( se what the home reef smelt like when ...)Baby fish 'smell their way home'

The team exposed tiny fish larvae in a tank to pure streams of water from four different reefs. To their amazement, within minutes a surprisingly high percentage of baby fish had congregated in the water flow from their home reef.

"It was a lot more than you'd expect to happen by pure chance ?and it applied, in differing degrees, across several species of fish," Mike says.

The fish could also be responding to other stimuli, including distant noise off a reef and the behaviour of other fish, but the team concluded that smell was probably the dominant factor leading the babies home.

"Every reef gives off its own unique chemical signature, a rich mixture of the proteins and amino acids emitted by corals, all the plankton and mucus from its life. We think baby fish can pick this up and distinguish it from other reefs.

"We think some fishes then choose currents that smell like 'home' and swim up them. The ones that cannot do this perish. The ones that get home preserve the unique 'ethnic' make-up of their tribe ?and so continue the process of evolving into separate new species."

How the fish learn the unique smell of home is a mystery still. The researchers theorise that it is imprinted on them either when they are an egg inside their mothers, a fertilised egg swept around on the bottom, or new-hatched fry loose in the stream or brooded in their parents' mouths.

"An egg, even a fry, hasn't a fully developed sense of smell, but it may have a way of absorbing the local molecules and then recognizing their signature as "home" when it grows up a bit and is ready to settle," Mike says.

"This evidence that individual coral reefs play such a key role in the emergence of new species is a fresh reason to take even greater care in how we look after them."