The brightly-coloured corals that make Australia's Great Barrier Reef one of the world's natural wonders will be largely dead by 2050 because of rising sea temperatures, according to a report released Saturday.

Instead of the rich environment depicted in the recent movie Finding Nemo, the coral reef will be bleached out and replaced by ordinary seaweed, costing the tourism industry billion of dollars, the report into the impact of global warming says.

Authors Hans and Ove Hoegh-Guldberg -- the head of Queensland University's marine studies centre and his economist father -- spent two years examining the effects of rising sea temperature on the reef for Queensland tourism authorities and the World Wildlife Fund for Nature (WWF).

Their 350-page report found no prospect of avoiding the "chilling long-term eventualities" of coral bleaching because greenhouse gases were already warming the seas as part of a process it said would take decades to stop.

"The argument for instant action is undeniable," WWF said in a statement. "Major reductions in greenhouse gas emissions must occur now, not in five or ten years time. This is likely to deliver major benefits to our societies both in the near-term and at times beyond 2050."