8 June 2007

Freshwater crabs thrive in Roman ruins

Agençe France-Presse
Throughout the rise and fall of Rome's emperors, monarchs and politicians an inconspicuous crab has reigned supreme in the ruins.
Freshwater crabs thrive in Roman ruins

A colony of the freshwater crab Potamon fluviatile is still living in underground canals first built by the Etruscans nearly 3,000 years ago. Credit: Wikipedia

ROME: Throughout the rise and fall of Rome’s emperors, monarchs and politicians an inconspicuous crab has reigned supreme in the ruins.

Potamon fluviatile, an unassuming freshwater crab, has shown superior staying power, thriving in the canals built by the Etruscans nearly 3,000 years ago, Italian zoologists say.

The ancient ruins of Trajan’s Forum in the heart of the Eternal City has provided the ideal habitat for the crustacean, which is much larger than its counterparts in lakes and rivers, said Massimiliano Scalici of the University of Rome III.

Greek import

The narrow canals that flow under Trajan’s Forum lead to the Cloaca Massima, the ancient Roman sewage system built in the sixth century BC initially to drain local marshes.

“Early results of a genetic analysis that we are doing show that the genes of the crabs at Trajan are very close to those of Greek freshwater crabs,” Scalici said. “So it’s very likely that they were introduced by the Greeks 2,500 or 3,000 years ago, which means they were here even before Rome was founded in 753 BC.”

While in more natural settings the crab grows to a length of five centimetres, it is more robust in the ruins, growing to more than eight centimetres. “Once we found a moult (shed exoskeleton) measuring 12 centimetres!” Scalici exclaimed during a tour of the site.

“Gigantism is one animal response to isolation, and it is a phenomenon that requires a long time,” he noted.

Low profile

The hardy crabs have also “shown extraordinary adaptation” in a habitat that “is obviously very different” from that inhabited by their cousins in nature, Scalici said.

Rome’s crabs have a longer life expectancy at 15 years instead of 10 to 12 years, he noted.

But for all its success, Potamon fluviatile has kept a low profile in Rome, revealing its existence only a decade ago.

It was in 1997 that Scalici and another zoology student happened on a specimen minding its own business under a stone in Trajan’s amphitheatre, part of the largest of Rome’s imperial forums, built in 113 at the territorial height of the Roman Empire.

Intrigued, a small group of researchers from the University of Rome III went to work studying the only known colony of freshwater crabs living amid the noise, pollution and humans of a large city.

“We think there are about 1,000 of them, but it’s hard to say because we can’t mark their shells, given that they shed regularly,” Scalici said.

The researchers are considering fitting specimens with microchips under their shells, but they are expensive, he added.

Not too tasty

Scalici said the crabs have very few predators, since stray cats – a frequent sight at Roman ruins – “aren’t interested, and gulls don’t come at night because the site is lit up all the time.”

As for their diet, the omnivorous crustaceans feed on algae, insect larvae and snails, as well as the occasional cigarette butt and fast-food container.

The amphibious creatures burrow deep to their hideaways, sometimes reaching several metres below the ruins, leaving small mounds of dirt on the surface.

“Of course we are still working with hypotheses – the genetic study isn’t finished – but it’s very tempting to believe that (the crabs were introduced by the ancient Greeks), especially because lots of aspects like the gigantism suggest that the crabs have been here for a really long time,” Scalici said.

As the crustaceans have managed to survive the urban environment so long, Scalici hopes their age-old tranquillity will not be disturbed by work on a new subway line, which is to pass close to the Forum’s foundations.

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