The Lobster Came Back, It Couldn't Stay Away

January 2, 2003
Mary Vallis, National Post, with files from news services

Spiny lobsters have an uncanny ability to find their way home, even after being blindfolded, driven in circles and plunked in unfamiliar waters, researchers have found.

Just like a homing pigeon, a Caribbean spiny lobster (Panulirus argus) can determine where it is situated in relation to its home den, which is most often a narrow crevice in a coral reef. They seem to have an internal global positioning system that can figure out their location.

"No matter what we did, the lobsters figured out the direction that they needed to walk in order to go back home," said Dr. Kenneth Lohmann, an associate professor of biology at the University of North Carolina at Chapel Hill.

The results are astonishing, Dr. Lohmann said, because they mark the first time an invertebrate has demonstrated such precise navigation.

"It's really a rather remarkable finding if you think about it -- these little crustaceans being able to somehow determine their position under conditions in which humans would be completely lost."

To test the lobsters' skills, Dr. Lohmann and Larry Boles, a doctoral student, captured dozens off the Florida Keys and stowed them in dark, covered tanks. They then relocated the lobsters by boat, taking circuitous routes up to 30 kilometres long to confuse them.

The next morning, the crustaceans were blindfolded -- the researchers placed rubber caps over their eye-stalks -- and then released them while tethered to a tracking system that monitored their movements. They always scuttled toward home.

The researchers suspected the lobsters navigated by an internal magnetic compass and tested the idea with a second set of tests. This time, they captured lobsters and moved them 37 kilometres away by truck. The lobster tank was suspended by ropes so it would swing erratically. On half of the trips, the tank was surrounded by swinging magnets that were strong enough to affect compasses placed nearby.

The lobsters were blindfolded the next morning. Both groups gravitated toward the place where they had been captured.

"Our results demonstrate for the first time that an invertebrate animal is capable of true navigation," the researchers write in today's issue of the British journal Nature.

"The results provide the most direct evidence yet that animals possess and use magnetic maps. Similar mechanisms might function not only in lobsters, but in various animals that migrate or home, including certain fishes, amphibians, reptiles and birds."

The spiny lobster -- which lacks the predominant claws for which lobsters are best known -- probably developed its navigational expertise because of its lifestyle, Dr. Lohmann said. The crustaceans scuttle out of their dens at night, roam the coral reef for food, then return to their individual dens.

Scientists have been debating for nearly a century how birds, bees, frogs and other small creatures are able to find their way to specific feeding grounds or reproduction sites. The latest theory is based on the discovery of a naturally iron-rich substance in the brain, called biogenic magnetite, that responds to magnetic waves.

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