Climate change endangers Nemo

Nemo the clownfish will lose the ability to smell the way home, as climate change makes the world’s oceans more acidic, new research says.

A team of scientists from Australia, Russia and Norway have discovered that as seawater becomes more acidic, baby clownfish the stars of the Disney cartoon Finding Nemo lose the scent cues that guide them home from the open ocean to the coastal reefs where they were born.

”This is a disturbing finding, with potentially devastating consequences for marine life. It could lead to a decline in coastal reef species,” James Cook University marine biologist Philip Munday said.

The research results have demonstrated for the first time that ocean acidity is disrupting the natural behavioural decisions of marine life at critical stages in their life-cycles.

Dr Munday led a team that did laboratory tests on clownfish raised in normal and slightly acidic seawater to see if their sense of smell was affected.

”It was completely unexpected. We found the fish became confused when the water was more acidic than normal, and were attracted to smells they would normally avoid as indicating reef habitat was unsuitable.”

The tiny orange clownfish larvae, less than 1cm in length, are swept off their home reefs by wave action and into the open ocean when they are only a few days old.

The baby Nemos use their acute sense of smell to find their way back, and can detect a distinct whiff of difference between their preferred habitat of seawater surrounded by rainforest-fringed islands and unsuitable seawater from reefs without islands.

In normal seawater, clownfish are strongly attracted to scents from anemones on their home reefs and tropical rainforest trees on nearby land, but avoid the smell of swamp trees like melaleucas or tropical grasses.

Clownfish reared in slightly acidic seawater were attracted to a range of environmental smells, including those they normally avoided, but those reared in more acidic seawater showed no response to scent cues at all.

The research findings were published online this week in the Proceedings of the National Academy of Sciences USA.

Dr Munday said any disruption to the homing ability of clownfish could affect the survival of fish populations.

”It would potentially affect their ability to find the right habitat, and we don’t know if the loss of the scent cues is reversible. The loss of that homing ability would affect their ability to find the right place to live and to lay their eggs.”

In the paper, the research team says ocean acidification, caused by the absorption or rising carbon dioxide emissions at the ocean surface, is a serious threat to marine ecosystems.

”At least 30 per cent of the human-generated carbon dioxide released into the atmosphere in the past 200 years has been absorbed by the oceans,” the paper says.

This has caused the ocean to acidify at a rate about 100 times faster than at any time in the past 650,000 years.

Rosslyn Beeby, The Canberra Times, 5 February 2009. Article.

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