Marine heatwaves brought about by climate change are known to be responsible for mass mortality on some of the planet’s most iconic coral reef systems.

However, scientists have discovered that an extreme weather event that resulted in rapid sea temperature drops of up to 10 degrees was the primary cause of a catastrophic coral die-off event.

Combined with widespread rise in harmful algal blooms, the extent of collapse of the reefs in Costa Rica’s section of the Eastern Tropical Pacific in 2009 was abnormally high.

The two factors resulted in coral cover at some sites decreasing by between 20% and 100%, with the levels of recovery also varying significantly in the years since.

In a new study, published in the journal PeerJ, researchers say their findings demonstrate the effects of upwellings – which result in sea temperatures suddenly plummeting – are a key factor that need to be consider when trying to manage reef systems.

The research was conducted by an international team of scientists led by the University of Plymouth, working alongside partners including Raising Coral and ACG, who promote coral reef conservation in Costa Rica.