‘Nemo’ clownfish disorientated by loss of sense of smell

NEMO, the clownfish of Hollywood fame, might find a diminished sense of smell, not hearing, impedes him from finding his way home this year.

This loss of senses is being put down by scientists to acidification of the world’s oceans due to human carbon emissions.

Like many reef and coastal fish, clownfish are swept off their home reefs into the open ocean as babies and use acute senses of smell and hearing to find their way back.

Researchers tested clownfish raised in normal and slightly more acidic seawater to see what effect it had on their sense of smell.

They found the fish, normally acutely sensitive to different smells in the water, became confused when the water was more acidic than usual.

Lead author Philip Munday, of the ARC Centre of Excellence for Coral Reef Studies, said baby fish were strongly attracted to scents that they would normally avoid at the sort of ocean acidity levels that could occur by 2100.

They no longer responded to scent cues at all when acidity rose further.

“This is a disturbing finding because the tiny larvae of many coastal fish probably rely on scent cues in the water to help locate adult habitat,” Dr Munday said.

“Any disruption to their ability to navigate could have far-reaching implications for the future of these fish populations.”

Ocean acidification, caused by the absorption of human-released carbon dioxide at the ocean surface, is now recognised as a serious threat to marine ecosystems.

Every time we start a car or use electricity, a third or more of the CO emitted ends up in the ocean, turning its waters imperceptibly but inevitably more acidic.

At least 30 per cent of the human-generated CO released in the past 200 years has been absorbed by oceans, causing ocean pH to decline – that is to acidify – about 100 times faster than at any time in the past 650,000 years.

Brian Williams, Courier Mail, 4 February 2009. Article.

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