.

So, the corals expel the color-giving zooxanthellae from their polyps, which exposes their pale white exoskeleton, giving the corals a bleached appearance. This also ends the symbiotic relationship that helps the corals to survive and grow.