2001 WINNER

Life with tuna snapping at your tail

By Stephen Simpson

SOLO is having a hard day. His yolk sac has just run out and, if he doesn't eat soon, he will die. Just as he starts to sense a tasty microscopic shrimp within striking distance, a fearsome thunderbolt of a tuna hoots past, knocking him for six. Solo is a centimetre-long, week-old larval damselfish, and his odyssey has begun.

Despite all the care his parents could offer-the nest building, the long, sensuous courting dances, the daily egg preening-he now drifts with his thousands of siblings at the mercy of the ocean currents. Solo has about a one in 10,000 chance of survival in the big blue sea, where for four weeks, he must feed, grow, and master stalking his prey, all the time dodging predators. Only then will he be fit to return to a coral reef to begin his adult life.

This seemingly hopeless strategy has evolved in most coral reef fishes, both as a mechanism for dispersal-adults travel very little-and as a means of evading the treacherous ''wall of mouths'' formed by predators on the coral reef.

At 10 days old, Solo is getting stronger. Dave Bellwood's team at James Cook University on the Great Barrier Reef has found that larval fish can swim non-stop for eight days, covering istances up to 60 miles. This Olympian effort is equivalent to a human round-the-world swimming race. So, despite the ocean currents, it seems that Solo might have some chance of finding a coral reef, perhaps even the one on which he was born.

After Solo's ''ears''-otoliths- develop for another day, he senses the big blue is starting to talk. Otoliths are dense, prickly earbones that float in small hairy sacs in his head. Solo relies on them for his hearing and balance.

As he grows, so too must his otoliths. Now Solo is begining to detect an ancient rhythm, though the noise is very distant (coral reefs can be heard from 12 miles), and he starts to dance in its direction.

As the beat of the drum gets louder, Solo begins to pick out the different instruments. The sea herself is providing whooshes of breaking white horses and the occasional crash of a wave. But the animals on the reef are the real orchestra. Snapping shrimps form the reef's enormous percussion section (up to 300 shrimps may live on one sponge), their instruments imploding micro-bubbles at their claw-tips.

The soloists of the reef are nocturnal fish. Endowed with cunning mechanisms for producing and hearing sounds, these fish boom, squeak, rumble and hoot their way through the dark hours. This living nocturnal orchestra can raise the volume by 35 decibels, the difference between a quiet suburban street and the roar of rush-hour traffic.

Among the musicians of the reef, Solo's parents had timed their spawning activities carefully. They ensured that, when Solo finally arrives at a reef and its wall of mouths, it is during the new moon. This allows Solo to creep around under the cloak of darkness. And creep around he must, for this night is vital to his success. Using his now highly developed sense of smell, Solo instinctively sniffs out his favourite coral type and smells for older fish of his own species. He has made it.

And so Solo's odyssey concludes, the wanderer has returned to the reef, and adult life can now begin. Until recently, this odyssey was poorly understood-it was the ''black-box'' of fisheries management. But marine biologists are now learning to read Solo's inflight recorder.

His otoliths, which grow every day, can be read much like the rings on the trunk of a tree. By counting the rings we can now age larval fish, and from the distances between rings, study their growth rates. And that is not all. Dr Steve Swearer's team at the University of California has found that these rings contain a fingerprint of the chemical environment experienced during Solo's wanderings that can be deciphered using an ultra fine laser and a mass spectrometer. When compared to the chemistry of the surrounding waters, this enables us to see where Solo has been.

The more we can understand of the talents that Solo has developed on his journey, the more successful our management of fisheries and marine reserves will become. And the sooner the better, for Solo's odyssey was monumental enough without the recent success of a new and ruthless predator.

Man.