In a devastating ecological event, almost two out of three corals across popular tourism areas of the World Heritage-listed Ningaloo reef have perished following an unprecedented marine heatwave along the Western Australian coastline.
A Silent Underwater Graveyard
Coral scientist Zoe Richards, an associate professor at Curtin University, described confronting scenes during her surveys. She examined 1,600 individual corals across eight sites spanning 40 kilometres as the bleaching event peaked in March.
"The bleaching was so confronting because it was so expansive," Richards said. When she returned with researcher David Juszkiewicz at the end of October, the situation had dramatically worsened. Approximately 1,000 of the 1,600 originally recorded corals had died.
"You go in hoping the corals you saw that were partially bleached might have recovered. Unfortunately the scale tipped to mortality," Richards explained. "Most of the data is showing that any coral that bleached in March went on to die."
Ecological Collapse in Northern Lagoon
The affected areas between the Osprey and Tantabiddi sanctuary zones have undergone what scientists term a "profound ecological simplification". The northern parts of Ningaloo's lagoon, popular with tourists for their accessible coral gardens, have suffered a marked loss of biodiversity and reduction in habitat complexity.
Richards described the eerie silence during her dives. "They're incredible places where you can swim right off the beach and see all this luxurious coral," she said. "Diving and snorkelling on these reefs is usually accompanied with 'lots of popping and cracking' sounds of fish and other animals. It was deathly silent."
The marine heatwave swept across Western Australia last summer and autumn, turning corals white from heat stress from Ningaloo to Ashmore reef 1,500 km to the north-east. When corals remain in unusually warm water for extended periods, they expel the algae that provide colour and nutrients, leaving behind translucent flesh revealing the white skeleton.
Global Climate Crisis Reaches Tipping Point
This catastrophic event forms part of the fourth and worst global mass bleaching event on record, which has exposed more than 80% of reefs in over 80 countries to temperatures high enough to cause bleaching.
"Corals act like thermometers for the ocean," said Richards. "When they bleach, they are sending out a clear signal that the temperature is too high. They don't talk, but they are signalling to us very clearly. We're on the brink of catastrophic ecosystem decline. This is happening everywhere."
The heating is primarily caused by greenhouse gases released from burning fossil fuels and deforestation, with about 90% of the extra heat on our planet being absorbed by the ocean.
Richards, who conducted the research in partnership with the Minderoo Exmouth Research Laboratory, expressed profound concern for the future. "I have devoted my whole life to coral research. I am starting to visualise the point where all we have left of corals and reefs is memories."
