WELLINGTON, May 7 (Xinhua) -- Global warming might be killing off many species of coral as the world's oceans acidify, but the future for biodiversity in coral reefs might not be as bleak as previously forecast, according to a study by New Zealand and Australian scientists.

"It has been predicted that many reefs will end up being dominated by algae rather than corals, which will have negative effects on biodiversity and ultimately on the ability of humans to derive protein from reefs," marine biologist Dr James Bell, of New Zealand's Victoria University, said Tuesday.

"However, we propose an alternative scenario -- as sponges and corals respond differently to changing ocean chemistry and environmental conditions, we may actually see some coral reefs transforming into sponge reefs," Bell said in a statement.

Bell and scientists from Victoria University, the University of Auckland and the Australian Institute of Marine Science found paleontological evidence from more than 200 million years ago that suggested past ocean acidification events were followed by a mass extinction of coral species and subsequent proliferation of sponges.

The scientists also observed several sites, including places in the Caribbean, Atlantic and Indo-Pacific, where sponges had already increased in abundance as corals declined.

Despite the important function sponges played on coral reefs, including filtering nutrients and providing a habitat for other species, most research to date had focused on the future of corals.

"Coral reefs provide a home for around one quarter of the world 's marine species, so understanding their future is incredibly important," he said.

Further research on the impacts of ocean acidification and ocean warming on coral reef sponges was urgently required to better protect reefs and understand how they could function in the future.