Nemo's finding his nose troubled by climate change

The tiny reef clownfish made famous in the animated movie Finding Nemo is the latest victim of climate change, according to a paper released today.

In the latest Proceedings of the National Academy of Sciences journal, marine researcher Dr Philip Munday shows that ocean acidification caused by rising CO2 emissions affects the orange clownfish larvae's sense of smell, which is crucial to it finding a suitable and safe home.

Munday, of the Australian Research Council Centre of Excellence for Coral Reef Studies says clownfish larvae use their sense of smell to guide them to reefs and to distinguish between good and unsuitable homes. "Disruption to this process would have significant consequences for the replenishment of adult populations and could lead to the decline of many coastal species," lead author Munday says.

For the study, the clownfish (Amphiprion percula) were reared in water at the same pH level as current levels in the open ocean and in water at pH levels consistent with 1000 parts per million CO2. Currently, CO2 levels in the ocean are now about 390 parts per million. The Intergovernmental Panel on Climate Change predicts that this may rise to as high as 1000 parts per million by 2100. The fish were then placed in specially designed tanks that contained streams of water in which the leaves of the tropical rainforest tree Xanthostemon chrysanthus or swamp tree Melaleuca nervosa had been added. In water at pH levels on par with today's ocean, the clownfish spent 93% of their time in the stream of water in which the rainforest leaves had been soaked. The fish completely avoided the Melaluca stream of water.

However under the 2100 scenario, the clownfish spent more than 80% of their time in the Melaluca stream. The ability to discriminate between water containing the scent of their parents and other adult clownfish was also lost in the more acidic water. He says this is an important quality as it helps stop inbreeding between juvenile clownfish and their parents.

This latest paper builds on a 2008 study that showed larval clownfish can discriminate the smell of water from their birth reef compared with water from other reefs, and that they use olfactory cues to identify suitable settlement sites. Munday says he suspects the clownfish findings will translate to other reef fish species. He says it is unlikely the marine animals will be able to adapt to the rapid increase in ocean acidity.

The human-induced change is causing pH to decline at a rate more than 100 times faster than at any time in the past 650,000 years, Munday says. "It is unlikely that genetic adaption by most marine organisms, perhaps except those with very rapid generation times, will be able to adapt to keep pace with such a rapid rate of change."