Cy­clones ‘help’ reef

Port Douglas & Mossman Gazette - - NEWS - AN­GELIQUE PAT­TER­SON

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.”

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