Return of a castaway: the gripping story of a boring clam - shipworm

Science News, August 3, 2002 by Kristin Cobb

There maybe special value to T. turnerae itself because it both cleaves cellulose and fixes nitrogen, Waterbury says. Cows' diet of cellulose has to be supplemented with nitrogen, he explains. In the 1980s, the Department of Agriculture experimented with using T. turnerae to convert cellulose into nitrogen-rich cattle food, but efforts were stopped because of difficulties of working in saltwater. Waterbury thinks the application may still be viable, however.

Scientists are also studying the bacteria-shipworm liaison as a model for symbiotic and pathogenic animal-microbe interactions. For example, several scientists have been investigating how T. turnerae man ages to infect shipworms. Do the shipworms pick up bacteria from the environment or pass them down from generation to generation in their eggs? Some data support each scenario. The answer may help scientists understand how other infections spread.

Bacterial symbionts enabled shipworms to evolve into animals that live in and eat wood--transforming them into economic and historic giants. "Otherwise," Waterbury concludes, "they were just lousy clams."

RELATED ARTICLE: Shadow of history.

Sailors have battled shipworms since ancient times.

In the first known historical reference to shipworms, a Greek philosopher in 350 B.C. described them as a terrible plague for which there was little remedy. Historians say that both the Greeks and the Romans covered their wooden boats with lead, pitch, and tar to protect against shipworms. Even earlier, more than 3,000 years ago, the Phoenicians and Egyptians slathered their wooden boats in pitch and wax--probably to protect against shipworms, barnacles, and myriad other organisms that malign wood.

Shipworm devastation was rampant through the European age of exploration. During Columbus' fourth voyage, which began in 1502, he was forced to stop in the Caribbean because his ships were too damaged by shipworms to continue. Shipworm appetites also helped Britain sink the Spanish Armada in 1588.

Shipworms hitchhiked all over the world on explorers' ships. For 500 years, wooden ships opening the way to newfound seas were "Johnny Shipwormseeds" spreading wood-boring clams instead of apple trees, says James T. Carlton of Williams College in Williamstown, Mass.

Sixteenth- and 17th-century sailors tried just about everything to guard against shipworms. They coated their ships with a veritable stew of noxious and obstructing materials: heavy black tar, pitch, calfskin, cows' hair, ashes, glue, moss, and charcoal. They also brought their boats to fresh or freezing water for a cure. Salt-loving shipworms can seal themselves off from the deadly freshwater for only a few weeks. Freezing them brings a swifter death. Sailors would also burn the outer surface of their boats--a method that on occasion led to more damage than it prevented.

In the late 18th century, at great expense, the British Navy covered the bottoms of all its warships with copper plating, the most effective deterrent against shipworms at that time. Besides forming a barrier, copper leaks ions that are toxic to animals, including shipworm larvae. In the 19th century, copper alloys and paints replaced copper plating.