Australian scientists have discovered the molecular mechanism that leads to mass death of corals worldwide as the Earth’s climate changes. Coral bleaching is one of the most devastating events affecting coral reefs around the planet, which is triggered by rising water temperatures.
It occurs when the corals and their symbiotic algae become heat-stressed, and the algae, which feed the corals, either die or are expelled by the coral.
Now, scientists from the ARC Centre of Excellence for Coral Reef Studies and James Cook University have revealed that a complex cascade of molecular signals leading up to the self-inflicted death of corals and their symbiotic algae is triggered as sea water begins to warm.
Working with Acropora corals from the reef at Heron Island, the researchers found the cascade begins at ocean temperatures as much as 3 degrees lower than those normally associated with coral bleaching.
And the process culminates in ‘apoptosis’ or programmed cell-death – a situation in which living organisms (including corals and humans) deliberately destroy their weakened or infected body cells, effectively a form of ‘cell suicide’ or amputation designed to protect the organism as a whole.
"Our results suggest that the control of apoptosis is highly complex in the coral-algae symbiosis and that apoptotic cell death cascades potentially play key roles in tipping the cellular life or death balance during environmental stress prior to the onset of coral bleaching,” explained lead author Dr Tracy Ainsworth.
“It is also clear that this chain reaction responds significantly to subtle, daily changes in the environment and to sea temperatures which were generally thought till now to have little impact on the function of coral and its symbiotic algae,” she said.
Paradoxically, the team’s research identified molecular signals both promoting and discouraging programmed cell-death in the corals.
The findings have been published in the latest issue of Scientific Reports published by Nature.