Cyclones ‘help’ reef
CYCLONES might not be man’s best friend but for struggling coral in the Great Barrier Reef they may be just what the doctor ordered.
Dr Marji Puontinen, an honorary fellow at University of Wollongong, has been working alongside PhD student Adam Carrigan to model the impact of tropical cyclones on coral reefs of the GBR.
Coral bleaching is on the increase and occurs when algae living inside coral leaves because the water is too warm.
“They’re really sensitive to water temperature so water needs to be warm enough to survive but even one degree celsius above what they prefer and they will come under stress and if it lasts long enough they can bleach,” Dr Puontinen said.
“They have micro-organisms which are symbiotic, little tiny algae that live inside its pores and that’s how coral gets its colour.
“When the microscopic beastie gets upset when the water is too warm, it jumps ship and the coral turns to white.”
Dr Puontinen’s study showed that depending on duration, intensity and strength of a cyclone, it can create an up-well affect in the ocean and bring the colder water at the bottom of the ocean to the surface.
“The cyclone-induced cooling, to have an effect on the reef, needs to happen at a time when the sea surface temperature is hot and putting reefs under thermal stress,” she said.
“If the thermal stress doesn’t last too long the algae can come back in or a different one comes back in once stress is relieved.”
When Cyclone Yasi hit the reef, it caused a large area of cooling, especially considering it arrived just after Cyclone Anthony.
“Cyclone Anthony had a really slow transit time through the Coral Sea and helped cooling happen because there was plenty of time for the wind and wave action to bring up cool water,” Dr Puotinen said.
“Definitely in 2011 after Yasi there was a persistent signal of cooler temperatures across quite a large area of the Great Barrier Reef.
“It’s still premature, but we are looking at things like how often cyclone cooling happens at times when and places where corals are under thermal stress.
“There is a chance some reefs in particular regions might be helped by cyclones to get through the future world where water is going to be a lot warmer.”